Biology.

What is a DNA molecule typically referred to as?

Semi-Conservative.

Why is a DNA molecule referred to as Semi Conservative?

This is because every new DNA molecule consists of one original parent strand and one newly synthesised strand.

Explain the role of DNA helicase.

DNA Helicase binds to the double helix and moves along the polynucleotide strands, breaking the hydrogen bonds between complementary purine and pyrimidine base pairs.

What happens to the DNA double helix after DNA helicase does its job?

The Double Helix unzips and unwinds, exposing the nitrogenous bases on both sides.

What do BOTH the separate strands act as?

Template strands.

What happens to the exposed bases?

Free floating activated DNA nucleotides are attracted to exposed bases via complementary base pairings.

How many hydrogen bonds between Adenine and Thymine?

two.

How many hydrogen bonds between Cytosine and Guanine?

three.

What is the first step taken by DNA polymerase?

DNA polymerase moves down the template strand, catalysing the formation of a new strand.

What is the second step taken by DNA polymerase.

DNA polymerase forms Phosphodiester bonds between adjacent nucleotides through condensation reaction, forming sugar-phosphate backbone.

Why is DNA polymerase so specfic?

Due to it’s active site, It can only bind to and attach fresh nucleotides to the free 3’ hydroxyl end on a developing strand.

Okazaki fragments.

Short, Newly synthesised DNA fragments formed discontinuously on the lagging strand.

DNA ligase.

Enzyme responsible for joining Okazaki fragments together by catalysing formation of phosphodiester bonds.

DNA polymerase and role with Lagging strand?

DNA polymerase binds and builds backwards in short sections, producing Okazaki fragments.

How many rules within the Genetic code.

4

Name the rules.

Triplet code

Degenerate

universal

Non-overlapping

Explain Triplet Code.

Every three consecutive nucleotide bases code for a single amino acid.

On a molecule of mRNA, what is this triplet code typically referred to as?

A codon.

Define Degenrate.

More than one codon can code for a single Amino acid.

How many possible triplet codon combinations are there?

64

Define non overlapping

Each base in the sequence is read strictly once as part of its specific triplet codon.

Define universal

The same specfic triplet codon codes for the same amino acid in all living organisms.

How does the degenerate nature of the code protects an organism from mutations?

If a single base is swapped, the new codon may still code for the same amino acid. This means the primary structure remains completely unaltered, resulting in a silent mutation.

Where does Transcription take place in?

The Nucleus.

Define Introns

Non-coding sections of DNA/RNA that are located within a gene.

Define externs

Coding sections of DNA/RNA that consist of sequence for an amino acid.

Define Splicing.

A specialised enzyme complex that cuts out and removes all introns from pre-mRNA transcript and splices remaining extrons together into a continuous chain.

Explain the Initiation step at the start of Translation.

Mature mRNA binds to small sub-unit of ribosome. Ribosome covers exactly two codes at one time.

Role of tRNA molecule.

tRNA molcule carries an amino acid approaches, it’s anticodon binds to the complementary codon on the mRNA molecule via temporary hydrogen bonds.

Role of Peptidyl transferase.

Peptidyl transferase is an enzyme that catalyses the formation of a peptide bond between amine group of one amino acid and carboxyl of the next via condensation reaction.

Describe movement of ribosome.

Ribosome moves strictly one codon at a time along the mRNA strand.

What happens to empty tRNA molecules.

They are forced out through the E-site to be recharged in the cytoplasm with a new amino-acid.

Explain Termination in Translation.

Ribosome encounters stop codon.

Stop codons do not code for an Amino acid.

They bind a release factor that causes ribosomes to detach.

Typical stop codon.

UAA, UAG, UGA

What enzyme builds peptide bonds between adjacent amino acids during translation.

Peptidyl Transferase.