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Sample Answers of [Assignment: DNA & RNA]

Provided by Professor Dong, College of Life Sciences, Anhui University.

1) Compare the differences between DNA and RNA, structurally and functionally. Can you explain why DNA is more favorable as a genetic material?

Answer:

The differences between DNA and RNA in the structure

(1)   DNA contains deoxyribose in contrast to the ribose in RNA.

(2)    DNA has the thymine base, while RNA has the uridine instead of thymine. The thymine base-pairs with adenine only. The uridine can also pair with guanine in some cases, beside the normal U-A pairing.

(3)   DNA is commonly present as a double-stranded helix, while RNA is  single stranded with a few exceptions.

(4)   In the secondary structure, DNA follows the double-helix model. Cruciforms and hairpins are rare; for RNA, usually single-stranded, hairpins and pseudo-knots are common, leading to more complicated structures like the “cloverleaf” of tRNA.

 

The differences between DNA and RNA physiologically

(1)   RNA is more vulnerable for alkaline hydrolysis than DNA and more chemically active due to the extra –OH group at 2C

(2)   The UV absorbance feature is different: A260/A280=1.8 (DNA) 2.0(RNA)

The differences between DNA and RNA functionally

(1)   DNA acts as the genetic material, containing all inheritable information in most organisms

(2)   RNA has more diversified functions.

(a)   Normally, RNA is the intermediate for protein translation. mRNA works as the template; tRNA is the adaptor between mRNA and amino acids; rRNA is the essential parts of protein-synthesizing ribosomes

(b)   RNA can also be genetic material in some viruses

(c)    RNA can be a ribozyme catalyzing some special reactions, e.g. RNase P

(d)   Some small RNAs are important functional regulators, e.g. siRNA in RNA interfering.

Why DNA is more favorable as a genetic material

(1)   DNA is more resistant to hydrolysis than RNA. Furthermore, the double-helical structure confers much higher level of stability on DNA compared to RNA, which is critical for storage and vertical transfer of genetic information.

(2)   The semi-conservative replication of DNA and the high fidelity of DNA polymerases make it possible that the DNA is precisely copied from generation to next generation. While RNA cannot.

(3)   DNA has a sophisticate repair system which corrects damages and thereafter minimizes the loss or change of genetic information. While RNA has not.

 

2) Give your explanation about the semidiscontinuous mode of DNA replication? Can you describe the steps of replication for lagging strand?

(4)   Answer:

(5)   Replication of the lagging strand is discontinuous compared to the continuous replication of the leading strand. Therefore, multiple primers are synthesized for the lagging strand while a single primer is needed for the leading strand.

(6)   Reason: The DNA polymerase can work only from 5’à3’ orientation. To ensure the replication fork moves in one direction, different patterns of replication are applied to the two complementary strands.

(7)   Steps:

(8)   Initiation is the same for the both strands. When the replisome is assembled, the lagging strand is looped to make the both polymerase core-enzymes move in the same direction

(9)   A short Okazaki fragment is synthesized along the lagging strand. The sliding clamp releases and reloads onto the newly primed location to generate the next Okazaki fragment.(“trombone” model)

(10) RNA primers are removed and replaced with DNA by “nick translation” mechanism. The discontinuous patches are stitched together to form a continuous strand.

 

3) What is an insertion element? Describe the differences between the conservative and replicative transposons.

(11) Answer:

(12) IS: a simple transposon consisting only two inverted repeats surrounding the coding region of a transposase.

(13) Differences btw. the two transposition mechanisms:

(14) “cut-and-paste” vs. “copy-and-paste” patterns: conservative transposition leaves the original sequence broken while the replicative transposition make a copy either in the original and target sequence.

(15) For conservative transposition, transposase is sufficient along with the common polymerase and ligase. For replicative transposition, an extra resolvase is required to initiate a recombination process and catalyze the resolvation of the “cointegrate”.

 

4) Can you explain how to assure the fidelity of the DNA replication in bacteria?

