Molecular biology : replication,transcription & translation

Question 1

How is DNA an amphipathic molecule?

Answer 1

Sugar-phosphate backbone hydrophilic and water soluble.

The nitrogenous bases are hydrophobic.

Question 2

What is the direction/polarity of the parent strand in DNA replication?

Answer 2

3’ to 5’

Question 3

What is the only direction transcription and replication takes place in?

Answer 3

5’ to 3’

Question 4

Explain the steps of DNA replication.

Answer 4

1. The DNA strand will first separate from each other and forma structure called the replication fork.
2. Enzymes will use each strand as a template for the assembly of new nucleotides for the complementary strand.
3. Dna polymerase will continously synthesize one of the DNA strand. the other strand will be synthesized in pieces and these pieces will be joined together by DNA ligase.

Question 5

What type of model does DNA replication follow and why?

Answer 5

DNA replication follows a semiconservative model, because half of the parent DNA helix is conserved into each daughter molecule.

Each new DNA helix has one old strand with one new strand.

Question 6

What is the difference between 5’ end and 3’ end?

Answer 6

5’ end has a carbon attached to a phosphate group

3’ end has a carbon attached to a hydroxyl group

Question 7

Differentiate between transcription and translation?

Answer 7

1. Transcription is the synthesis of RNA under the direction of DNA.
2. Occurs in the nucleus
3. Translation is the synthesis of proteins under the direction of RNA.
4. Occurs in the cytoplasm

Question 8

What are the steps of transcription?

Answer 8

1. Initiation : The DNA unzips and the RNA nucleotides line up , followed by the RNA polymerase binding to the promotor.
2. Elongation : The RNA polymerase keeps adding nucleotides and therby the newly formed RNA strand grows.
3. Termination : RNA polymerase will keep adding nucleotides until it reaches a specific sequence of DNA called the terminator.This signals the RNA polymerase to detach from the DNA strand and also detaches the newly formed RNA.

Question 9

What is the promoter in transcription?

Answer 9

The promoter is a sequence of nucleotides that is responsible for determining when the transcription process begins.

Question 10

What is the terminator in transcription?

Answer 10

The terminator is a specific sequence of nucleotides that signals the end of the transcription process.

Question 11

Why is the process of splicing ,capping and tailing necessary?

Answer 11

The newly formed RNA strand is not readily usable for translation. It needs to undergo splicing to transform into a mRNA.

Capping/ tailing is to signal the cytoplasm that the mRNA is not foreign. If the cyctoplasm thinks an mRNA is foreign it will be digested by enzymes.

An mRNA conveys genetic messages from the DNA to the translation process.

Question 12

What is splicing, capping and tailing?

Answer 12

Splicing is the process in which the introns
( uncoded parts of RNA) get spliced off and the exons (expressed parts of a gene) get spliced together.

A cap and a tail is also added.

Question 13

What is the code for RNA nucleotides to become 1 amino acid?

Answer 13

3 RNA nucleotides = 1 amino acid
(A codon)

Question 14

Name the start and stop codons.

Answer 14

Start codon : AUG (codes for methionine)
Stop codons : UAG, UGA, UAA

Question 15

Name the types of RNA and their functions.

Answer 15

mRNA (messanger RNA) : Coding RNA used as code to make protein

tRNA (transfer RNA) : Structural RNA that carries amino acids to the ribosome during translation

rRNA( ribosomal RNA) : Structural RNA that makes up subunits of ribosome

Question 16

What is the first step of translation?

Answer 16

1. Initiation : The mRNA will bind to the small subunit of the ribosome. The initiator tRNA will bind to the start codon and carries methionine. Then the anticodon pairs with the start codon. A large subunit of the ribsome binds to create a functional ribosome.

Question 17

What is the second step of translation?

Answer 17

As the mRNA moves one codon at a time relative to the ribosome, a tRNA with a complementary anticodon pairs with each codon in the A site

The growing polypeptide detaches from the tRNA in the P site and attaches to the amino acid in the A site via peptide bond

tRNA in the P site leaves, and the ribosome moves (translocates) the tRNA attached to the polypeptide from the A site to the P site

Question 18

What is the last step of translation?

Answer 18

Termination : Elongation continues until a stop codon reaches the ribosome’s A site.

Question 19

What is mutation ? How is it caused?

Answer 19

Mutations are changes in the genetic information of a cell, caused by either:

1. errors in DNA replication/recombination
2. physical or chemical agents called mutagens.