Biology 1201A Lecture Notes - Lecture 3: Centromere, Melanin, Homologous Chromosome

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olivewombat473

5 Oct 2015

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Homework is to answer the question -> give answer to jennifer waugh. Genome size (c-value) the amount of dna in one genome (eg. one complete set of chromosomes). When calculating genome size it is (mb) a count of how many nucleotides that exist, this stands for megabases , his is the base pairs. (pg) picograms measures the weight. *there is no real way to connect the type of organism or complexity to the amount of dna they have. (eg. rice has more dna than a fruit y) C-value paradox something that occurs but doesn"t make sense, there is the understanding that things are complex and vary in complexity. But there is so much variation in the amount of dna in comparison to others. Mice vs. human smaller body with more genomes than human, humans have lots of bases but they are not all used.

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Ploidy refers to the number of complete sets of chromosomes (genes) present in a cell. The number of chromosomes in a complete set is a fixed characteristic of a species. Humans are diploid with two sets of 23 chromosomes. Fruit flies are diploid with two sets of 4 chromosomes. Sexually reproducing organisms are diploid, each somatic cell of an organism has two complete sets ("di" is a prefix indicating 2.). To complete a life cycle and reproduce new members of a species, mating is required. Mating brings a donation from a male and a donation from a female together. However, if the male and female cells remain diploid, the fertilization will result in a tetraploid zygote. In general, these are not viable. A mechanism is needed to form special haploid cells, gametes. The diploid set is split precisely into two complete haploid sets. That mechanism is meiosis.

The complete set of chromosomes of a species is also the complete set of genes of a species, the genome. (Yes, there is a minor contribution from mitochondria and chloroplasts. Inheritance of this information is "cytoplasmic".)

Please answer the following questions:

1. How many chromosomes in a brain cell of a fruit fly? How many chromosomes are in a liver cell of a human? Explain both answers.

2. How many chromosomes are in a fruit fly unfertilized egg? How many chromosomes are in a human egg? Explain both answers.

3. Why is meiosis necessary for sexually reproducing organisms? How many chromosomes are in a human zygote? Relate the two answers.

4. What is a gene allele? Suppose there is a gene called "bingo" and it is present once in a complete haploid set. How many alleles of "bingo" does a diploid individual have? How many copies or versions of the gene "bingo" are present in a diploid individual?

5. Modern DNA sequencing clearly identifies alleles by showing the different DNA sequence of each allele. These alleles may be termed structural alleles (I coined the term for this problem.). Classical genetics only dealt with phenotypes or visible traits. As a result, alleles of genes were identified by functionality, usually normal or non-functional. Using your knowledge of gene structure and gene expression, postulate a relationship between structural alleles and functional alleles. (include relative amounts; more, less, or equal).

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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Biology 1201A Lecture Notes - Lecture 3: Centromere, Melanin, Homologous Chromosome

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