2.3 - Replication, Transcription, Translation

Question 1

What is transcription?

Answer 1

The transfer of information from a DNA molecule to an RNA molecule; the construction of an mRNA molecule based on the sequence of bases in a section of a DNA molecule

• Turning DNA into a message using RNA (this occurs in the nucleus)

Question 2

What is translation

Answer 2

The transfer of information from an RNA molecule to a polypeptide; the construction of a new polypeptide based on the sequence of bases in a mRNA molecule

• Protein synthesis (accomplished in a ribosome)

Question 3

What is RNA polymerase?

Answer 3

The enzyme that performs transcription; it forms a polymer of RNA from free RNA nucleotides

Question 4

What is a ribosome?

Answer 4

The site (organelle) in a cells where translation occurs

Question 5

What is tRNA?

Answer 5

The intermediary between mRNA coded information and the amino acid building blocks of proteins.

• Transfer RNA = carries an amino acid for later protein synthesis

Question 6

What is DNA replication?

Answer 6

DNA replication is when we make an identical copy of our gene recipe book

• Occurs during synthesis
  ** Exact copy of all As, Gs, Ts, and Cs

Question 7

What is our greatest concern when making protein during DNA replication?

Answer 7

We want to keep our protein recipe book/instructions accurate and complete when we decide to divide our cells (mitosis) or make gametes (meiosis)

Question 8

What occurs during DNA replcation?

Answer 8

DNA unzips and copies itself when genes need to be copied (Eg. Gametes). Starts at special sites – “origins of replication”. DNA replication goes in both directions away from origin site.

Question 9

What enzyme is responsible for the “unzipping” of DNA?

Answer 9

DNA unzips because of helicase (think helix-ase = unwinding the double helix of DNA)

Question 10

What enzyme is responsible for the replication of DNA?

Answer 10

DNA replicates because of DNA polymerase (think polymer-ase = building a new polymer/strand of DNA)

Question 11

What enzyme is responsible for identifying the ‘starting point’ for DNA replication?

Answer 11

DNA replication begins at a primer which is created by primase (think primer-ase = making a primer/starting point)

• Primer is made of RNA nucleotides (U, A, G, C)

Question 12

What enzyme is responsible for gluing DNA fragments together?

Answer 12

DNA fragments are glued together by ligase (there is no cutesy short form for this one lol)

• Gaps in new DNA strand are glued together with ligase

Question 13

What is it called when DNA is pulled apart?

Answer 13

When DNA is pulled apart, it is called a replication bubble or an origin of replication

Question 14

What does semi-conservative mean?

Answer 14

Semi-conservating means there is 1 parent strand (the original strand of DNA) and one new strand (the copied version of DNA)

Question 15

T/F: Mistakes during the initial paring of template and completementary nucleotides are very common

Answer 15

False: Enzymes proofread DNA during replication and repair damage in existing DNA; errors occur at a rate of 1 in 10,000 base pairs

Question 16

What happens if there is an incorrect pairing during DNA replication?

Answer 16

If there is an incorrect pairing, the enzyme removes the wrong nucleotide and then resumes synthesis.

Question 17

What is the final error rate of DNA replication (after initial pairing phase)?

Answer 17

The final error rate is only one per billion nucleotides.

Question 18

What are the 3 stages of transcription?

Answer 18

1. Initiation
2. Elongation
3. Termination

Question 19

What occurs during initiation?

Answer 19

• RNA Polymerase binds to a promoter/start point
• DNA unwinds
• RNA synthesis begins
• Promoter tells the polymerase to “sit down” and begin transcribing RNA

Question 20

What occurs during elongation?

Answer 20

• Polymerase moves downstream
• DNA helix reforms
• RNA strand gets longer thanks to the addition of new/ complementary nucleotides (copies template strand)

** Keeps going until a termination sequence is reached

Question 21

What occurs during termination?

Answer 21

• RNA transcript is released
• Polymerase detaches
• Termination signal tells polymerase to stop building

** 5’ cap and Poly(A) tail (aglets) put on the ends to protect recipe from degradation

Question 22

What occurs during translation?

Answer 22

1. mRNA joins with small ribosomal subunit
2. tRNA “base pairs” with mRNA appropriate 3 bases (start code is always AUG - methonine)
3. Large ribosomal subunit joins
4. Elongation (codon recognition, peptide bonds form, tRNa translocates to the next codon down)
5. Translation ends when a termination sequence is reached (UAA, UAG, UGA = stop)*

• Newly made protein is released

Question 23

What is a codon?

Answer 23

A codon is a combination of 3 RNA nucleotides (A, C, G, U) used to code for amino acids

Question 24

What is the codon dictionary?

Answer 24

The codon dictionary is a dictionary containing all the possible codon “words” (64 possible)

Question 25

What do coden sentences start/end with?

Answer 25

• All sentences start with AUG (methanine)
• All sentences end at a “stop” codon (UAA, UAG, UGA)

Question 26

What are the various forms of mutation?

Answer 26

• Silent mutation
• Missence mutation
• Frameshift mutation
• Nonsense mutation

Question 27

What does silent mutation mean?

Answer 27

Silent mutation means your recipe book is screwed up and your letters have changed, but they code for the same amino acid, so everything is fine (you have no visible mutations)

Question 28

What does missence mutation mean?

Answer 28

Missence mutation means your recipe book is screwed up and a single amino acid in the chain is the wrong one (most of the time, you die/aren’t even born; if you live, you have diseases/disorders)

• Cystic fibrosis, Sickle Cell, etc.

Question 29

What does frameshift mutation mean?

Answer 29

Frameshift mutation means you have too many/too few nucleotideds in an amino acid, so the order is wrong for the rest of the line, resulting in ALL NEW amino acids from that point on (AUG-AGG-UG- see how this is bad?)

• ALS, Muscular Dystrophy, etc.

Question 30

What does nonsense mutation mean?

Answer 30

Nonsense mutation means you have a premature stop codon, and the sequence stops too early

• PKU, BRCA1 breast cancer gene, etc.