(16) The basic fidelity of DNA replication depends on the correct matching of base pairs in the catalytic center of DNA replicase, assuring the error rate as low as 10-5. The extra “proofreading” exonuclease activity of DNA polymerase improves the overall accuracy by recognizing and removing the new-coming mismatched bases (down to 10-7 error rate). The following repair system (MMR) can restore the remaining mismatches efficiently. Hence the overall error rate is controlled as low as 10-9 to 10-10 error/bp.

(17) Mismatch Repair (MMR) System: Base pairs with incorrect hydrogen bonding occur spontaneously during replication process, causing distortions in the double helix of parental and daughter strands. The MutS protein in MMR system detects the distorted mismatched site and MutH identifies the erroneous daughter strand by recognizing the strand-specific methylation of adenine in GATC. MutL links MutS and H, forming a loop and promoting MutH to nick the non-methylated strand. The following Exonuclease cuts the strand from 3’ to 5’ orientation, removing the wrong base. Finally the Pol III re-synthesizes the region and the ligase fills the gap.

 

5) Thymine dimer is among the major DNA damages due to UV exposure. Name and describe several possible mechanisms that E. coli uses to repair those dimmers.

(18) (1) Direct removal by the photoreactivation catalyzed by the photolyase;

(19) (2) Nucleotide excision repair by the UvrABC system

(20) (3) Recombinational repair

(21) (4) SOS repair

Assignment: DNA & RNA

provided by Professor Dong, College of Natural Sciences, Anhui University

1) Compare the differences between DNA and RNA, structurally and functionally. Can you explain why DNA is more favorable as a genetic material?

 

2) Give your explanation about the semidiscontinuous mode of DNA replication? Can you describe the steps of replication for lagging strand?

 

3) What is an insertion element? Describe the differences between the conservative and replicative transposons.

 

4) Can you explain how to assure the fidelity of the DNA replication in bacteria?

 

5) Thymine dimer is among the major DNA damages due to UV exposure. Name and describe several possible mechanisms that E. coli uses to repair those dimmers.

 

Illustrations of wild animals [insect 10 lepidoptera]

鳞翅目Lepidoptera

Lepidoptera

Butterflies / Moths

The name Lepidoptera, derived from the Greek words“lepido” for scale and “ptera” for wings, refers to the flattened hairs (scales) that cover the body and wings of most adults.

  • Classification & Distribution

    Holometabola

    • complete development (egg, larva, pupa, adult)

    Several classification systems have been proposed for dividing the Lepidoptera into suborders. Regardless of the system used, all of the larger and more economically significant families are members of a single suborder (Frenatae or Ditrysia).

    Distribution: Common worldwide.

      North America Worldwide
    Number of Families
    75
    135
    Number of Species
    11,286
    >112,000
  • Life History & Ecology

    Lepidoptera (moths and butterflies) is the second largest order in the class Insecta.  Nearly all lepidopteran larvae are called caterpillars.  They have a well-developed head with chewing mouthparts.  In addition to three pairs of legs on the thorax, they have two to eight pairs of fleshy abdominal prolegs that are structurally different from the thoracic legs.  Most lepidopteran larvae are herbivores; some species eat foliage, some burrow into stems or roots, and some are leaf-miners.

    Adults are distinctive for their large wings (relative to body size) which are covered with minute overlapping scales.  Most entomologists believe that these scales are structurally related to the hair (setae) covering adult caddisflies.  Lepidopteran wing scales often produce distinctive color patterns that play an important role in courtship and intraspecific recognition.

    Although moths probably diverged from caddisflies in the early Triassic period, about 230 million years ago, adults in a few primitive families (e.g., Micropterygidae) still retain evidence of chewing mouthparts.  In all other lepidopteran families, the mouthparts are vestigal or form a tubular proboscis that lies coiled like a watch spring beneath the head.  This proboscis is derived from portions of the maxillae.  It uncoils by hydrostatic pressure and acts as a siphon tube for sipping liquid nutrients, such as nectar, from flowers and other substrates.

