1.14. Organization of genetic information

Question 1

both pro- and eukaryotes use DNA as…
(the only exception…)

Answer 1

genetic material, but there are differences in their DNA organization
retroviruses (using RNA)

Question 2

location and number of DNA molecules (p vs e)

Answer 2

prokaryotes:
- in the nucleoid, 1 circular DNA (no. of DNA mol. equal to the number of chromosomes)
eukaryotes:
- in the nucleoplasm/nucleus, 2 or more linear DNA (always even number)

Question 3

types of DNA sequences (p vs e)

Answer 3

prokaryotes:
- the majority of the DNA codes for proteins except for regulatory sequences (promotors, terminators…) + codes for rRNA/tRNA
- coding sequences not interrupted by non-coding
eukaryotes:
- coding regions make up only a smart portion of the genome, the rest is non-coding (in humans taking up 97% ), coding regions are composed of introns and exons

Question 4

association with proteins (p vs e)

Answer 4

prokaryotes:
- “naked” - not joined with proteins
eukaryotes:
- associated with globular proteins called histones which control the gene expression

Question 5

mitosis (natural process of cloning) preserves

Answer 5

the genom

Question 6

histones

Answer 6

• globular proteins associated with the DNA in eukaryotes
• the DNA coils around them and condenses/supercoils, forming chromosomes (they provide the structure to the chromosome)
• soluble in water
• contribute to gene expression

Question 7

types of non-coding sequences

Answer 7

1|regulatory sequence
2|introns
3|short tandem repeat sequences (STR seq.)
4|codes for tRNA and rRNA
- they can code for anything but proteins (only coding parts of DNA code for proteins)

Question 8

STR seq. and regulatory sequences are in the ____ of the DNA (__), and introns are in the ___ of the DNA but…

Answer 8

non-coding part, not a part of a gene, coding part, they get spliced out (not in the mature mRNA) - they don’t code for anything

Question 9

short tandem repeat sequences

Answer 9

• not a part of the gene (non-coding DNA)
• composed of repeating units (5-300 bp long) that repeat as many as 100 000x along the DNA)
• unique for every single person (size and sequence differ) - STR analysis the basis for DNA fingerprinting
• can afford to mutate - doesn’t code for anything - while e.g. insulin gene has to be the same in all people for it to perform its function (it would decrease the “quality” of the organism - evolutionary speaking)

Question 10

regulatory sequences

Answer 10

promotors and terminators - on the DNA but don’t get transcribed (non-coding, have a regulatory function)

Question 11

Where are STR seq. mainly found

Answer 11

in centromeric and telomeric regions of the chromosome

Question 12

what happens to the DNA length in DNA replication

Answer 12

terminal (end) segments of the DNA (3’ to which RNA primers attached) are lost as no DNA nucleotides can attach to the 5’
- this is why no coding parts of the DNA on the ends

Question 13

telomerases

Answer 13

STR sequences on the DNA ends - they have a protective function for the DNA - get lost during DNA replication and once they are used up that DNA can never replicate again (otherwise would lose genes) - cell dies

Question 14

genes for tRNA and rRNA

Answer 14

stretches of DNA that are transcribed into mRNA but aren’t translated (4th non-coding type of sequence)

Question 15

alternative splicing

Answer 15

one gene can encode for more than one protein

Question 16

telomerase

Answer 16

recovering telomers (cancer cells have a lot of it so they are capable of counless divisons)

Question 17

nucleosome =

Answer 17

8 histones + 2 turns of the DNA around them

Question 18

What prevents the DNA strand from entangling and breaking (leading to mutation)?

Answer 18

formation of nucleosomes, that is, the beads on a string structure

Question 19

how do histones regulate gene expression

Answer 19

genes in condensed/supercoiled DNA (coiled around histones) are not approachable to transcription enzymes (RNA polymerase) therefore no gene expression

Question 20

histone N-terminal tails

Answer 20

link together and pull nucleosomes together which provide further stabilization of the condensation - protruding from each histon

Question 21

linker DNA

Answer 21

short DNA section that links 2 nucleosomes

Question 22

H1 histone

Answer 22

binds the DNA to the core of nucleosome, stabilizing its condensation

Question 23

draw a complex of 2 nucleosomes

Answer 23

…

Question 24

acetyl group (with and without)
- acetic acids (CH3-COO^-)

Answer 24

• abundant in the nucleus
• with AC - histone tails don’t join together, don’t pull histones closer so level of DNA condensation decreased, increasing gene expression
• without AC (normal) - histones pulled together, higher level of DNA condensation, reduction in gene expression
• it impacts the conformation of histone tails and therefore impacts the expression of genes

Question 25

modification of histone tails by acetyl groups

Answer 25

acetylation