EEB 121 Week 1: Transcription/Translation Review, RNA, DNA

Question 1

Where does transcription occur in the cell in eukaryotes?

Answer 1

In the nucleus exclusively

Question 2

What is transcription?

Answer 2

Transcription is the process by which the information in a strand of DNA is copied into a new molecule of messenger RNA (mRNA)

Question 3

Briefly describe the steps involved in Transcription.

Answer 3

Transcription is carried out by RNA Polymerase and a number of proteins called transcription factors

Transcription factors bind to specific DNA sequences in order to recruit RNA Polymerase to an appropriate transcription site

Together they form a complex called the transcription initiation complex

This complex initiates transcription and RNA Polymerase begins mRNA synthesis

The mRNA molecule is elongated and, once the strand is completely synthesized, transcription is terminated

Question 4

List 3 RNA processing steps.

Answer 4

1. Addition of a 5’ (7-Methyl Guanosine) cap
2. Polyadenylation: addition of a Poly-A tail at the 3’ end
3. RNA splicing to remove introns

Question 5

Where does translation occur in the cell in eukaryotes?

Answer 5

In the cytoplasm

Question 6

What is translation?

Answer 6

Translation is the process of synthesizing polypeptide chains (from mRNA templates) assembling them into the correct amino acids to form proteins

(Basically, the process of generating proteins from RNA)

Question 7

Describe the role of Aminoacyl tRNA (transfer RNA) in translation.

Answer 7

Facilitates base pairing carrying amino acids to the ribosomes during protein synthesis to form a polypeptide chain

Question 8

Describe the role of Aminoacyl tRNA Synthetase in translation.

Answer 8

Catalyzes the formation of “charged” tRNA

Question 9

Describe the role of Ribosome in translation.

Answer 9

Site of translation made of large and small subunits when mRNA binds (and protein synthesis occurs)

Question 10

What is the ribosome composed of?

Answer 10

Ribosomes consist of two major components: (1) the small ribosomal subunit, which reads the RNA, and (2) the large subunit, which joins amino acids to form a polypeptide chain

(Complexes of rRNA molecules and proteins, large subunit+small subunit)

Question 11

Name and describe the 3 binding sites for tRNA.

Answer 11

1. The A site (acceptor site), binds to the aminoacyl tRNA, which holds the new amino acid to be added to the polypeptide chain
2. The P site (called the peptidyl site), binds to the tRNA holding the growing polypeptide chain of amino acids
3. The E site (exit site), serves as a threshold, the final transitory step before a tRNA disposes of its amino acid

Question 12

Building a polypeptide is a complex process with multiple steps. Describe 4 steps that are involved in building a polypeptide

Answer 12

Codon recognition at A Site
Peptide bond formation
Translocation: Exit
Termination: Recognition of Stop Codon

Question 13

How is RNA different from DNA?

Answer 13

1. RNA is single stranded, can fold back on itself , and act as an enzyme
2. RNA has uracil instead of thymine ( exception tRNA has thymine)
3. RNA is less stable → OH group makes RNA more prone to nucleophilic attack
4. Ribose in RNA and deoxyribose in DNA

Question 14

Why isn’t RNA still the primary information molecule of life?

Answer 14

RNA isn’t that stable and it is not the best catalyst

Question 15

Transition between RNA to DNA.

1. What process do the arrows represent?
2. Which alteration is the most common?
3. Why might these spontaneous chemical alterations be significant?

Answer 15

1. Vertical→ Methylation
   Horizontal → Deamination
2. The deamination of cytosine to uracil is the most common base alteration
3. This may explain why RNA needed to exist before DNA; explaining the RNA World

Question 16

Mutations (variation) affect the ________ while selection acts on the ________.

Answer 16

Mutations (variation) affect the genotype while selection acts on the phenotype