    From a taxonomic standpoint, the distinction between moths and butterflies is largely artificial — some moths are more similar to butterflies than to other moths.  As a rule, butterflies are diurnal, brightly colored, and have knobs or hooks at the tip of the antennae.  At rest, the wings are held vertically over the body.  In contrast, most (but not all) moths are nocturnal.  They are typically drab in appearance, and have thread-like, spindle-like, or comb-like antennae.  At rest, their wings are held horizontally against the substrate, folded flat over the back, or curled around the body.

  • Physical Features

    Immatures

    Adults
    • Eruciform (caterpillar-like)
    • Head capsule well-developed, with chewing mouthparts
    • Abdomen with up to 5 pairs of prolegs
    • Mouthparts form a coiled tube (proboscis) beneath the head
    • Antennal type:
      • Butterflies: knobbed or hooked at tip
      • Moths: thread-like, spindle-shaped, or comb-like
    • Front wings large, triangular; hind wings large, fan-shaped
    • Body and wings covered with small, overlapping scales
  • Major Families

    Butterflies:

    • Nymphalidae (brushfooted butterflies) — front legs reduced in size. This is the largest butterfly family; it includes the fritillaries, admirals, emperors, and tortoiseshells.
    • Danaidae (milkweed butterflies) — adults are reddish-orange with black and white markings.  Larvae feed on various species of milkweed. Includes the monarch (Danaus plexippus).
    • Pieridae (whites and sulfurs) — adults are predominantly white or yellow with black markings.  The imported cabbageworm (Pieris rapae) is a pest throughout the world.
    • Papilionidae (swallowtails) — hind wings have a tail-like extension.  The tiger swallowtail (Papilio glaucus) is a cosmopolitan species.
    • Lycaenidae (blues, coppers, and hairstreaks) — small butterflies with fluted hind wings.  Some species are extinct or nearing extinction, others are very common.
    • Hesperiidae (skippers) — antennal club is hooked at the tip.  The silverspotted skipper,Epargyreus clarus, is a common species.

Moths:

  • Tineidae (clothes moths) — some larvae construct cases and feed on natural fibers.  Pests include the webbing clothes moth (Tineola bisselliella) and the casemaking clothes moth (Tinea pellionella).
  • Gelechiidae — one of the largest families of micro-lepidoptera. These larvae feed on plants or plant products.  Pests include the Angoumois grain moth (Sitotroga cerealella) and the pink bollworm (Pectinophora gossypiella).
  • Sesiidae (clearwing moths) — diurnally active adults mimic wasps.  Many pests of fruit and vegetable crops, including the peachtree borer (Synanthedon exitiosa) and squash vine borer (Melittia cucurbitae).
  • Tortricidae — fourth largest family of Lepidoptera.  Larvae feed inside stems, leaves, and fruit.  Contains many pest species, including the codling moth (Cydia pomonella) and the oriental fruit moth (Grapholita molesta).
  • Pyralidae (snout moths) — second largest family of Lepidoptera.  Pests include the European corn borer (Ostrinia nubilalis), the Indianmeal moth (Plodia interpunctella), and the greater wax moth (Galleria mellonella).
  • Geometridae — third largest family of Lepidoptera.  Larvae are often called inchworms or spanworms.  Includes the winter moth (Operophtera brumata) and the fall cankerworm (Alsophila pometaria).
  • Lasiocampidae (lappet moths) — larvae feed on the leaves of trees and some spin large webs or tents on the foliage.  Pests include the eastern tent caterpillar (Malacosoma americana) and the forest tent caterpillar (M. disstria).
  • Saturniidae (giant silk moths) — large, colorful moths.  Larvae feed on a wide range of trees and shrubs. Well-known species include the cecropia moth (Hyalophora cecropia) and the luna moth (Actias luna).
  • Sphingidae (hawk moths) — medium to large adults with long proboscis for collecting nectar.  Larvae are frequently called hornworms.  Pests include the tobacco hornworm (Manduca sexta) and tomato hornworm (M. quinquemaculata).
  • Arctiidae (tiger moths) — distinctive adults, usually white with black, red, yellow, or orange markings.  Many larvae are covered with long hairs (woollybears).  Includes the fall webworm (Hyphantria cunea).
  • Lymantriidae (tussock moths) — larvae are characterized by tufts of hair along the body.  Adults do not feed. Pests include the gypsy moth (Lymantria dispar) and the browntail moth (Euproctis chrysorrhoea).
  • Noctuidae (loopers, owlet moths, and underwings) — this is the largest family in the Lepidoptera.  Larvae are leaf feeders and stem borers. Many species are pests, including the fall armyworm (Spodoptera frugiperda), the black cutworm (Agrotis ipsilon), and the cabbage looper (Trichoplusia ni).
Bug Bytes♣
  • Some butterflies (family Lycaenidae) are considered “endangered species”.  The Xerces blue (Glaucopsyche xerces) was last collected in 1943 from sand dunes near San Francisco, CA.  This butterfly’s name has been adopted by the Xerces Society, an organization dedicated to the preservation of endangered species.
  • In flight, front and hind wings are linked together by a bristle (frenulum) or a membranous flap (jugum) so both wings move up and down in synchrony.
  • According to folklore, larvae of the banded woollybear, Pyrrharctia isabella, can forecast the severity of winter weather.  A wide brown band means the winter will be harsh, a narrow brown band means the winter will be mild.
  • Adults of most Noctuidae and Arctiidae have “ears” in the thorax that help them detect and evade echo-locating bats.  Some species of Arctiidae even produce high-pitched ticks that confuse the bats.

