Gene structure and regulation Flashcards
Define gene
is a length of DNA which codes for a specific protein
Define degenerate
When one amino aid may be represented by more than one triplet
Every protein that is made in our body has a corresponding …
gene associated with it because the gene is what provides the instructions as to what the amino acid sequence of the protein is.
Define the genetic code
is a set of rules that define how info in nucleic acid (RNA and DNA) is translated into proteins and functional RNA molecules. The info in DNA and RNA is stored in a 3 letter code of nucleotide, each triplet code for one amino acid and may provide a specific instruction. So code determines which sequence of nucleotide are translated unto which amino acid.
Protein synthesis from genes
Describe transcription
Gene found on the DNA in nucleus is ‘copied’ in the form of a mobile form of genetic material called messenger RNA. The mRNA will leave the nucleus and enter the ribosome.
Protein synthesis from genes
Define translation
Is the conversion of a message from one language to another
Protein synthesis from genes
Define transcription
Copy a piece of text down
Protein synthesis from genes
Describe translation
The genetic code is ‘translated’ into an amino acid sequence. The mRNA arrives at the ribosome, which synthesizes a polypeptide whose amino acid sequence is dictated by the genetic code on the mRNA.
Protein synthesis from genes
Characteristics of transcription
- To form copy of gene we use RNA polymerase.
- The enzymes unwinds the DNA and synthesises an RNA strand complementary to the 3’ -> 5’
- The RNA polymerase ‘reads’ the DNA in a 3’ –> 5’ direction but synthesises the RNA strand in a 5’ -> 3’ direction (antiparallel)
Protein synthesis from genes
Transcription The pre-mRNA is modified in three ways - - -
- Segments on the pre-mRNA are spliced and removed from the pre-mRNA and the remaining pieces join together. Introns are removed, exons joins together
- A methyl ‘cap’ is added to the 5’ end of the RNA strand
- A poly-A tail (a string of adenine- RNA nucleotide is added ti the 3’ end of the RNA strand)
After this the product is mRNA, known as post-transcription modifications
Protein synthesis from genes
Translation What occurs - - -
- The mRNA arrives at the ribosome
- tRNA molecule with the amino acids attached anneals to the mRNA codons via their complementary tRNA antibodies (ie tRNA anitcodon AAA will anneals mRNA codon UUU)
- The amino acids that arrive at the ribosome on their tRNA will detach form the tRNA and be polymerised to form the polypeptide
Protein synthesis from genes
Gene regulation
How do all cells have the same genome (genes) but do different things?
This is because different cells express different genes; some are switched on whereas other genes are switched off via a protein blocking the promoter region.
Protein synthesis from genes
Gene regulation
Why do all cells have the same genome (genes) but do different things?
prevent cells from producing proteins that arent needed by cell therefore saving resources. Also prevents producing proteins that harm the organism.
Protein synthesis from genes
Gene regulation
Define transcription factors
DNA binding proteins that affect the rate of transcription
Protein synthesis from genes
Gene regulation
Signalling molecules
may bind to receptor on the cell, which may cause the expression of a gene or the inhibition of that gene
Protein synthesis from genes
Gene regulation
Regulatory genes
Transcription factors, and other proteins in the cell that act to regulate the expression of other genes are themselves coded by regulatory genes
Protein synthesis from genes
Gene regulation
Define Lac operon
This is the mechanism by which a bacterial gene that synthesisies an enzyme that metabolises lactose is regular.
Protein synthesis from genes
Gene regulation
Lac operon regulatory mechanism is designed to..
ensure that the gene is expressed only when there are sufficient amounts of lactose present in the cell.
Protein synthesis from genes
Gene regulation
Lac operon
What occurs when there is no lactose
The inhibitory transcription factor binds onto the operator. This inhibits the ability of RNA polymerase to bind onto the promoter.
Protein synthesis from genes
Gene regulation
Lac operon
What occurs when there is lactose
lactose binds to the transcription factor, changing its conformation. This changes the binding site of the transcription factor. causing it to detach from the operator. Subsequently, the RNA polymerase is able to bind to the promoter region of the gene and to transcribe the gene.
