BCHM-3050 Lecture Notes - Lecture 4: Human Genome Project, Noncoding Dna, Post-Translational Modification

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26 Jun 2018

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Chapter 21: Genes, Genomes, and Chromosomes

Overview

Genes – single polypeptide chain

Genome – total genetic information

Chromatin – DNA inside with histones and then chromatin becomes a chromatid.

Packaging of Eukaryotic DNA

Bacteria use negative supercoiling and eukaryotic DNA is confined to the nucleus and

wrapped around histone proteins.

In bacteria, the compaction of DNA is done via negative supercoiling and made into a

nucleoid, which is NOT membrane-bound.

oThe nucleoid exists in the cytosol and is attached via ribosomes.

oBacteria have only 1 chromosome per cell and eukaryotes are diploid

Eukaryotes have introns which are the noncoding segments.

Size of Human Genome

There is junk DNA (introns, viral, repeats, etc.) and the noncoding region have important

functions (just unknown right now)

The Human Genome Project costs $400 million

Kinetics

E. coli have only ONE copy and they re-associate slowly, while eukaryotic DNA have 2

steps (slow & fast)

oSlow Step = non-repeated sequences

oFast Step = repeated sequences

Chromosome Features

2 chromatids are joined via a centromere to make a chromosome

DNA is the length of 2m. and there are regularly spaced points on the DNA

Nucleosomes = portions of DNA that CANNOT be digested. It includes both DNA and

proteins.

oTelomeres are guanine-rich DNA repeat sequences (TTAGGG) that protect the

end of the DNA from degradation. They ensure that each chromosome is copied

completely.

oThere are 2 copies of each histone protein for every 1 nucleosome.

Structures and Properties of Chromsomes

Post-translational modification of the K/R decreases affinity for DNA/RNA

Chromatin during interphase has 2 forms:

oEuchromatin – transcriptionally ACTIVE

oHeterochromatin – much thicker and INACTIVE

Chromosome neighborhoods are regions of DNA that are far apart linearly, but close

together in 3-D space that may lead to cross linking.

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Document Summary

Chromatin dna inside with histones and then chromatin becomes a chromatid. Bacteria use negative supercoiling and eukaryotic dna is confined to the nucleus and wrapped around histone proteins. Eukaryotes have introns which are the noncoding segments. There is junk dna (introns, viral, repeats, etc. ) and the noncoding region have important functions (just unknown right now) The human genome project costs million. E. coli have only one copy and they re-associate slowly, while eukaryotic dna have 2 steps (slow & fast: slow step = non-repeated sequences, fast step = repeated sequences. 2 chromatids are joined via a centromere to make a chromosome. Dna is the length of 2m. and there are regularly spaced points on the dna. Nucleosomes = portions of dna that cannot be digested. It includes both dna and proteins: telomeres are guanine-rich dna repeat sequences (ttaggg) that protect the end of the dna from degradation.

Related Questions

The bacterium E. coli, which is a major model system for the study of genes and DNA, has a singular circular chromosome of about 4x106 bp. In contrast, human diploid cells have __1__ chromosomes, of __2__ different types (donât forget that the X Â¹ Y!). The total amount of DNA found in a haploid cell such as a sperm or egg is called the organismâs âC-valueâ; the human C-value is __3__.

Also in contrast to the E. coli circular chromosome is the fact that eukaryotic chromosomes are not circular, but instead are __4__. Eukaryotic chromosomes are complexed heavily with protein to form a DNA-protein complex generically called __5__. The proteins found can be considered to fall into two general classes: __6__ and __7__. The first class is made up of 5 major proteins called __8__, __9__, __10__, __11__, and __12__. On a weight to weight basis, these proteins make up about __13__% of the total mass of a chromosome. Since these proteins must associate relatively non-specifically with DNA, they are rich in the basic amino acids __13__ and __14__, which gives the proteins a net __15__ charge.

One goal of packaging the DNA into chromatin is to compact the genome so it will fit into a nucleus. The basic unit of chromatin structure is the __16__, which has __17__ base pairs of DNA wrapped around a âcore particleâ composed of __18__ copies each of the core histones. Each nucleosome is separated by a stretch of âlinkerâ DNA so that the repeating unit is approximately 200 bp. Lets do a little arithmetic: If we consider that the nucleosome is approximately __19__ nm in diameter, that there is about 200 bp in this structure, and that 200 bp of DNA would normally occupy __20__ nm if stretched out straight (recall that each base is spaced about 0.34 nm from the next), we can see that the nucleosome alone allows for a __21__-fold compaction ratio.

The nucleosome structure is further compacted by histone __22__, which is not a part of the core particle. Instead, this histone __23__ (does what?) to cause the nucleosomal 10 nm fiber to condense into a higher-order structure referred to as the __24__ nm fiber. In the nucleus, chromosomes do not just float around freely: they are tethered to a proteinaceous structure called the __25__ at specific DNA regions called âSARsâ, which stands for __26__. SARs are rich in topoisomerases, to allow the winding and unwinding of the DNA that accompanies replication and transcription to occur, despite this constraint.

