Gene expression

Not finished

Phenotype

The visible characteristics of an organism

What determines an individuals phenotype?

Genes (proteins)

What controls gene expression?

Transcription and translation

Protein synthesis

When a gene is expressed

Diagram: DNA nucleotide

Diagram: RNA nucleotide

In what four ways does RNA differ from DNA?

• RNA contains the base uracil whereas DNA contains the base thymine

• RNA is found in the cytoplasm and the nucleus whereas DNA is only found in the nucleus

• RNA is made of ribose sugar whereas DNA is made of deoxyribose sugar

• RNA is single stranded whereas DNA is double stranded

mRNA

This carries a copy of the DNA code from the nucleus to the ribosome

tRNA

This takes a specific amino acid from the cytoplasm to the ribosome depending on the anti-codon

rRNA

This forms the ribosome and proteins

How does the genetic code from the DNA get to the ribosomes?

The mRNA strand takes the complementary code out of the nucleus and travels through the cytoplasm to get to the ribosomes

Transcription

The synthesis of the mRNA strand from a section of DNA, controlled by RNA polymerase

What are the six stages of transcription?

1. RNA polymerase moves along the gene, unwinding and unzipping (breaking the hydrogen bonds between the bases) the DNA double helix

2. Free mRNA nucleotides join with the complementary nucleotides on the DNA template strand, this is controlled by RNA polymerase

3. Weak hydrogen bonds form between base pairs

4. Strong chemical bonds form between the sugar of one RNA nucleotide and the phosphate of another

5. Weak hydrogen bonds break between the complementary base pairs, allowing mRNA to peel off the DNA

6. This molecule is called a primary mRNA transcript

Diagram: transcription

Diagram: RNA splicing

Diagram: translation

Diagram: protein structure

Introns

Non-coding regions of a gene that are cut out and removed from the primary mRNA transcript

Exons

Coding regions of a gene that are retained and joined together to form the mature mRNA transcript

What are the four stages of RNA splicing? (this is apart of transcription)

1. Introns (non-coding regions) are removed from the primary mRNA transcript

2. Exons (coding regions) are retained

3. Exons are spliced together to form the mature mRNA transcript

4. The mature mRNA transcript passes out of the nucleus into the cytoplasm, where it joins to a ribosome

Translation

The synthesis of a protein under the control of mRNA in the cytoplasm

RNA splicing (this is apart of transcription)

When the introns of the primary mRNA transcript are removed and the exons are retained in order to form the mature mRNA transcript

Codon

Every three bases (triplets) on the mature mRNA transcript

Anti-codon

Every three bases (triplets) on the tRNA molecule that correspond to a particular amino acid

What is the mRNA and tRNA code for the DNA code of: AGCT

mRNA: UCGA

tRNA: AGCU

What are the eight stages of translation?

1. A ribosome binds to the 5’ end of the mature mRNA transcript at a start codon

2. tRNA molecules have an anti-codon and an amino acid attachment site

3. tRNA molecules collect a specific amino acid

4. tRNA molecules carry the amino acid to the ribosome (where mRNA is attached)

5. The anti-codon of the tRNA molecules pairs up with a codon on the mRNA strand

6. This is repeated for many tRNA molecules and amino acids are brought adjacent to each other in the correct sequence

7. Peptide bonds form between adjacent amino acids to produce a polypeptide chain

8. A stop codon is reached which stops translation

Where does transcription occur?

In the nucleus

Where does translation occur?

In the cytoplasm

Where does (alternative) RNA splicing occur?

In the nucleus

Diagram: alternative RNA splicing

Alternative RNA splicing

The same primary mRNA transcript can make several different mature mRNA transcripts as different exons are retained within the transcript (this changes the combination of exons)

How many genes are required to make a variety of proteins?

Just one

What are the four elements that all proteins contain?

• Carbon

• Hydrogen

• Nitrogen

• Oxygen

What bonds hold adjacent amino acids together?

Peptide bonds

What bonds hold different amino acids together in order to create a fold?

Hydrogen bonds

What determines the function of a protein?

The shape of the protein

How does DNA determine the shape and function of a protein?

Sequence of bases on the DNA strand > sequence of bases on the mRNA strand > sequence of bases on the tRNA molecule > sequence of amino acids > function of a protein

A gene

A section of DNA that codes for a protein