DNA -> Protein (2.7, 7.2, 7.3) Flashcards
What are the three bases that code for an amino acid called?
Triplet on DNA
Codon on mRNA
Anticodon on tRNA
What is transcription?
Making a copy (mRNA) of a section of DNA. It is the first stage of protein synthesis.
Describe the process of transcription.
RNA polymerase unwinds a section of the DNA in the nucleus. RNA polymerase adds free nucleotide units forming a single strand of mRNA that is complementary to the template strand (therefore it is the same as the coding strand). It is synthesised in a 5’ to 3’ direction. When RNA polymerase reaches the terminator, the enzyme and the mRNA strand detach and the DNA rewinds.
Define a promoter.
A promotor is a non-coding sequence of DNA that is responsible for the initiation of transcription. It is the binding site of RNA polymerase (the enzyme that catalyses the synthesis of RNA).
What is translation?
The synthesis of polypeptides on ribosomes. The second stage of protein synthesis.
Describe the process of translation.
1) Initiation.
The assembly of the newly synthesised mRNA (with the start codon AUG), tRNA (with the start amino acid) and ribosomes.
2) Elongation.
tRNA brings the appropriate amino acid to the ribosome. The anticodon on the tRNA matches with the codon on the mRNA. The amino acid is joined to the polypeptide chain. The ribosome moves the mRNA strand along and the next tRNA falls into place.
3) Termination.
The ribosome reaches a stop codon. The polypeptide chain disconnects from the ribosome. Thus a protein is synthesised.
Describe tRNA activation.
A tRNA-activating enzyme binds ATP to the amino acid to form an amino acid–AMP complex. The amino acid is then coupled to tRNA and the AMP is released – the tRNA molecule is now “charged”.
What is the Lac Operon Model?
F. Jacobs and J. Monod put forward a hypothesis to explain why E. coli produced the enzyme galactosidase (which breaks down lactose) only when lactose was present.
The section of the DNA that codes for the enzyme is called the Structural gene. Near this is another section of DNA called the Operator gene. The Operator gene activates the Structural gene when the enzyme is required.
The Operator gene is controlled by the Regulator gene. The Regulator gene produces a Repressor substance which turns the Operator gene off (so no enzyme is made). When the enzyme is needed the repressor substance is inhibited.
Define epigenetics.
The study of environment that turn genes on and off and affect how cells read genes. It is caused by the modification of gene expression and not changes to the DNA sequence.
What are the two main mechanisms of epigenetics?
DNA methylation:
The addition of methyl groups to cytosine and adenine in DNA. This acts to suppress gene transcription. It varies throughout a lifetime and can be affected by the environment, age and lifestyle choices. Methylation patterns are different in healthy and diseased cells so analysis can help to identify disease marker genes.
Histone modification:
DNA is wrapped around histones so alterations to the histone can affect the activity of the DNA.
