DNA, Protein, and Central Dogma

Question 1

Define Transcription

Answer 1

To get from gene to protein, cell produces intermediate molecule called messenger RNA (mRNA)

Question 2

Define Translation

Answer 2

Cell uses mRNA to produce a protein

Question 3

Why does DNA have one direction

Answer 3

Because bases are only added from one end of the chain. Creates problems of a leading and lagging strand.

Question 4

Define DNA replication: Bacterial (1)

Answer 4

DNA has a specific start ‘origin’ of replication. Proceeds in both directions until the entire chromosome has been copied.

Question 5

Define DNA replication: Eukaryotic (1)

Answer 5

DNA has a specific start ‘origin’, and many simultaneous ‘replication bubbles’ expand in both directions and fuse as the copying of the daughter strand is completed.

Question 6

Define Helicase (2)

Answer 6

Untwists the DNA helix to give single-stranded DNA, increases coiling ahead of the replication fork.

Question 7

Define topoisomerase (2)

Answer 7

‘fixes’ the increased coiling in the DNA template. Transiently nicking both strands and allowing two strands to rotate around each other.

Question 8

Define single-stranded binding protein (2)

Answer 8

Stabilises the single-stranded template

Question 9

Define DNA Primase (2)

Answer 9

Synthesises RNA primer at 5’ end

Question 10

Define DNA Synthesis (3)

Answer 10

Uses nucleotide building blocks (ATP/TTP/CTP/GTP), and proceeds always in the 5’ to 3’ direction. Energy for polymerisation is supplied by incoming triphosphate nucleotide.

Question 11

Define DNA Polymerases (3)

Answer 11

Catalyse DNA synthesis

Question 12

Define leading/lagging strand (3)

Answer 12

DNA strands that are being replicated

Question 13

Define synthesis of leading strand (4)

Answer 13

1. DNA synthesis the enzyme DNA primase synthesises RNA primer
2. RNA primer is extended by DNA polymerase III
3. RNA primers removed by action of 5’ exonuclease activity of DNA polymerase I, DNA synthesised in their place at same time

Question 14

Define synthesis of lagging strand (4)

Answer 14

1. Basic mechanism of DNA synthesis is the same (5’-3’ direction)
2. New RNA primers have to be made frequently to keep DNA synthesis going.
3. Creates lots of DNA fragments (Okazaki) along the lagging strand.

Question 15

Define DNA polymerase I (4)

Answer 15

Removes RNA primers

Question 16

Define DNA ligase (4)

Answer 16

Okazaki fragments to create a continuous strand

Question 17

Define replication fork

Answer 17

Each replication fork produces new DNA. Depending on which direction the fork is moving in determines which strand is the leading or lagging strand.

Question 18

Define triplet codes

Answer 18

DNA sequence that encodes proteins.

Question 19

Define Codon

Answer 19

Group of three nucleotides in a row, most code for 1 amino acid. some encode a ‘start’ pr ‘stop’ signal for translation.

Question 20

What is the start codon

Answer 20

AUG

Question 21

Define frameshift mutation

Answer 21

If 1 letter is added or deleted, this changes every codon after the mutation and changes the reading frame.

Question 22

Define protein synthesis

Answer 22

Starts on free ribosomes in the cytoplasm. Proteins are trafficked to the ER if they’re gonna be membrane-bound, lysosomal, or secreted. Ribosomes stick to ER because of signal sequences on the protein chain.

Question 23

Define RNA translation

Answer 23

Translated immediately by packs of ribosomes that coat the RNA, stabilise it, and move it along it from 5’ to 3’ end. RNA coated with a cluster of ribosomes is called polyribosomes. Each ribosome makes the same protein, one after the other.

Question 24

How many common amino acids are there

Answer 24

20