====================================================

↑Quoted from the General Entomology course at North Carolina State University >Resource Library > Compendium > lepidoptera (© 2009 by John R. Meyer; Last Updated: 8 April 2009)

====================================================

Butterflies

凤蝶科Papilionidae(swallowtails)

1. 冰清绢蝶 Parnassius glacialis

2. 碧凤蝶 Papilio bianor

3. 柑橘凤蝶 Pailio xuthus

4. 金凤蝶 Pailio machaon

5. 宽尾凤蝶 Agehana elwesi.

6.青凤蝶Graphium sarpedon

7. 麝凤蝶 Byasa alcinous

灰蝶科Lycaenidae(blues, coppers, and hairstreaks)

1. 亮灰蝶Lampides boeticus

2. 琉璃灰蝶Celastrina sp.

3. 蓝灰蝶 Everes argiades

4. 红灰蝶 Lycaena phlaeas

5. 银线灰蝶Spindasis sp.

Moths

天蚕蛾科Saturniidae(giant silk moths) 

1. 合目天蚕蛾 Caligula fallax

2. 银杏天蚕蛾Dictyoploca japonica

3.长尾天蚕蛾 Actias dubernaerdi

4.樗蚕娥Philosamia cynthia

天蛾科Sphingidae(hawk moths)

1.构月天蛾Parum colligata

2. 鹰翅天蛾Ambulyx sp.

3. 紫光盾天蛾 Phyllosphingia dissimilis

灯蛾科Arctiidae(tiger moths)

1. Miltochrista ziczac

2.首丽灯蛾Callimorpha principalis

3. 红带新鹿蛾Caeneressa rubrozonat

毒蛾科Lymantridae(tussock moths)

1. 黑褐盗毒蛾Porthesia atereta

2.条毒蛾Lymantria dissoluta

the blueprint of life [11]: DNA replication 1

DNA replication

Definition: the process of copying a parental DNA molecule to form two daughter DNA molecules.

  • Introduction to DNA replication
  1. DNA replication is essential for cell proliferation, i.e. mitosis, meiosis.
  2. DNA replication is a complex endeavor involving a series of enzyme activities.→see “DNA polymerases”
  3. DNA replication is performed in a semiconservative and semidiscontinuous mode.→see “DNA replication is semi-conservative”
  4. —DNA replication has 3 stages: initiation, elongation and termination.→next section
  5. —DNA replication is tightly regulated, involving various protein-protein, protein-DNA interactions.
  6. —DNA replication of prokaryote and eukaryote shares similar features, but is distinctive in details.
  •  Chemical Reaction of DNA replication

