Unit 05: DNA and Chromosomes

Question 1

how many base pairs are there per helical turn of a DNA double helix?

Answer 1

10 a^2

Question 2

what is the genetic code?

Answer 2

correspondence between nucleotide codons and the 20 a^2s

Question 3

each human cells contains about ___ DNA packed into a _____ nucleus

Answer 3

2m, 5-8nm

Question 4

why are chromosomes so important?

Answer 4

• prevent DNA from getting tangled
• DNA remains accessible to enzymes and proteins
• allow for compact packing of DNA

Question 5

what is chromatin?

Answer 5

complex of DNA and proteins

Question 6

are x and y chromosomes homologous?

Answer 6

no! only for cell bio tho

Question 7

how many nucleotide pairs are found in humans?

Answer 7

3.1e^9

Question 8

what are the two methods used to visualize chromosomes?

Answer 8

• paint using single stranded DNA molecules coupled w dyes
• staining chromosomes w dyes to bind to certain DNA sequence

Question 9

what is junk DNA?

Answer 9

non coding DNA between and within genes!

Question 10

what is junk DNA within a gene called?

Answer 10

an intron

Question 11

is junk DNA highly conserved?

Answer 11

yes!

Question 12

at any position on DNA are there genes on the exact same places on both strands?

Answer 12

no

Question 13

what is roughly correlated with species complexity?

Answer 13

gene number

Question 14

many less complex organisms that have many chromosomes have lots of ______ chromosomes

Answer 14

small

Question 15

what are chromosomes in interphase doing?

Answer 15

partly preparing for cell division, but mostly just doing their normal cell functions

Question 16

are interphase chromosomes or mitotic chromosomes longer and finer?

Answer 16

interphase

Question 17

what are the two classes of proteins associated with DNA?

Answer 17

histones and non-histones

Question 18

are there more types of histones or non histones?

Answer 18

non histones

Question 19

the mass of histones in a cell is approximately _____ to the mass of DNA

Answer 19

equal

Question 20

what is the first and most fundamental level of chromatin packaging?

Answer 20

nucleosomes

Question 21

nucleosomes convert DNA to____

Answer 21

a fiber 1/3 the length of the original DNA

Question 22

what is the result of chemical treatments to nucleosomes?

Answer 22

condensation of H1 histone to get separation giving beads on a string appearance

Question 23

what is linker DNA?

Answer 23

the exposed DNA between core particles of nucleosomes

Question 24

how many histones are in an octamer?

Answer 24

8

Question 25

what are the histones in an octamer?

Answer 25

2 each of H2A, H2B, H3, H4

Question 26

what does each histone in an octamer have?

Answer 26

long, unstructured N-terminus a^2 tail

Question 27

within an octamer histone, positively charged ____ and ______ bind negatively charged DNA

Answer 27

lysine, arginine

Question 28

is a histone coil left or right handed?

Answer 28

left!

Question 29

how many a^2 does it take for a turn in a histone coil?

Answer 29

1.7

Question 30

what is histone H1?

Answer 30

a linker histone that changes path DNA takes as it exits nucleosome

Question 31

how does the H1 histone change the path of DNA?

Answer 31

by pulling adjacent nucleosomes tgt, condensing the fiber

Question 32

what is a looped domain?

Answer 32

when the chromatin is packed into a series of loops that extend from the center of the chromosome

Question 33

what are SMC proteins?

Answer 33

protein complexes that travel along DNA via ATP hydrolysis to create loop

Question 34

what is cohesin?

Answer 34

an SMC protein complex that organizes structure of interphase chromosomes. first round of large looping

Question 35

what are sequence specific clamp proteins?

Answer 35

proteins that stop/stall cohesin by binding to e/o, drawing DNA tgt at base of loop, preventing loop from getting too big

Question 36

what are condensins?

Answer 36

SMC ring proteins that replace cohesins that use ATP hydrolysis to form even more loops within loops, packing the DNA into a tighter mass of coils

Question 37

what are ATP dependent chromatin remodeling complexes?

Answer 37

protein complexes that use ATP hydrolysis to shift nucleosomes side to side along the DNA. it makes DNA more/less accessible to other proteins

Question 38

per how many nucleosomes is an ATP dependent chromatin remodeling complex?

Answer 38

5 nucleosomes

Question 39

what are histone-modifying enzymes?

Answer 39

enzymes attatched to the unstructured, N-terminal end of the amino acid tail of histones that regulate the addition and removal of acetyl, phosphate and methyl groups.

Question 40

what else do histone-modifying enzymes affect?

Answer 40

- how tightly DNA is packed - docking site for regulatory proteins - spreads along DNA until barrier sequence reached

Question 41

inappropriate packing causes _____

Answer 41

disease

Question 42

what is an example of inappropriate packing causing disease?

Answer 42

a deleted barrier sequence causes the beta globin gene to deactivate since it is packed super tight. this causes anemia.

Question 43

can each piece of chromatin only heterochromatin or euchromatin?

Answer 43

no! each chromatin has hetero and euchromatin segments!

Question 44

what is heterochromatin?

Answer 44

the most highly condensed form of chromatin

Question 45

what makes up 40% of interphase chromatin?

Answer 45

heterochromatin

Question 46

half of heterochromatin is permanently condensed, meaning there is no gene expression. what regions are these?

Answer 46

regions around centromeres and telomeres

Question 47

what is euchromatin?

Answer 47

least condensed form of chromatin

Question 48

how much of the human genome is in euchromatin all the time?

Answer 48

20%

Question 49

can gene expression be turned in in euchromatin?

Answer 49

yes!

Question 50

is gene expression on in heterochromatin?

Answer 50

no

Question 51

what is epigenetic inheritance?

Answer 51

transmission of traits based on factors not related to nucleotide sequence

Question 52

describe how heterochromatin structure is passed down from parent to daughter.

Answer 52

1. during DNA replication, daughter strand receives half of parent's histones which contain the parent's modifications. 2. histone markers are spread to adjacent histones 3. heterochromatin now spreads to match the parent DNA