Unit 5

Question 1

What is Chargaff’s rule?

Answer 1

The number of A=T and the number of G=C

Question 2

How many origins of replication can eukaryotes have?

Answer 2

hundreds or thousands

Question 3

What is the replication fork?

Answer 3

a Y-shaped region where parental DNA strands are unwound

Question 4

What are helicases?

Answer 4

enzyme that untwists the double helix at the replication fork

Question 5

What is topoisomerase?

Answer 5

an enzyme that relieves strain of the DNA untwisting

Question 6

What does DNA polymerase do?

Answer 6

makes new DNA at the replication fork?

Question 7

What is the difference between the leading and the lagging strand?

Answer 7

the leading strand is continuously built toward the replication fork, but the lagging strand works in small sections away from the replication form in pieces called Okazaki fragments

Question 8

What else does DNA polymerase do?

Answer 8

proofread newly made DNA

Question 9

What happens in mismatch repair?

Answer 9

repair enzymes replace incorrectly paired nucleotides

Question 10

What do telomeres do?

Answer 10

they postpone the erosion of genes near the ends of DNA molecules

Question 11

Where does transcription occur in a eukaryotic cell?

Answer 11

the nucleus

Question 12

Where does translation take place in a eukaryotic cell?

Answer 12

cytoplasm

Question 13

What is the first stage of gene expression?

Answer 13

transcription

Question 14

What is a promotor?

Answer 14

what initiates transcription

Question 15

What are transcription factors?

Answer 15

proteins that help control the rate of transcription by turning on and off genes

Question 16

What are the three stages of transcription?

Answer 16

initiation, elongation, termination

Question 17

What are introns?

Answer 17

noncoding segments

Question 18

What are exons?

Answer 18

a coding region of DNA that is eventually expressed

Question 19

How can a gene encode more than one kind of polypeptides?

Answer 19

by changing which segments are introns and exons (this is called RNA splicing)

Question 20

What does tRNA do?

Answer 20

It carries specific amino acids and the anticodonmust bind to the codons of the mRNA.

Question 21

How does accurate translation occur?

Answer 21

a correct match between a tRNA and an amino acid and a correct match between the tRNA anticodon and an mRNA codon

Question 23

What do free ribosomes synthesize?

Answer 23

proteins that function in the cytosol

Question 24

What do bound ribosomes do?

Answer 24

make proteins of the membrane system and proteins that are secreted from the cell

Question 25

Can ribosomes switch from free to bound?

Answer 25

yes because they are identical

Question 26

What is a polyribosome?

Answer 26

when multiple ribosomes can translate a single mRNA simultaneously so that multiple copies can be made at once

Question 27

What are the three types of nucleotide pair substitutions?

Answer 27

silent, missense, nonsense

Question 28

What is missense?

Answer 28

when a substitution causes the sequence to code for a different amino acid

Question 29

What is nonsense?

Answer 29

a substitution that leads to a stop codon

Question 30

What is a frameshift mutation?

Answer 30

when an insertion or deletion causes the reading frame to be altered

Question 31

What are mutagens?

Answer 31

physical or chemical agents that cause mutations

Question 32

What is an inducible operon?

Answer 32

an operon that is usually off until an inducer activates the repressor and turns on transcription (think about lactose example)

Question 33

When do inducible enzymes usually function?

Answer 33

catabolic pathways and they are induced by a chemical signal

Question 34

When do repressible enzymes usually function?

Answer 34

anabolic pathways and their production is repressed by a high level of the end product

Question 35

Why is gene expression regulation important?

Answer 35

almost all cells in an organism contain the same genes but not all the genes need to be on all the time

Question 36

Where is gene repression most often regulated?

Answer 36

translation

Question 37

What does histone acetylation do?

Answer 37

opens chromatin and regulates structure