DNA Replication

Question 1

What is DNA composed of?

Answer 1

nucleotides

Question 2

What are nucleotides composed of?

Answer 2

pentose sugar, phosphate group, nitrogenous base

Question 3

What is the difference in the sugar of DNA and RNA?

Answer 3

DNA has deoxyribose sugar (no OH group)

RNA has ribose sugar (has OH group)

Question 4

What is the difference between purines and pyrimidines?

Answer 4

purines are double ring, pyrimidines are single ring

Question 5

How are nucleotides linked? What type of reaction is this?

Answer 5

phosphodiester bonds

condensation

Question 6

What is the structure of DNA? How are strands arranged?

Answer 6

double helix, antiparallel

Question 7

What is the inside vs the outside of the double helix?

Answer 7

inside in nitrogenous bases, outside is sugar phosphate backbone

Question 8

Why do purines only pair with pyrimidines?

Answer 8

because if two purines, not enough room and two pyrimidines, too much room

Question 9

Is an adenine-thymine bond stronger than a cytosine-guanine bond? Why?

Answer 9

No, C-G is stronger

three hydrogen bonds and A-T only has 2

Question 10

What is antiparallel?

Answer 10

5’ end of one strand aligns with 3’ end of other strand of DNA

Question 11

What is chromatin?

Answer 11

mixture of DNA and associated proteins

Question 12

What are histones?

Answer 12

proteins that DNA wrap around in order to fit into the nucleus

Question 13

What is euchromatin? What does it mean?

Answer 13

loosely packed DNA

transcription is occurring (genes are expressed)

Question 14

What is heterochromatin? What does it mean?

Answer 14

tightly packed DNA

transcription is not occurring (genes are not expressed)

Question 15

What is semiconservative DNA replication mean?

Answer 15

each newly made strand is composed of one parent strand (old) and one daughter strand (new)

Question 16

What are chromosomes?

Answer 16

Nuclear units of genetic information that are divided
and distributed by cell division.

Question 17

Why is replication of DNA important for the cell cycle?

Answer 17

ensures that each daughter cells gets the same DNA as parent cell

Question 18

What is the origin of replication?

Answer 18

sequence of DNA (mostly A-T bonds) where replication is initiated

Question 19

How many times is DNA replicated? Why?

Answer 19

once

too much energy, and cells would get too much DNA

Question 20

What is a replication bubble?

Answer 20

area of unwound and open dna

Question 21

What is a replication fork?

Answer 21

ends of the replication bubble where DNA is still in double helix

Question 22

What is helicase?

Answer 22

enzyme that unwinds and separates the DNA strands at the Replication Forks

Question 23

What is single strand binding proteins? (SSBS)

Answer 23

Proteins that stabilize separated strands by preventing them from rebinding to eachother

Question 24

What is topoisomerase?

Answer 24

Relieves twisting pressure on still-wound DNA ahead of the replication fork by making small cuts in the backbone

Question 25

Can DNA polymerase bind anywhere on the template strand?

Answer 25

no it needs a starting point (primer)

Question 26

What are RNA primers? What creates them?

Answer 26

starting point for DNA polymerase to start building from primase

Question 27

What is DNA polymerase III? Where does it start from?

Answer 27

catalyze the addition of nucleotides to the template strand in a complementary manner 3' end of RNA primer

Question 28

What direction is DNA created? What direction is parent strand read?

Answer 28

5' to 3' direction 3' to 5' direction

Question 29

What does the sliding clamp of DNA polymerase do?

Answer 29

keeps attached to DNA strand until replication is finished

Question 30

What strand does DNA polymerase add bases to?

Answer 30

both template strands

Question 31

What are three rules of DNA replication?

Answer 31

1. always elongates from a 3' end 2. always add bases in a complementary manner 3. leading strand, polymerase moves towards fork, lagging strand, polymerase moves away from fork

Question 32

What is the leading strand?

Answer 32

elongates towards the replication fork, continuous, only one primer needed, begins from 3' end of rna primer

Question 33

What is the lagging strand?

Answer 33

elongation away from replication fork, not continuous, multiple primers needed, begins from 3' end of primer

Question 34

What are Okazaki fragments?

Answer 34

fragments of dna created on lagging strand

Question 35

What is DNA polymerase I?

Answer 35

removes RNA primers and replaces them with DNA nucleotides

Question 36

What attaches okazaki fragments together?

Answer 36

DNA ligase by linking the sugar-phosphates (phosphodiester bonds)

Question 37

What happens to eukaryotic DNA after replication? Why?

Answer 37

it gets shorter 5' end of complementary DNA cannot be completed because DNA polymerase always needs a 3’ end to work from

Question 38

Does DNA loss occur in circular bacterial DNA?

Answer 38

no

Question 39

How is gene loss prevented?

Answer 39

Non-coding DNA called telomere is at end of DNA (5’TTAGGG3’) telomeres are removed instead of coding dna

Question 40

What is telomerase? Where is it active? Why?

Answer 40

catalyzes the lengthening of telomeres germ cells (sperm/egg) these genes are passed to offspring, not as active in somatic cells because they die instead

Question 41

How does telomerase extend?

Answer 41

by adding telomere sequence repeats to the 3’ end Carries an RNA template and has reverse transcriptase activity (RNA to DNA)

Question 42

How is some kinds of cancer linked to telomerase?

Answer 42

DNA will not shorten and therefore not die leading to uncontrolled cell division

Question 43

What happens when telomeres get short and eventually coding DNA is not replicated?

Answer 43

cell death

Question 44

What are mutations? How are they caused?

Answer 44

errors in replication or DNA damage natural/synthetic chemicals, radioactivity, x-rays, UV

Question 45

What is a thymine dimer?

Answer 45

UV light can cause adjacent thymines to bind and create a bend in dna

Question 46

How are mutations avoided during replication?

Answer 46

DNA polymerases proofread and repair errors

Question 47

How are mutations fixed after replication occurs?

Answer 47

mismatch repair, enzymes identify mismatch, remove it and polymerase replaces it, ligase repairs and joins it to rest of strand

Question 48

What are glycosylases?

Answer 48

scan for and recognize specific base alterations

Question 49

What are nucleases?

Answer 49

cut the DNA on either side of the error

Question 50

How do repair enzymes know which DNA strand should be cut after replication?

Answer 50

original template strand is methylated and has methyl groups attached new one doesn't yet

Question 51

What are checkpoints in cell cycle? Why do we have them?

Answer 51

where it is checked that everything occurred properly and nothing is damaged do not want to pass on incorrect DNA to daughter cells