Steps for DNA Replication, RNA & Protein Synthesis

Question 1

What are the steps for DNA replication?

Answer 1

1) DNA replication usually proceeds bidirectionally (anti-parallel)
2) Helicase Enzyme separates the two DNA strands and unwinds into single strands
3) The junction between the unwound part and the open part is called a replication fork
4) Topoisomerase (DNA Gyrase), creates a nick ahead of the replication fork to reduce the torsional strain and supercoiling
5) SSBPs (Single Stranded DNA Binding Proteins) stabilizes the isolated strands to prevent them from snapping back together
6) DNA replication requires a RNA primer to begin
7) Enzymes called Primase adds a PRIMER to the starting point so that DNA replication can begin
8) DNA Polymerase is now able to add nucleotide and continue the DNA replication
9) DNA Polymerase III adds nucleotides in the 5’ to 3’ direction (elongates the leading and lagging strand)
10) Due to lagging strand, DNA replication is discontinuous
11) DNA Polymerase I removes RNA primer on lagging strand and replaces it with DNA bases
12) Multiple fragments of newly synthesized DNA will be generated (Okazaki Fragments)
13) DNA Ligase seals the gap between the Okazaki Fragments (joins together) after primer is replaced with DNA

Question 2

What are the important players in DNA replication? (7)

Answer 2

1) DNA Helicase
2) Topoisomerase
3) Single Stranded DNA Binding Proteins
4) Primase
5) DNA Polymerase III
6) DNA Polymerase I
7) DNA Ligase

Question 3

During replication, there will be multiple replication forks.
What will it cause and how can we prevent it? (1 cause, 2 preventions)

Answer 3

It will cause replication errors and may cause a genetic mutation.

To prevent this:
1) proofreading is done by the polymerase to prevent mismatches
2) damaged DNA can be repaired by the DNA repair enzymes

Question 4

How are proteins synthesized from the DNA? (4)

Answer 4

1) DNA is transcribed into mRNA (messenger RNA)
2) mRNA leaves the nucleus and travels to the cytoplasm
3) The mRNA sequence is then translated into amino acids in the ribosomes
4) Amino acids form a peptide chain - a protein

This process is also sometimes referred to as “The Central Dogma”

Question 5

What are the main ingredients needed for (Transcription) mRNA synthesis? (5)

Answer 5

1) DNA Template
2) RNA Polymerase
3) rNTP’s
4) Transcription Factors
5) ATP

Question 6

What is the process for Transcription? (4)

Answer 6

1) Enzyme RNA polymerase binds tightly to a promoter (starting point)
2) RNA polymerase opens up the DNA helix
3) The enzyme adds new RNA nucleotides that are complementary to the template DNA
4) mRNA is made

*Promoter is a region of DNA with special nucleotide sequence that marks the beginning of a gene

Question 7

What is the mRNA processing steps? (3)

Answer 7

*Newly synthesized primary mRNA must be processed before it can be used properly

1) Capping (Addition of a 7 methyl-guanosine, 7mG cap)
2) Addition of poly-A sequences
3) Splicing (Removal of introns and rejoins of exons)

*Processing is necessary as it stabilizes the mRNA
*After processing, it is mature mRNA

Question 8

What is the process for Translation? (9)

Answer 8

1) mRNA travels from nucleus to the cytoplasm to the ribosome
2) Amino acids exist freely in cytoplasm
3) Each 3 bases (codon) translates to a single amino acid
4) The ribosome looks for the “start” codon - AUG, and this is where the chain begins
5) Transfer RNA (tRNA), has an anticodon at one end and an amino acid at the other, it binds to a complementary codon
6) Another tRNA reads the next codon and the amino acid attached to it binds with the amino acid on the previous tRNA using a peptide bond. The first tRNA falls off
7) This process continues until the “stop” codon is reached
8) A protein called release factor binds to the “stop” codon and cleaves the polypeptide from the last tRNA
9) The amino acid chain folds into a 3 dimensional structure, now a protein.
10) The protein can be an enzyme, a hormone

Question 9

What are the main ingredients needed for Translation? (7)

Answer 9

1) mRNA
2) Transfer RNA (tRNA)
3) Ribosomes
4) Amino acids
5) Start codon, AUG
6) Stop codon, UAG/UAA/UGA
7) Release factors

Question 10

What are the steps for Translation? (3)

Answer 10

1) Initiation
2) Elongation
3) Termination

Question 11

What are involved in DNA replication? (4)
Hint: dEET

Answer 11

1) deoxyriboNucleosideTriPhosphate (dNTP)
2) Energy Source (ATP)
3) Enzyme & Proteins
4) Template DNA