Genetics Exam 3

Question 1

ultimate storage problem

Answer 1

being able to pack a lot of DNA into a cell

Question 2

how long would the DNA of a human cell measure?

Answer 2

2m (over 6ft)

Question 3

hierarchical levels of DNA structure

Answer 3

primary structure: nucleotide sequence
2ndary: double-stranded helix
tertiary: higher-order folding (allows DNA to be packed into cell)

Question 4

supercoiling

Answer 4

tertiary structure; forms when DNA is strained from over or under rotation; circular or looped DNA

Question 5

relaxed state

Answer 5

no strain; lowest energy state; 10 bp per turn

Question 6

positive supercoiling

Answer 6

overrotation; (compared to relaxed state) less base pairs per turn

Question 7

negative supercoiling

Answer 7

underrotation: (compared to relaxed state) more bp per turn; most DNA

Question 8

topoisomerases

Answer 8

enzyme; adds/removes rotations; temporarily breaks nucleotide strand –> rotates ends around each other –> rejoins ends; not all can induce and relieve supercoiling

Question 9

advantages of negative supercoiling (over relaxed)

Answer 9

easier to separate strands during replication and transcription (faster and requires less energy); supercoiled can be packed into smaller spaces than relaxed

Question 10

difference of bacterial chromosome (from eukaryotic)

Answer 10

(usually) circular; no histones; other proteins compact it

Question 11

nucleoid

Answer 11

bacterial DNA confined to a definite region of the cytoplasm; appears as a distinct clump

Question 12

difference of eukaryotic chromosomes

Answer 12

(usually) linear; a lot of DNA; histones to help pack

Question 13

chromatin

Answer 13

complex of DNA and proteins; 2 types

Question 14

euchromatin

Answer 14

goes through normal process of condensation and decondensation during cell cycle

Question 15

heterochromatin

Answer 15

stays condensed throughout cell cycle; 2 types

Question 16

constitutive heterochromatin

Answer 16

permanent; telomeres, centromeres, Y chromosome (consists largely of)

Question 17

facultative heterochromatin

Answer 17

occurs during certain developmental stages; inactivated X

Question 18

histones

Answer 18

small, positively charged proteins; 5 major types (H1, H2A, H2B, H3, H4); high % of arginine and lysine

Question 19

variant histones

Answer 19

somewhat different amino acid sequence; can replace one of the major histone types; alter chromatin structure and influence function

Question 20

nucleosome

Answer 20

simplest level of chromatin structure; DNA wrapped 2 times around octamer of histone proteins

Question 21

nucleosome “tail”

Answer 21

11-37 amino acids that extend from nucleosome; + charged aa interact with (-) charge of DAN phosphates, keep

Question 22

how much DNA is in direct contact with the histone octamer?

Answer 22

145-147bp

Question 23

which type of histone is not part of the nucleosome?

Answer 23

H1

Question 24

how many bp does the entire nucleosome encompass?

Answer 24

~167bp

Question 25

linker DNA

Answer 25

stretch of DNA separating 2 nucleosomes; varies in size among cell types (for most cells:~30-40bp)

Question 26

histones in archaea?

Answer 26

2 types similar to H3 and H4; associate in groups of 4 (tetramers)

Question 27

how many bp of DNA does archaeal nucleosomes?

Answer 27

60-500 bp

Question 28

higher order chromatin structure

Answer 28

30nm wide fiber; different structures of the fiber have been proposed (look in textbook)

Question 29

loop extrusion

Answer 29

how loops of chromatin are formed; carried out by SMC complex; formation of topologically associating domains

Question 30

structural maintenance of chromosomes (SMC) complexes

Answer 30

includes condensin and cohesin; role in chromosome structure and gene expression;

Question 31

condensin

Answer 31

helps condense DNA during mitosis and meosis

Question 32

cohesin

Answer 32

holds sister chromatids together

Question 33

topologically associating domains (TADs)

Answer 33

large regions of spatially interacting chromatin; forms during interphase; within TADs chromatins lie in close proximity, but TADs are separated from other TADs; important role in gene regulation