DNA Structure & Replication

Question 1

what is a nucleotide monomer made of?

Answer 1

a phosphate group, ribose, nitrogenous base

Question 2

which nucleotides are purines?

Answer 2

adenosine & guanosine

Question 3

which nucleotides are pyrimidines?

Answer 3

thymidine & cytidine

Question 4

how are single strands of DNA formed?

Answer 4

connecting nucleotides via covalent bonds from the phosphate groups to the deoxyribose sugars

Question 5

within our body, when is DNA single stranded and not double stranded?

Answer 5

during replication

Question 6

what does it mean for DNA to be “anti-parallel”

Answer 6

single strands are upside down compared to eachother, 5’ and 3’ ends are opposite from one another

Question 7

how are single strands bound in double-stranded DNA?

Answer 7

by many weak hydrogen bonds between nitrogenous bases

Question 8

what is “base-pairing”

Answer 8

binding between specific nucleotides

Question 9

which base-pair is easier to break? G-C or A-T?

Answer 9

A-T (2 hydrogen bonds) whereas G-C has 3

Question 10

describe the Watson and Crick “semi-conservative model” for DNa replication

Answer 10

double stranded DNA parent strand is separated into two single strands, each of which is used as a template to synthesize another strand of DNA, the resulting daughter DNA molecules consist of one parent strand and one newly synthesized strand

Question 11

Double stranded DNA molecules are wrapped up with proteins inside the cell in order to form what structures?

Answer 11

chromosomes

Question 12

What phase does DNA replication occur during?

Answer 12

interphase

Question 13

What structures does DNA replication result in?

Answer 13

two sister chromatids

Question 14

Where does DNA replication start? What does this create?

Answer 14

at multiple origins of replication, creating replication bubbles

Question 15

What is the purpose of having multiple origins of replication?

Answer 15

makes replication go significantly faster, it is more efficient

Question 16

purpose of helicase

Answer 16

separates dsDNA into single strands at the origin of replication

Question 17

purpose of single strand binding protein

Answer 17

keeps strands apart and prevent rewinding of the double helix

Question 18

purpose of topoisomerase

Answer 18

releases mechanical stress in front of helicase

Question 19

purpose of primase

Answer 19

makes the RNA primer (small section of dsDNA) that allows the DNA polymerase to start synthesizing

Question 20

how is the RNA primer removed

Answer 20

via a nuclease

Question 21

How does DNA polymerase add nucleotides?

Answer 21

creates a new covalent bond between the last deoxyribose sugar group and the phosphate group of a free floating nucleotide monomer

Question 22

How is the leading strand synthesized?

Answer 22

continuously in the 5’ to 3’ direction

Question 23

How is the lagging strand synthesized?

Answer 23

in Okazaki fragments because DNA polymerase can only synthesize in the 5’ to 3’ direction, uses multiple RNA primers that the DNA polymerase jumps to

Question 24

How many base pairs in the human genome?

Answer 24

3.1 billion

Question 25

What is a byte? What is a bit?

Answer 25

byte = 8 bits bit = one digital piece of info (0 or 1)

Question 26

How many bits are needed to encode (A, T, C, G)?

Answer 26

Two: A(0,0) T(0,1) C(1,0) G(1,1)

Question 27

How many GB in the human genome?

Answer 27

0.775 GB (7 powerpoints)

Question 28

How does DNA polymerase detect errors?

Answer 28

mismatch is sensed as a bulge, DNA polymerase backs up and breaks the covalent bond cutting out incorrect nucleotide, then DNA polymerase resynthesizes correct nucleotide

Question 29

If DNA polymerase doesn’t catch the errors, what enzyme does?

Answer 29

nucleases cut out incorrect nucleotides and DNA polymerase resynthesizes

Question 30

structure of dsDNA of prokaryotes

Answer 30

circular

Question 31

structure of dsDNA in eukaryotes

Answer 31

linear

Question 32

How do eukaryotes solve the issue of a 3’ overhang after a round of replication?

Answer 32

telomerase uses its own RNA template to extend the 3’ end and then DNA polymerase can make a new Okazaki fragment

Question 33

What happens to telomere length as humans age?

Answer 33

telomere length declines due to decreased telomerase activity, which increases mortality

Question 34

What problem does having short telomeres present?

Answer 34

ends of telomeres can’t form protective T loop, the cell detects the free end as a dsDNA break and so it puts a stop to cell division and the cell gets old

Question 35

Which strand poses the 3’ overhang issue?

Answer 35

lagging strand

Question 36

which enzyme connects the Okazaki fragments of the lagging strand?

Answer 36

ligase