DNA transcription, replication and translation

Question 1

What are two similarities in the structure of DNA and RNA?

Answer 1

Phosphates always attached to 5’ and 3’ carbon of each sugar

Nitrogenous bases always attached to 1’ carbon of each sugar

bases = purine or pyrimidine

Question 2

Where is the Nitrogenous bases always attached to?

Answer 2

1’ carbon of each sugar

Question 3

Describe the structure of purines vs pyrimidines.

Answer 3

Purine = double ring structure

Pyrimidine = single ring structure

Question 4

In which direction can polynucleotides of DNA and RNA only be synthesised?

Answer 4

Polynucleotides

Question 5

Where are additional nucleotides added in RNA and DNA?

Answer 5

3’ end

Question 6

What enzyme adds the precursor (nucleotide triphosphate) to DNA and RNA?

Answer 6

polymerase

Question 7

Transcription

Answer 7

When the code of DNA is temporarily transferred to RNA (Copying of DNA –> RNA)

Question 8

What enzyme is responsible for unwinding and separating DNA in replication

Answer 8

Helicase

Question 9

What enzyme is responsible for reading strand template and inserting complementary bases in replication

Answer 9

polymerase

Question 10

How is the leading strand of DNA produced?

Answer 10

continuously due to the polarity of 5’-3’

Question 11

How is the lagging strand of DNA produced?

Answer 11

discontinuously replicated. Therefore is synthesized as Okazaki fragments

Question 12

What enzyme seals the gap between Okazaki fragments?

Answer 12

DNA Ligase

Question 13

What is the role of RNA Polymerase?

Answer 13

Required to make RNA from free nucleoside triphospates

moves along DNA from 3’ end to 5’ end inserting complementary bases

Question 14

What are the three steps of transcription? Explain

Answer 14

Initiation – RNA polymerase moves to precursor and starts to unwind DNA

Elongation – RNA polymerase reads DNA (3’-5’) and produces RNA transcript adding nucleotides in a (5’-3’) direction.

Termination – RNA polymerase reaches termination site, RNA transcpit set free and polymerase dissociates

Question 15

What is an example of gene regulation?

Answer 15

TATA box: DNA sequence where genetic sequence can be rad and decoded = promoter sequence that specifies where transcription begins.

Question 16

What occurs in the transcription initiation step and act as important control.

Answer 16

Transcription factors
promoter sequences
regulatory sequences
enhancer sequence

Question 17

What are the non coding regions of eukaryotic DNA and how are they removed?

Answer 17

Introns

via mRNA splicing

Question 18

What are the seven regions of Eukaryotic DNA?

Answer 18

Gap

2- 5’-non coding region

3- start codon (AUG)

4- Coding region/ open reading frame

5- Stop codon (UGA)

6- 3’ non coding region

7- ply A tail

Question 19

What is the code for start codon?

Answer 19

AUG

Question 20

What is the code for end codon?

Answer 20

UGA

Question 21

What are the five steps in mRNA Processing?

Answer 21

1- 5’ capped with modified Guanine reside

2- 3’ polyadenylated (add strong of A)

3- Poly A tail of mRNA generated

4- spliced

5- transported to cytoplasm

Question 22

Outline main differences in prokaryotic and eukaryotic DNA.

Answer 22

Prokarotic are coded in a continous blcok where as Eukaryotic have exons (coding) and introns (non coding)

E undergoes mRNA processing (cap, tail) and mRNA slicing but P does not

Question 23

General overview of translation

Answer 23

After mRNA is exported from nucleus it becomes bound to a ribosome which reads mRNA and uses tRNA to assemble a polypeptide.

Amino acids selected, collected and carried to ribosome by tRNA

TRNA enters ribosome and mind to mRNA chain

Question 24

What three steps are used in both transcription and translation?

Answer 24

Initiation
Elongation
Termination

Question 25

What are the 4 steps of translation elongation?

Answer 25

Codon recognition (incoming tRNA anticodon pairs with mRNA codon)

Peptide bond formation- ribosome catalyses bond formation between amino acids

Translocation- tRNA leaves P site of ribosome, ribsome moves down mRNA 3 bases

Repeat as required

Question 26

What occurs in translation elongation?

Answer 26

Reaches stop codon which does not bind to any anticodons of tRNA

Release factor binds to stop codon to promote hydrolysis of peptide bond between polypeptide and tRNA at P site.

Question 27

What are the different types of point mutations?

Answer 27

Silent, nonsense and missense

Question 28

Describe silent mutations

Answer 28

base change but codon does not alter AA sequence

Question 29

Describe nonsense point mutations

Answer 29

Base change creates a stop codon

translation ends prematurely = mutant protein

Question 30

Describe missense point mutation. Define Conservative and non-conservative ones.

Answer 30

base change resulting in new AA

C= properties of new AA similar = normal protein function

NC= new AA different properties = loss of protein function

Question 31

What is a frameshift mutation?

Answer 31

Insertion / deletion of base that alters sequence of codon