Chapter Three: Protein Synthesis and Mutations

Question 1

The Genetic Code

Answer 1

A set of rules for determining how genetic information in the form of a nucleotide sequence is converted to an amino acid sequence.

Question 2

The Triplet Hypothesis

Answer 2

The genetic code consists of a combination of three nucleotides called a codon.

Question 3

Three Important Characteristics of the Genetic Code

Answer 3

1. Redundant: more than one codon can code for the same amino acid
2. Continuous: the code is read as a series of three-letter codons
3. Universal: all organisms build proteins with the same genetic code

Question 4

General Amino Acid Structure (4)

Answer 4

1. Central carbon
2. Amino Group
3. Side chain: identifies specific amino acid
4. Carboxyl group

Question 5

Gene Expression: Transcription

Answer 5

A DNA sequence serves as a template for the synthesis of RNA (exact copy)

Question 6

Types of RNA (3)

Answer 6

1. Messenger RNA (mRNA): the template for translation; transcripted from DNA then binds to ribosome during translation
2. Transfer RNA (tRNA): Brings the amino acids and anticodons to the ribosome for translation
3. Ribosomal RNA (rRNA): makes up the ribosome

Question 7

Gene Expression: Translation

Answer 7

An mRNA sequence serves as a template for the synthesis of a protein

Question 8

Transcription: Initiation

Answer 8

• transcription machinery assembled
• template strand (3’ to 5’) is transcribed
• RNA polymerase binds to the promoter region on the DNA and unwinds the correct section of the double helix

Question 9

Transcription: Elongation

Answer 9

-RNA polymerase moves in the 5’ to 3’ direction to create a complimentary strand

Question 10

Transcription: Termination

Answer 10

-specific nucleotide sequences in the DNA template signal the polymerase to stop
the new mRNA strand is released and the DNA helix reforms

Question 11

Ribosomes

Answer 11

• Composed of tRNA and proteins

- Comprised of two sub-units: small and large. Three binding sites for tRNA and one for mRNA

Question 12

Translation factors

Answer 12

Proteins that act as accessory factors; needed at every phase of translation

Question 13

Functional Regions of tRNA (2)

Answer 13

1. The anticodon loop; sequence of three nucleotides that is complimentary to an mRNA codon
2. The acceptor stem; a single stranded region where an amino acid is attatched

Question 14

Aminoacyl-tRNA Synthentase

Answer 14

Enzyme which attaches the correct amino acid sequence to a tRNA

Question 15

Translation: Initiation

Answer 15

• translation factors, mRNA, tRNA, and ribosomes assemble
• mRNA and tRNA bind to the ribosome
• the start codon sets the reading frame, which established how the codons will be read

Question 16

Binding sites for tRNA (3)

Answer 16

1. Amino/Acceptor site (A): holds the tRNA wth the next amino acid
2. Peptide site (P): contains the tRNA that carries the growing polypeptide
3. Exit site (E): holds the tRNA that has released its amino acid

Question 17

Translation: Elongation

Answer 17

• one amino acid is added at a time to the growing peptide chain
• elongation factors facilitate growth, amino acids are joined by peptide bonds

Question 18

Translation: Termination

Answer 18

• stop codon is reached, the polypeptide separates from the translation machinery
• poplypeptide is cleaved and released to carry out it’s function as a protein

Question 19

Single-Gene Mutation

Answer 19

Changes to the nucleotide sequence of one gene. Can be categorized according to 1, how they affect the nucleotide sequence of DNA, or 2, how they affect the amino acid sequence of a protein

Question 20

Point mutation (3)

Answer 20

Change in a single base pair of a DNA sequence

-substitution, addition, or deletion

Question 21

Frameshift Mutation

Answer 21

The insertion or deletion of nucleotides not divisible by three. Changes the reading frame

Question 22

Silent mutation

Answer 22

Does not change the amino acid sequence of a protein due to the redundancy principle

Question 23

Missense Mutation

Answer 23

Changes the amino acid sequence and are usually harmful

Question 24

Nonsense Mutation

Answer 24

Introduce an early stop codon to the reading frame. Usually harmful.

Question 25

Chromosome Mutation (4)

Answer 25

Mutation that changes in chromosomes or genes

-deletion, duplication, inversion, translocation

Question 26

Causes of a Spontaneous Mutation (3)

Answer 26

• normal molecular interactions
• incorrect base pairing
• transposition; a transposon moves within and between chromosomes

Question 27

Causes of an Induced Mutation

Answer 27

• Physical mutagens: distorts the physical structure of the DNA (X rays, UV rays)
• Chemical mutagens: molecules that enter the nucleus of a cell and chemically reacts with DNA (nitrites, chemicals in cigarette smoke)

Question 28

RNA Polymerase

Answer 28

Group of Enzymes that catalyze the synthesis of RNA. Do not require a primer like DNA polymerase