Transcription and Translation - A2 Biology (Unit 5)

• Transcription
• Splicing
• Transcription
• Protein Synthesis
• siRNA
• Translation Factors
• Oestrogen
• Mutations

Transcription is the process where the information in DNA is transferred to the Ribosomes in the Cytoplasm in the form of mRNA.

1-   The hydrogen bonds between Nucleotide bases break, and the double helix of the DNA begins to unwind.

2- RNA Polymerase recognises a 'Start' code on the strand of DNA and attaches itself to the DNA at this point.

3- RNA Polymerase moves along the strand of DNA and catalyses the production of mRNA molecules, where free Nucleotide bases attach to the complimentary bases on the DNA strand. HOWEVER - Instead of Thymine, Uracil forms a bond with Adenine.

5- Splicing occurs to remove Introns from the Pre-mRNA to produce Mature mRNA.

4- After Transcription is completed, the mRNA moves out of the Nuclear pores and into the Cytoplasm for Translation. The Double-helix of the DNA is reformed.

• DNA
• Double helix
• Hydrogen bonds (H+ Bonds)
• Unwinds
• Nucleotide bases
• RNA Polymerase
• Start Code
• Complimentary
• Splicing
• Introns
• Exons
• Pre-mRNA
• Mature mRNA (mRNA)
• Single-Stranded (mRNA)
• Double-Stranded (DNA)
• Nucleus
• Nuclear Pores

Translation is the process where mRNA is used to combine with tRNA in order to produce a Polypeptide chain of Amino Acids.

1- mRNA from Transcription attaches to a Ribosome.

2- tRNA molecules carry Amino Acids to the Ribosome, where they Amino Acids attach to the Amino Acid binding site on the tRNA.

3- The tRNA Molecule has a complimentary anti-codon to the codon on the start of the mRNA strand and binds with the mRNA.

4- A second tRNA molecule binds to the next codon on the mRNA, there are now 2 Amino Acids present and so, a peptide bond forms between them.

5- Process is repeated until a 'Stop code' is reached, and the polypeptide chains moves away from the Ribosome.

• mRNA
• tRNA
• Cytoplasm
• Ribosome
• Amino Acids
• Codon
• Anti-Codon
• Complimentary
• Start Code
• Stop Code
• Peptide Bond
• Clover Shape
• Amino Acid Binding Site
• Moves away
• Polypeptide Chain
• Protein Synthesis

Transcription Factors control the Transciption of Target Genes

• Transcription Factors move from the Cytoplasm to the Nucleus
• They bind to specific DNA sites near the start of their Target Genes
• They control expression by controlling the rate of transcription.
• Activators = increase the rate of transcription. E.G they help RNA polymerase bind to the start of the Target Gene.
• Repressors = Decrease the rate of transcription = E.G Bind to the start of the target gene and preventing RNA Polymerase from binding and so stopping transcription in itself.

Oestrogen is an example of a Transcription Factor.

• Control
• target genes
• bind
• near target gene
• prevent transcription
• RNA Polymerase
• Activators
• Repressors
• Cytoplasm
• Nucleus

• Oestrogen also affects Translation.

1- Binds to Transcription factor called 'Oestrogen-Receptor' = forming an Oestrogen-Oestrogen receptor complex.

2- The Complex moves into the nucleus and binds to a specific DNA site near the target Gene.

3- Oestrogen can then act as an Activator or a Repressor.

4- Level of Oestrogen affects the rate of transcription.

• Transcription Factor
• Transcription
• Translation
• Binding
• Near Target Gene
• Oestrogen
• Oestrogen-Receptor
• Oestrogen-Oestrogen Receptor Complex
• Activator
• Repressor
• Nucleus

siRNA is Small Interfereing RNA which can interfere with the expression of certain genes.

1- siRNA is short, double-stranded RNA and can interfere with gene expression.

2- Their bases are complimentary to those near a target Gene.

3-siRNA can interfere with both Transcription and Translation.

4- It does so through RNA interference, where:

• siRNA binds to the target mRNA in the cytoplams.
• The proteins attached to the siRNA cut up the mRNA and it can no longer be translated.
• Prevents expression of the specific gene as its protein can no longer be made during translation.

• siRNA
• gene expression
• short
• double stranded
• complimentary bases
• binds
• near target gene
• RNA interference
• cuts up
• no longer useful
• transcription
• protein
• inhibited

Any change to the base sequence of DNA is called a mutation. They can be caused by Errors, Mutagenic agents. Errors include Substitution or Deletion.

• Not all mutations affect the order of amino acids.
• A substitution can result in the production of a different amino acid due to the degenerate nature of DNA where many amino acids can be coded for by more than one triplet code.
• Deletions, however, will always results in a differerent Amino Acid, due to the frameshift that would occur when a base is removed.
• Mutagenic agents occur spontaneously - however, some things may increase the rate of mutations.
• Such as: Ultraviolet radiation, Ionising radiation, Chemicals, some viruses.
• They do this by: Acting as a base, Altering Bases and Changing the structure of DNA.

• Change
• base sequence
• mutation
• errors
• substitution
• deletion
• amino acid
• protein
• triplet code
• Frameshift
• mutagenic agents
• radiation
• chemicals
• viruses
• acting as a base
• altering bases
• changing DNA structure.
• Degenerate Code