DNA and protein synthesis Flashcards
What is a gene?
A section of DNA located at a particular position, called a locus.
What does a gene do?
Codes for the amino acid sequence of polypeptides or functional RNA, including rRNA and tRNA.
Scientists’ reasoning for minimum 3 bases that coded for each amino acid.
20 amino acids regularly occur in proteins, each amino acid has its own base code, only 4 bases, 4^3 = 64 which is greater than 20.
DNA is known as _____ code and what does this mean?
Degenerate code which means that most amino acids are coded for by more than one triplet.
Why is the code for DNA a degenerate code?
Because it means that any mutations have a higher chance of not affecting which amino acid is translated.
What does each DNA sequence have at start and end?
At the start there is always the same triplet that codes for methionine. If the first methionine is not part of the final polypeptide, it is later removed. At the end, there is a stop code.
What are the features of DNA code?
It is universal (indirect evidence for evolution).
It is non-overlapping.
What is an intron?
Non-coding sequences that separate exons within genes.
What is an exon?
A coding sequence in a gene.
DNA structure in prokaryote
DNA molecules are short, circular and not associated with proteins. No chromosomes.
DNA structure in eukaryote
DNA molecules are longer, linear and occur in association with histones to form chromosomes.
DNA in mitochondria and chloroplasts are similar to that of prokaryotes.
What is a triplet?
A sequence of 3 bases that codes for an amino acid.
What is a homologous pair?
A pair of chromosomes where one comes from mother and one comes from the father. They contain the same genes but not necessarily the same alleles.
What is an allele?
One of a number of alternative forms of a gene. One inherited from each parent.
What is a genome?
The complete set of genes in a cell, including those in the mitochondria and chloroplasts.
What is a proteome?
The full range of different proteins produced by the genome.
Describe the process of transcription
- DNA helicase enzyme acts on the DNA, separating strands so the nucleotides are exposed.
- Free complementary nucleotides bond to the pair onto the template strand and the enzyme RNA polymerase joins the nucleotides together to form a pre-mRNA molecule.
- Adenine links to uracil, thymine links to adenine, guanine links to cytosine and cytosine links to guanine,
- DNA strands close as each nucleotide is added onto the chain by RNA polymerase.
- Keeps going until a stop triplet code.
- Pre mRNA is then spliced (introns removed and exons reattached) before exiting nucleus through pore.
Describe process of pre-mRNA splicing in eukaryotes
Base sequences of introns are removed and the exons are joined together. Prokaryotes do not have introns. After this process the mRNA molecule leaves the nucleus via nuclear pore.
Describe process of translation
- Ribosome attaches to starting codon at one end of mRNA.
- tRNA with complementary anticodon sequence pairs with codon on mRNA and carries specific amino acid.
- tRNA with complementary anticodon binds to next codon on mRNA, carrying another amino acid.
- Ribosome moves along mRNA, bringing together two tRNA molecules. The two amino acids then are linked by peptide bond and enzyme and ATP.
- Ribosome moves onto third codon and links 2nd and 3rd amino acids and first tRNA is released from its amino acid and can collect another.
- Continues until stop codon is reached and polypeptide chain is complete.
What is a locus
A point on a DNA molecule where a gene is located
mRNA structure
Single helix of RNA. Exposed base pairs.
tRNA structure
One strand of RNA folded into clover shape.
Site for amino acid to bond and a unique anticodon.
Addition mutation
Changes triplets further on in DNA sequence (frame shift mutation), affects function of polypeptide
Deletion mutation
Changes triplets further on in DNA sequence (frame shift mutation), affects function of polypeptide
Silent mutation
Mutation does not change amino acid sequence due to degen coding
Missense mutation
Single amino acid altered
Nonsense mutation
Creates premature stop codon therefore incomplete polypeptide produced.
Inversion mutation
When section of gene is cut then resealed after 180 degree inversion.
Duplication of genee
Non harmful because original version stays intact
Non-dysjunction
In meiosis chromosomes do not separate.
