DNA Packaging and Structure

Question 1

How do prokaryotes protect their DNA/genome? What is this protection from?

Answer 1

methylation and supercoiling

methylation in particular protects from the bacteria’s own restriction enzymes

Question 2

restriction enzymes in prokaryotes chop up __1__, restrict the __2__ of viruses (whose DNA is not methylated)

Answer 2

1) DNA

2) growth

Question 3

What enzyme in prokaryotes responsible for supercoiling DNA?

Answer 3

DNA gyrase

Question 4

What proteins are eukaryotic DNA wrapped around? Which type of interactions are responsible for DNA to be wrapped around these proteins?

Answer 4

histones

electrostatic interactions

Question 5

The sugar-phosphate backbone of DNA has a slight __1__ charge, whereas the histone proteins have a __2__ charge.

Answer 5

1) negative

2) positive

Question 6

When DNA is wrapped around an _____ of histones. This is collectively called a ______

Answer 6

1) octamer (a group of 8 histones)

2) nucleosome

Question 7

The octamer is composed of 2 units each of the histone proteins. What are these proteins?

Answer 7

H2A, H2B, H3, and H4

Question 8

The string between the nucleosome beads is a length of double helical DNA called linker DNA and is bound by a single linker ______

Answer 8

histone, called H1

Question 9

Fully packed DNA is called _____

Answer 9

chromatin

Question 10

Based on your knowledge of the interactions of macromolecules and the chemical composition of DNA, do you suppose that histones are mostly basic or mostly acidic?

Answer 10

They’re mostly basic, since they must be attracted to the acidic exterior of the DNA double helix. This basicity is supplied by the AA arginine and lysine, which are unusually abundant in histones

Question 11

Complete the following flow to summarize the structure of DNA in the nucleus:

1) add a ___ to deoxyribose to form a nucleoside
2) add _____ to a nucleoside to form a nucleotide
3) polymerize a nucleotide by losing ______, which creates an oligonucleotide
4) continuation of polymerization creates a single-stranded _______
5) 2 complete chains ___ bond in antiparallel orientation to create a ds DNA chain
6) this ds DNA chain then coils to create a ds ____

Answer 11

1) base
2) 3 phosphate groups
3) 2 phosphate groups
4) polynucleotide
5) H bond
6) ds helix

Question 12

When DNA is stained, darker regions of chromosomes are called __1___, whereas lighter regions of chromosomes are called __2___.

Answer 12

1) heterochromatin

2) euchromatin

Question 13

Which regions have higher rate of transcription, heterochromatin or euchromatin?

Answer 13

euchromatin

Question 14

what is the region that binds sister chromatids together?

Answer 14

centromere

Question 15

what is the region that mitotic spindle fibers attach to during cell division?

Answer 15

centromeres

Question 16

mitotic spindle fibers attach to centromeres via _____ (multiprotein complexes that act as an anchor attachment sites for the spindle fibers).

Answer 16

kinetochores

Question 17

Centromeres are made of ____ and repetitive DNA _____

Answer 17

heterochromatin and repetitive DNA sequences

Question 18

Chromosomes have short and long arms, and the centromere position defines the ratio between the 2. What are the 3 centromere positions called?

Answer 18

Metacentric: centromere is located in the center and therefore short and long arms are in 1:1 ratio

Submetacentric: ~2:3 ratio of short to long arm

Arocentric: ~1:4 ratio of short to long arm

Telocentric: centromere is located at the top to where there are only long arms of the chromatids, no short arms are present.

Question 19

The ends of linear chromasomes are called _____

Answer 19

telomeres

Question 20

Telomeres are usually rich in which nitrogenous bases?

Answer 20

G and C

Question 21

Telomeres consist of short ___ sequences of DNA

Answer 21

repeated

Question 22

Telomeres consist of both ___ DNA and ___ DNA

Answer 22

double stranded and single stranded DNA

Question 23

Distinguish between transcription and translation?

Answer 23

transcription is the process of transcribing DNA into RNA

translation is the process of translating RNA into proteins

Question 24

For a codon, how many nucleotides make up 1 AA?

Answer 24

3

Question 25

What is the minimum amount of codons you need to synthesize all of the AA utilized in your body?

Answer 25

20

Question 26

What’s the max amount of codons that your body can possess?

Answer 26

64

Question 27

What is the start codon?

Answer 27

AUG (methionine)

Question 28

What are the 3 stop codons?

Answer 28

UAA, UGA, UAG

these do not code for AA and therefore are also considered non sense codons

Question 29

What is the only codon that codes for tryptophan?

Answer 29

UGG