Essentials

1. Substrate: deoxynucleoside triphosphates(dNTPs)
2. Template: a primer-template junction
       DNA is synthesized by extending the 3’ end of the primer (free 3’-OH is required)
       – RNA primer or priming from a nick in DNA
3. Enzymes: DNA polymerases etc
4. Energy supply: Hydrolysis of pyrophosphate (PPi) is the driving force for DNA synthesis
5. Ions involved: Mg++ or Zn++
  • DNA polymerases
  • DNA polymerase I—
    • Pol I was the first enzyme discovered with polymerase activity, and it is also the best characterized one.
    • —Although abundant in cells (400/cell), Pol I is NOT the primary enzyme involved with bacterial DNA replication.
    • Main functions of Pol I: — (1) Fill any gaps in the new DNA that result from the removal of the RNA primer by its 5’ -3’ polymerase activity;   (2) Remove a new mispaired base by proofreading (校读)3’-5’ exonuclease (外切酶) activity. (3)Remove the RNA primer by its 5’-3’ exonuclease activity
The 3′–>5′ exonuclease activity intrinsic to several DNA polymerases plays a primary role in genetic stability; it acts as a first line of defense in correcting DNA polymerase errors. A mismatched basepair at the primer terminus is the preferred substrate for the exonuclease activity over a correct basepair. (source)
  • DNA polymerase III
    • The primary polymerase in DNA replication, although lower in abundance (15/cell)than pol  →referred to as “replicase”
    • functions: (1) 5’→3’ polymerase activity; (2) 3’→5’ exonuclease activity – proofreading
    • Catalytic efficiency: much higher than pol I→High processivity and polymerization rate
    • A multi-unit complex: “holoenzyme” (全酶)
  • DNA replication is semi-conservative 

Bet you all have learned it in high school, and the famous experiment by Meselson and Stahl. We still need to go over the points again as they are essentially important for what we will learn next.

The key to the mechanism of DNA replication is the fact that each strand of the DNA double helix carries the same information-their base sequences are complementary (we talked about this in THE BLUEPRINT OF LIFE [2]: PRIMARY AND SECONDARY STRUCTURE OF DNA).

During replication, the two parental strands separate and each acts as a template (that’s right, the template for DNA replication is DNA itself!)to direct the enzyme-catalyzed synthesis of a new complementary daughter strand with the normal base-pairing rules (A-T, C-G)

This semi-conservative mechanism was demonstrated experimentally in 1958 by Meselson and Stahl.

Hypotheses:

In the experiment:

E. coli cells were grown for several generations in presence of the stable heavy isotope 15N so that their DNA became fully density labeled (both strands are 15N labeled: 15N/15N)

The cells were then transferred to medium containing only normal 14N and, after each cell division, DNA was prepared from a sample of the cells and analyzed on a CsCI gradient using the technique of equilibrium (isopycnic) density gradient centrifugation, which separates molecules according to differences in buoyant density.

After the first cell division, when the DNA had replicated once, it was all of hybrid density, in a position on the gradient half way between fully labled (15N /15N )and fully light (14N/14N). After the second generation in 14N, half of the DNA was hybrid density and half fully light.

Thus, two of the hypotheses were denied, left us with the semi-conservative mechanism.

After each subsequent generation, the proportion of 14N/14N increased, while some DNA of hybrid density persisted. Thus the semi-conservative mode of DNA replication is confirmed: each daughter molecule contains one parental strand and one newly-synthesized strand.

Crash Course!

Crash Course by John Green and Hank Green.

Truly truly truly great courses. Funny and easy understanding, though Hank speaks so quickly sometimes I have to rewind. : )

>>on youtube

If you are in areas where youtube cannot be reached and you don’t know how to get around the firewall:

>>on 163 open course

↑Bear with the subtitles.

 

Illustrations of wild animals [insect 9: Orthoptera]

直翅目Orthoptera

Orthoptera

Grasshoppers / Locusts / Crickets / Katydids

The name Orthoptera, derived from the Greek “ortho” meaning straight and “ptera” meaning wing, refers to the parallel-sided structure of the front wings (tegmina).

