Topic 15 - Ribosomes and Protein Synthesis

Question 1

Gene

Answer 1

Region of DNA that contains a code that specify proteins through RNA

Question 2

Central Dogma of Gene Expression

Answer 2

Genes specify the sequence of mRNAs, which in turn specify the sequence of proteins

Question 3

Codon

Answer 3

Three consecutive nucleotides in mRNA that specify the insertion of an amino acid or the release of a polypeptide chain during translation

Question 4

Anticodon

Answer 4

Three-nucleotide sequence in a tRNA molecule that corresponds to an mRNA codon

Question 5

What does “the genetic code is redundant but specific” mean?

Answer 5

• Redundant: more than one codon corresponds with each amino acid
• Specific: a codon specifies only one amino acid

Question 6

What are the 3 kinds of RNA involved in protein synthesis? Describe what each does.

Answer 6

1. mRNA (messenger RNA)
   - carries the coding sequences for protein synthesis (transcripts)
2. tRNA (transfer RNA)
   - carries amino acids to the ribosomes during protein synthesis; does translation
3. rRNA (ribosomal RNA)
   - forms the core of a cell’s ribosomes (the structures in which protein synthesis takes place)

Question 7

Where does transcription take place?

Answer 7

Nucleus

Question 8

What is the final product of transcription?

Answer 8

mRNA strand

Question 9

What enzyme adds RNA nucleotides to create mRNA?

Answer 9

RNA polymerase

Question 10

Which RNA nucleotides are complementary to the DNA nucleotides adenine, thymine, guanine, and cytosine?

Answer 10

Uracil, adenine, cytosine, and guanine

Question 11

What do transcription factors do? What are they made of? What is the transcription initiation complex?

Answer 11

Transcription factors are proteins involved in the process of converting, or transcribing, DNA into RNA. Transcription factors include a wide number of proteins, excluding RNA polymerase, that initiate and regulate the transcription of genes.

Question 12

Which strand is transcribed to make mRNA - the coding strand or the template strand?

Answer 12

Template strand

Question 13

What happens during eukaryotic pre-mRNA processing?

Answer 13

• When an RNA transcript is first made in a eukaryotic cell, it is consider a pre-mRNA and must be processed into mRNA
• A 5’ cap is added to the beginning of the RNA transcript and a 3’ poly-A tail is added to the end
• Introns (“junk” sequences) are removed and exons are put back together by spliceosomes

Question 14

Where does transcription take place?

Answer 14

Ribosomes

Question 15

What is the final product of translation?

Answer 15

Polypeptide chain (protein)

Question 16

What happens on the small and large ribosomal subunits?

Answer 16

The small subunit decodes the genetic message and the large subunit catalyzes peptide bond formation.
- mRNA is “fed” through the ribosome; tRNA goes through the A, P, and E sites in the large subunit

Question 17

Where are codons found?

Answer 17

mRNA

Question 18

Where are anticodons found?

Answer 18

tRNA

Question 19

What is the relationship between a codon and an anticodon?

Answer 19

Codons in the mRNA bind to the anticodons in the tRNA during protein synthesis (translation)

Question 20

Aminoacyl-tRNA synthetase

Answer 20

Enzyme that attaches the appropriate amino acid onto its corresponding tRNA (first step of translation)

Question 21

Initiation

Answer 21

Ribosome assembles around the target mRNA (forming an initiation complex) and the start codon 5’ AUG is recognized

Question 22

Elongation

Answer 22

The tRNA transfers an amino acid to the tRNA bound to the next codon, forming a peptide bond between the two amino acids. The ribosome then shifts to the next codon to continue the process, creating a polypeptide chain.
- tRNA moves through the A, P, and E sites of the ribosome respectively.

Question 23

Termination

Answer 23

Elongation continues until a “stop” codon enters the A site on the ribosome, terminating the process.

Question 24

Point mutation

Answer 24

Occurs when a single base-pair is added, deleted or changed

Question 25

What is a mutagen? Give some examples.

Answer 25

Any chemical or physical agent that causes a mutation, such as carcinogens or radiation

Question 26

Why do base insertions or deletions tend to have a larger effect than base substitutions?

Answer 26

Frame-shift mutations are insertions or deletions of nucleotide bases in numbers that are not multiples of three, i.e. larger mutations; this in turn completely alters the entire protein sequence that occurs after the mutation

Question 27

What are the types of chromosomal mutations?

Answer 27

Deletion
- Part of chromosome is removed
Duplication
- Part of chromosome is copied
Inversion
- Part of chromosome is flipped
Translocation
- Part of chromosome is moved to a new location

Question 28

How does genetic variation arise?

Answer 28

Meiosis, sexual reproduction, mutations

Question 29

Evolution

Answer 29

The change in the characteristics of a species over time via the process of natural selection

Question 30

Natural selection

Answer 30

The process whereby organisms better adapted to their environment tend to survive and produce more offspring