DNA, RNA and Protein Synthesis

Question 1

How is DNA stored in eukaryotic cells?

Answer 1

Linear DNA molecules that exist as chromosomes
DNA molecules are really long so has to be wound up so it can fit into the nucleus. It’s wound around proteins called histones.
These help to provide support

Question 2

How is DNA stored in prokaryotic cells?

Answer 2

Short and circular
Not wound around histones but it condenses to fit in the cell by coiling.

Question 3

What is messenger RNA (mRNA)?

Answer 3

Made during transcription. Carried genetic code from DNA to the ribosomes
Groups of three adjacent bases are usually called codons

Question 4

What is transfer RNA (tRNA)?

Answer 4

Involved in translation
Carries amino acids that are used to make proteins to the ribosomes
tRNA is a single polynucleotide strand thats folded into a clover shape
Hydrogen bonds between the specific base pairs hold it in this shape
Every tRNA molecule has a specific sequence of three bases at one end called an anticodon.
Has an amino acid binding site at the other end

Question 5

Explain transcription

Answer 5

RNA polymerase attaches to the DNA

Starts when RNA polymerase attaches to the DNA double helix at the start of a gene. In eukaryotes the hydrogen bonds between 2 DNA strands are broken by DNA helicase. This seperates the strands and uncoils it. One of the strands is then used to as a template to make an mRNA copy

Complimentary mRNA is formed

The RNA polymerase lines up free RNA nucleotides alongside the exposed bases on the template strand. The free bases are attracted to specific exposed bases. The mRNA strand ends up making a complimentary copy of the DNA template strand. They are then joined by RNA polymerase forming an mRNA strand

RNA polymerase moves down the DNA strand

The RNA polymerase moves along the DNA making the mRNA strand. Hydrogen bonds reform between strand and strand recoil back into double helix

RNA reaches stop signal

Reaches here and stops making mRNA and detaches from DNA and moves out of nuclear pore and to a ribosome where protein synthesis takes place

Question 6

Splicing gets rid of ______

Answer 6

introns

Question 7

Describe translation

Answer 7

Occurs in the ribosomes
Amino acids are joined together to make a polypeptide chain

mRNA attaches itself to a ribosome and transfer RNA carries amino acids to it. ATP provides energy for the bond between the amino acid and tRNA to form.

A tRNA molecule with an anticodon thats complimentary to the first codon attaches itself to the mRNA. A second tRNA molecule attaches itself to the next codon in the same way

The two amino acids attached to the tRNA molecules are joined by a peptide bond. The first tRNA molecule moves away leaving the amino acid behind

This continues until a stop signal