  • Classification & Distribution

    Hemimetabola

    • incomplete development (egg, nymph, adult)

    Orthopteroid

    • closely related to Blattodea and Dermaptera

    Distribution: Common and abundant throughout the world

    North America
    		 Worldwide
    Number of Families
    11
    28
    Number of Species
    1,080
    >20,000
  • Life History & Ecology

Orthoptera probably arose during the middle of the Carboniferous period.  Most living members of this order are terrestrial herbivores with modified hind legs that are adapted for jumping.

Slender, thickened front wings fold back over the abdomen to protect membranous, fan-shaped hind wings.  Many species have the ability to make and detect sounds.  Orthoptera is one of the largest and most important groups of plant-feeding insects.

  • Physical Features
    physical features image

    Adults

    Immatures
    • Antennae filiform
    • Mouthparts mandibulate, hypognathous
    • Pronotum shield like, covering much of thorax
    • Front wings narrow, leathery (tegmina); hind wings fan-like
    • Hind legs usually adapted for jumping (hind femur enlarged)
    • Tarsi 3- or 4-segmented
    • Cerci short, unsegmented
    • Structurally similar to adults
    • Developing wingpads often visible on thorax
  • Major Families

Grasshoppers and Locusts:

    • Acrididae (short-horned grasshoppers and locusts) — Herbivores.  Common in grasslands and prairies.  This family includes many pest species such as the twostriped grasshopper (Melanoplus bivittatus), the differential grasshopper (M. differentialis), the African migratory locust (Locusta migratoria), and the desert locust (Schistocerca gregaria).
    • Tetrigidae (pigmy grasshoppers) — Herbivores.  Similar to short-horned grasshoppers but with a pronotum that extends to the back of the abdomen.

Katydids:

    • Tettigoniidae (long-horned grasshoppers and katydids) — Herbivores.  Females have a long, blade-like ovipositor.  Some species are pests of trees and shrubs.

Crickets

    • Gryllidae (true crickets) — Herbivores and scavengers.  Females have a cylindrical or needle-shaped ovipositor.  This family includes the house cricket, Acheta domesticus.
    • Gryllacrididae (camel crickets) — Scavengers.  Most species have a distinctly hump-backed appearance; a few are cave dwellers.
    • Gryllotalpidae (mole crickets) — The front legs are adapted for digging.  Most species feed on the roots of plants, but some are predatory.

Bug Bytes♣

  • In many species of Orthoptera, the males use sound signals (chirping or whirring) in order to attract a mate.  The sound is produced by stridulation — rubbing the upper surface of one wing against the lower surface of another wing, or the inner surface of the hind leg against the outer surface of the front wing.
  • Each stridulating species produces a unique mating call.  In fact, some species may be so similar to each other that they can only be distinguished by their mating calls.
  • Many grasshoppers produce ultrasonic mating calls (above the range of human hearing).  In some species, the sounds may be as high as 100 kHz.  (Human hearing extends to about 20 kHz.)
  • Species that produce sound also have auditory (tympanal) organs.  In crickets and katydids, these “ears” are on the tibia of the front legs.  In grasshoppers, they are on the sides of the first abdominal segment.
  • The snowy tree cricket, Oecanthus fultoni (family Gryllidae), is often called the temperature cricket.  Adding 40 to the number of chirps it makes in 15 seconds will equal the ambient temperature in degrees Fahrenheit.
  • The redlegged grasshopper Melanoplus femurrubrum is not only a crop pest but also the intermediate host for a tapeworm Choanotaenia infundibulum that infests poultry

====================================================

↑Quoted from the General Entomology course at North Carolina State University >Resource Library > Compendium > diptera (© 2009 by John R. Meyer; Last Updated: 8 April 2009)

====================================================

剑角蝗科Acrididae(short-horned grasshoppers and locusts)

