DNA Replication

Question 1

Origin Site

Answer 1

The origin of a replication bubble

Question 2

Helicase

Answer 2

Unwinds the helix structure to allow access to the parent strand for replication

Question 3

Single Strand Binding Proteins

Answer 3

Temporarily bind to the unwound template strands to keep them open for replication

Question 4

Topoisomerase

Answer 4

Stabilizes the overtwist ahead of helicase

Question 5

Primase

Answer 5

Lays down RNA primers at the beginning of Okazaki fragments (and one at the beginning of the leading strand) as a signal for poly III to start building there

Question 6

DNA Polymerase III

Answer 6

• Reads the parent strand from 3 to 5
• Builds a new daughter strand from 5 to 3
• Cannot initiate synthesis on its own, so it relies on an RNA primer to tell it where to start

Question 7

DNA Polymerase I

Answer 7

Replaces the RNA primers with the proper nucleotides

Question 8

Ligase

Answer 8

Glues Okazaki fragments together

Question 9

DNA Polymerase II

Answer 9

• Rereads the strand once it has been replicated and fixes any mistakes

Question 10

Telomeres

Answer 10

• DNA strands get shorter every time they are replicated. This is because the last RNA primer is taken off the end of the strand, but Polymerase is unable to replace it since there is no 3’ end with a primer to kickstart it. This means the last few nucleotides on the end of the strand stay unpaired and are later removed because they are not useful
• Telomeres are long nucleotide sequences on the ends of DNA strands that do not code for anything. They help postpone the erosion of useful DNA

Question 11

Telomerase

Answer 11

Catalyzes the lengthening of telomeres in germ cells

Question 12

3 Stages of mRNA and Protein Synthesis

Answer 12

• Transcription
• RNA processing
• Translation

Question 13

Transcription

Answer 13

• Catalyzed by RNA polymerase
• Builds strings of mRNA based off a DNA template strand
• Follows base pairing rules with thymine substituted for uracil
• 3 stages

Question 14

Transcription Initiation

Answer 14

• Promoters signal for the initiation of RNA synthesis
• Transcription factors sense this signal and bind to the promoter site to help guide the RNA polymerase
• RNA polymerase attaches to the promotor site / transcription factors
• Promotors are long strands of adenine and thymine called the TATA box

Question 15

Transcription Elongation

Answer 15

• RNA polymerase moves along the DNA strand
• It untwists the double helix, exposing 10-20 base pairs at a time
• Base pairs the DNA template strand with RNA nucleotides, which then fall away to create their own single pre mRNA strand

Question 16

Transcription Termination

Answer 16

• After each stop codon is a poly-A sequence
• Proteins cut the mRNA free 10-35 nucleotides past the poly-A
• Polymerase falls away from the DNA strand
• This process is not well understood

Question 17

RNA Processing

Answer 17

• 5’ end receives a modified nucleotide cap
• 3’ end gats a poly-A tail
• RNA splicing occurs, which cuts out introns and join together exons

Question 18

Introns

Answer 18

Segments of RNA that do not code for any amino acids

Question 19

Exons

Answer 19

Segments of RNA that code for amino acids

Question 20

Spliceosomes

Answer 20

• snRNP (small nuclear ribonucleoproteins)
• These recognize splice sites and do the intron cutting

Question 21

Translation

Answer 21

• Formation of a protein using mRNA strands as a template

Question 22

Anti-codon

Answer 22

• Base pairs on the tRNA that bind with those on the mRNA strand

Question 23

Aminoacyl-tRNA Synthetase

Answer 23

Binds amino acids to the correct tRNA strand

Question 24

Binding sites on the Ribosome

Answer 24

• Add site - reads mRNA and calls in the matching tRNA
• Peptide site - adds on the amino acids
• Exit site

Question 25

Translation Initiation

Answer 25

New mRNA is brought into the ribosome, as well as the first amino acid which matches with the start codon (Met)

Question 26

Translation Elongation

Answer 26

Amino acids are added to the polypeptide

Question 27

Translation Termination

Answer 27

• Ribosome reaches the mRNA’s stop codon
• It accepts the release protein
• Hydrolysis and release occur

Question 28

Polyribosome

Answer 28

Many ribosomes translating a single mRNA strand at once

Question 29

Post-translation Changes

Answer 29

• Some proteins may harm the cell if they are left in their regular state post-translation, like insulin when the cell is not ready for it
• In order to counter this, the cell changes the protein reversibly until it is ready to use it

Question 30

Epigenetics

Answer 30

• Chemical messengers determine whether a certain gene is expressed
• Methylation suppresses small segments of genes
• Histones control longer portions