The 30 nm fiber discussed above is the form in which transcriptionally active DNA is believed to exist in the nucleus; however, further condensation leads to a highly condensed inactive form called __27__; in this terminology, the active form is referred to as __28__. The inactive condensed form can be divided into two types: one type is essentially invariant between cell types, and since it is âon all t timeâ, it is referred to as __29__. The other type comes and goes, depending on the expression of the genes present in that region of the chromosome; it is referred to as __30__.

Eukaryotic chromosomes carry the genes, of course, but also have other functional regions. One such region is the place where the spindle apparatus attaches during mitosis and meiosis; this region of the chromosome is called the __31__. Another important part of the linear eukaryotic chromosome is the ends; these are called __32__. In humans, the end of each chromosome is composed of many repeats of the short sequence __33__. One more type of functional region on each chromosome is the place where DNA replication starts; in humans, each chromosome has several of these __34__. Thus, eukaryotic chromosomes carry several different types of functional sequences, which together allow for their __35__ during S phase, __36__ during mitosis and meiosis, and the __37__ of their genes

Please provide correct answer and explanation to the answer,Thank you!

If an enterprising graduate student decided to repeat theHershey-Chase

experiment but neglected to perform the blending portion, wherewill the

isotopes be found?

a. 35S will be found in the supernatant and 32P will be found inthe pellet

b. 32P will be found in the supernatant and 35S will be found inthe pellet

c. Both 32P and 35S will be found in the supernatant

d. Both 32P and 35S will be found in the pellet

e. None of the above are correct
Chargaffï¿½s rules include:

a. The ratio of Aï¿½s + Tï¿½s to Gï¿½s + Cï¿½s is always consistent

b. A=G and T=C

c. Purines/Pyrimidines = 1

d. More than one of the above are true

e. None of the above are true
Sea Urchin DNA contains 18% guanine (which is true); how muchthymine

does it contain?

a. 9%

b. 18%

c. 32%

d. 36%

e. 64%
E. coli DNA contains a little over 25% guanine. If samples weretaken of E.

coli DNA and Sea Urchin DNA and denatured in water baths, whichwould

melt at a lower temperature?

a. E. coli DNA

b. Sea Urchin DNA

c. They would melt at the same temperature

d. There is not enough information to determine the answer

e. DNA doesnï¿½t ï¿½melt,ï¿½ it isnï¿½t ice cream for goodness sake!
If testing the second generation results in tube B, which modelcan we

conclude is correct?

a. Dispersive

b. Semi-conservative

c. Conservative

d. Semi-dispersive

e. We canï¿½t conclude yet, it could still be more than onepossibility
Phosphorus is required to synthesize dNTPs used in DNAreplication. Imagine

you grow E. coli in media containing non-radioactive phosphorusfor many

generations, then switch the E. coli to media containingradioactive

phosphorous (32P). You then sample the E. coli after one roundof replication

for radioactivity. Where will you find radioactive phosphorus inthe DNA?

a. Both strands will contain 32P

b. One strand will contain 32P

c. Neither strand will contain 32P

d. Drats! I knew I should have done suggested problem 12.19!
Which of the following statements about chromosomes are alwaystrue?

I. Non-histone proteins make up about 5% of a eukaryotic

chromosome by weight

II. Histones have a negative charge

III. Prokaryotes have a single linear chromosome

a. Only Statement I is true

b. Only Statement II is true

c. Only Statement III is true

d. More than one of the above statements are true

e. None of the above statements are true
What portion of the human genome is made up of highly repetitiveDNA?

a. Less than 5%

b. 6 ï¿½ 20%

c. 21 ï¿½ 30%

d. 31 ï¿½ 40%

e. Over 40%
Which of the following statements are always true?

I. Histones are very conserved between species

II. Archaea have nuclei

III. Prokaryotes are haploid and eukaryotes are diploid

a. Only Statement I is true

b. Only Statement II is true

c. Only Statement III is true

d. More than one of the above statements are true

e. None of the above statements are true
An individualï¿½s phenotype is a function of:

a. The alleles they carry

b. The environment they live in

c. The interaction between an individuals genes and theenvironment

d. Two of the above are correct

e. All of the above are correct
A homologous pair of chromosomes showing a

crossover are shown to the right for reference. Are all

the sperm from one human male genetically identical?

a. Yes

b. No, variation occurs during mitosis

c. No, variation occurs during meiosis I

d. No, variation occurs during meiosis II

e. No, variation occurs during both meiosis I and II
Production of gametes in humans requires which kind ofdivision?

a. Meiotic and is reductional

b. Mitotic and is reductional

c. Meiotic and is equational

d. Mitotic and is equational

e. None of the above

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BCHM-3050 Lecture Notes - Lecture 4: Human Genome Project, Noncoding Dna, Post-Translational Modification

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