1. 中华剑角蝗 Acrida cinerea

ARIDA CINEREA
ARIDA CINEREA

2. 短翅佛蝗Phlaeoba angustidorsis

PHLAEOBA ANGUSTIDORSIS
PHLAEOBA ANGUSTIDORSIS

PHLAEOBA ANGUSTIDORSIS, nymph
PHLAEOBA ANGUSTIDORSIS, nymph

 

蚱科Tetrigidae(pigmy grasshoppers)

1. 日本蚱Tetrix japonica

TETRIX JAPONICA
TETRIX JAPONICA

2. 突眼蚱 Ergatettix dorsiferus

ERGATETTIX DORSIFERUS
ERGATETTIX DORSIFERUS

螽斯科Tettigoniidae(long-horned grasshoppers and katydids)

1. 中华尤螽Uvarovina chinensis

UVAROVINA CHINENSIS
UVAROVINA CHINENSIS

2.尤螽Uvarovina sp.

UVAROVINA SP.
UVAROVINA SP.

UVAROVINA SP., male
UVAROVINA SP., male

UVAROVINA SP. female
UVAROVINA SP. female

3. 寰螽 Atlanticus sp.

ATLANTICUS SP. female
ATLANTICUS SP. female

ATLANTICUS SP. ,male
ATLANTICUS SP. ,male

ATLANTICUS SP. ,nymph
ATLANTICUS SP. ,nymph

  1. 绿螽斯 tettigonia sp.

TETTIGONIA SP.
TETTIGONIA SP.

TETTIGONIA SP.
TETTIGONIA SP.

TETTIGONIA SP. nymph, female
TETTIGONIA SP. nymph, female

5. 斑腿栖螽Tettigonia chinensis

 

TETTIGONIA CHINENSIS
TETTIGONIA CHINENSIS

蟋蟀科Gryllidae(true crickets)

1. 斗蟀Velarifictorus sp.

VELARIFICTORUS SP.
VELARIFICTORUS SP.

2. 扁头蟋Loxoblemmus sp.

LOXOBLEMMUS SP. , female
LOXOBLEMMUS SP. , female

3. 多伊棺头蟋Loxoblemmus doenitzi

LOXOBLEMMUS DOENITIZI
LOXOBLEMMUS DOENITIZI

蟋螽科Gryllacrididae(camel crickets)

1.素色杆蟋螽Phryganogryllacris unicolor

PHRYGANOGRYLLARICS UNICOLOR, nymph
PHRYGANOGRYLLARICS UNICOLOR, nymph

DNA replication & PCR, General Biology, Open Courses at UC-Berkeley

General Biology, Great open courses given by Gary L. Firestone, Michael Meighan Jasper D. Rine and Jennifer A. Doudna, professors at UC-Berkeley.

There is more to DNA replication than we talked about yesterday so I tried to upload this video to help you learn more. 

“tried? ”

“Well, turned out ‘ DNA replication and PCR open course at Berkeley.mp4 exceeds the maximum upload size (8 MB)for this site.'”

So I would just provide the link where you can watch it online.

After watching it, maybe you will find more than just DNA replication: you may as well find how it feels going to college.

I look forward to it every time I have finished an open course online. Hope you do, too.

>>click here to watch the video

 

Public Courses

I look forward to going to college every time I have finished an open course online. Hope you do, too.

 

1. Introductory Biology 2006

2. Genetics

3. Experimental Biology and Communication

>>for more MIT open courses in biology 

 

1. Biology 1A Fall 2013

2. Biology 1B Fall 2013

>>for more Berkeley open courses in biology

 

  • Carnegie Mellon University
  1. Introduction to Biology

2. Biochemistry

3. Modern Biology

 

  • University of Alberta

Dino101(Dinosaur Paleobiology)

Genetics [10] reproduction 3: Meiosis 2

Last section we gave a general introduction of meiosis in terms of chromosome behaviors.

In this section, we will deal with two other respects of meiosis. First, a specific description of meiosis in animals; second, we will mention a situation when meiosis goes wrong.

Meiosis in animals

is found only in ovaries (卵巢)and testes(曲细精管), and even in these tissues is restricted to cells that are destined to form gametes(the germline).

