Chapter 17.4-17.5 - Translation

Question 1

What is translation?

Answer 1

Mechanism by which the nucleotide sequence in an mRNA directs the synthesis of an amino acid polymer (polypeptide)

Question 2

tRNA (3)

Answer 2

• Carries amino acids and pairs with nucleotides (codons) in mRNA
• there are many different tRNAs in a cell
• each has a different anticodon sequence

Question 3

mRNA

Answer 3

mRNA codons specify amino acid sequences *look at diagrams in slides

Question 4

“Charging” tRNA (4)

Answer 4

1. Each tRNA carries a specific amino acid that corresponds to its anticodon
2. Aminoacyl- tRNA syntheses matches tRNA with specific amino acids
3. 20 different aminoacyl-tRNA synthetases (dunno if this is a word but it’s in my notes:p) (hey Sarah:p)

Question 5

Aminoacyl

Answer 5

tRNA synthase catalyzes the formation of a covalent bond between tRNA and amino acid

*DIAGRAM

Question 6

Ribosomes

Answer 6

Ribosomal RNA (rRNA) catalyzes formation of peptide bonds between amino acids

Question 7

Structure of ribosome (3 parts)

Answer 7

1. P site
2. A site
3. E site

Question 8

P site

Answer 8

Holds tRNA with attached peptide chain

Question 9

A site

Answer 9

Holds tRNA carrying amino acids to be added

Question 10

E site

Answer 10

From which discharged tRNA leaves ribosome

Question 11

3 repeating steps of Elongation

Answer 11

1. Codon recognition
2. Formation of peptide bond (polypeptide attached to tRNA site (A site))
3. Translocation P site (5’3’ on mRNA)

visuals on slide 11 in lecture 13

Question 12

Peptide Bond formation

Answer 12

Diagrams in notes and on slide 12 of lecture 13

Question 13

Translation Termination at Stop Codons (3)

Answer 13

1. Release factor breaks bond between polypeptide and tRNA
2. Structure distorts
3. Polypeptide releases

*diagram in slides

Question 14

Post-Translation Protein Modifications (3)

Answer 14

1. Folding of protein is determined by primary structure
2. Cleavage of polypeptide
3. Addition of chemical groups: sugars, phosphate etc.

Question 15

3 parts of Genetic Code:

Answer 15

• 3 nucleotides
• 1 codon
• 1 amino acid

*THE GENETIC CODE IS UNIVERSAL: a gene will be transcribed and translated into the same protein in all cells and organisms

Question 16

Genetic Code (2)

Answer 16

1. 1st codon AUG signals the start of translation

2. 3 codons are signals to stop translation

Question 17

The genetic code is: (2)

Answer 17

1. Redundant: several codons specify the same amino acid

2. Not Ambiguous: each codon specifies only one amino acid (related to quantity)

Question 18

Reading frame

Answer 18

LOOK AT NOTES FOR STEPS! Super important (think proteins l bio lab)

Question 19

Mutations (4)

Answer 19

1. Changes in nucleotide sequences (substitution, insertion, deletions etc) of DNA that lead to changes in amino acid sequence of protein (& RNA). This derives from spontaneous errors in DNA replication
2. If changes occur in reproductive cells they are passed on to offspring
3. Many mutations are detrimental in that they disrupt protein function and expression
4. Some mutations are silent

Question 20

Why are some mutations beneficial (2)

Answer 20

1. They can drive evolution

2. Confer a survival/reproductive advantage

Question 21

The three steps of Translation:

Answer 21

1. Initiation
2. Elongation
3. Termination