Despite the fact that the mechanisms of gametogenesis differ somewhat between organisms,the steps involved in gametogenesis in mammals are relatively similar.

  • In male gametogenesis (spermgenesis).

precursors of germ cells go through many rounds of mitotic divisions in order to maintain a pool of spermatogonia(plural of spermatogonium 精原细胞).↓

Spermatogonia subsequently differentiate into primary spermatocytes(based on what you learned in high school. guess what this word mean? : D ). It is in these cells that meiosis takes place.↓

After meiosis I, these cells are referred to as secondary spermatocytes. These are haploid. The products of the second meiotic division are spermatids. ↓

Spermatids differentiate into motile spermatozoa with rounded or elongate head and a long posterior flagellum.(The final activation of spermatozoa takes place after copulation/sexual intercourse)

Without cytoplasm and many subcelluar organelles, the sperm is light and fast (almost all its weight concentrated in its head, where stored the key of a potential life, nuclei. ).

  • In female mammals, the pattern of oogenesis is superficially similar.

Here oogonia(plural of oogonium, 卵原细胞) go through mitotic divisions before differentiating into primary oocytes. These then undergo meiosis.↓

Both daughter cells of the primary oocytes are haploid but differ greatly in size. The larger daughter cell is the secondary oozyte, the smaller the first polar body. The two cells remain attached. Both undergo a second meiotic division.↓

The secondary oocyte undergoes an unequal division producing a large ovum and a small secondary polar body. The first polar body divides into two secondary polar bodies.

Only the ovum, which contains almost all the cytoplasm, will transmit genes into the next generation.

The first meiotic division is only completed at ovulation(the discharge of a mature ovum from the ovary), and the second occurs after fertilization.

Little known: In human females, primary oocytes can be held in meiotic arrest for up to 45 years. This may be important in the increased frequency of aneuploid births observed in older mothers.

Production of aneuploid gametes

The major cause of anueploidy(the situation of having or being a chromosome number that is not an exact multiple of the usually haploid number) is aberrant chromosome behavior at meiosis. In other words, it’s the failure of chromosmes to segregate properly(known as nondisjunction)

At anaphase I, if two homologous chromosomes move to the same pole, first division nondisjunction occurs. In this case, of the 4 cells arsing from meiosis, two will be disomic(contain two copies of the chromosome) and two nullisomic (contain no copy of the chromosome.

At anaphase II, if the chromatids in a cell remain together, division nondisjunction occurs. The resulting tetrad will contain two normal cells, one nullisomic, and one disomic.

Aneuploidy also arises due to nondisjunction at an early mitosis in the embryo, resulting in two populations of cytogenetically different cells in the individual, which is known as a mosaic.

MOSAIC (GENETICS)"Heterochromia iridum and iridus" image from simple.wikipedia.org
MOSAIC (GENETICS)”Heterochromia iridum and iridus” image from simple.wikipedia.org

 

Mosaic is common in Turners syndrome.

↑Turner syndrome or Ullrich–Turner syndrome is a chromosomal abnormality in which all or part of one of the sex chromosomes is absent or has other abnormalities . In some cases, the chromosome is missing in some cells but not others, a condition referred to as mosaicism or “Turner mosaicism”.

Occurring in 1 in 2000– 1 in 5000 phenotypic females, the syndrome manifests itself in a number of ways. There are characteristic physical abnormalities which affect many but not all people with Turner syndrome, such as short stature,swelling, broad chest, low hairline, low-set ears, and webbed necks. Girls with Turner syndrome typically experience gonadal dysfunction (non-working ovaries), which results in amenorrhea (absence of menstrual cycle) and sterility. Concurrent health concerns may also be present, including congenital heart disease, hypothyroidism (reduced hormone secretion by the thyroid), diabetes, vision problems, hearing concerns, and many autoimmune diseases.Finally, a specific pattern of cognitive deficits is often observed, with particular difficulties in visuospatial, mathematical, and memory areas.

Turner syndrome is named after Henry Turner, the endocrinologist who first described it in 1938.（wikipedia）