8.DNA, Genes, Protein Synthesis Flashcards
What is a gene
Base sequence of DNA that codes for the amino acid sequence of polypeptides and functional RNA
What’s the reasoning for three bases coding for one amino acid
Only 20 different amino acids regularly occur
Each must have own code of bases on dna
Only 4 bases present in dna
If each base coded for one amino acids, only be 4 amino acids
Using three bases, 64 different codes (4^3)
What does degenerate code mean
Most amino acids coded for by more than one triplet
Features of genetic code
Degenerate code
Non overlapping
Universal
What’s a stop codon
Three bases together that don’t code for a amino acid and they mark end of polypeptide chain
What’s an Exxon and intron
Exon-coding sequences for amino acids
Intron-non coding for amino acids
What’s a locus
The particular position where a gene is located on a particular sector of dna
What’s the difference between prokaryotic dna and eukaryotic dna
Pro- short, circular and not associated with protein molecules so therefore no chromosomes
Eu-longer, linear and associated with histones to form chromosomes, mitochondria and chloroplasts contain own dna similar to prokaryotic dna
What’s a chromatid
When dna has replicated, the two identical dna molecules are joined at a single point
What’s a homologous pair
When one chromosome is from mum (maternal) and the same one is from dad (paternal)
Same chromosome but will have different alleles
What’s an allele
Alternative form of gene
Two different forms of genes-different forms are alleles
Allele inherited from each parent
What’s the danger of change in base sequence of gene
Produces new allele =mutation
Different polypeptide due to different amino acid sequence
Different protein
May not be functional
If enzyme produced, new shape not fit substrate
Enzyme not function=serious consequence for organism
What is mRNA
Messenger rna
Transfers dna code from nucleus into cytoplasm leaves via nuclear pores
What’s a genome
Complete set of genes in a cell, including those in mitochondria/chloroplasts
What’s a proteome
Range of proteins produced by genome, called complete proteome where proteome refers to proteins produced by a given type of cell under certain set of conditions
What makes up the mononucleotide of ribonucleic acid
Ribose (pentose sugar)
An organic base (A,G,C,U
Phosphate group
What is messenger rna structure
- Long strand arranged in single helix
- Base sequence is determined by bases on length of dna is process called transcription
- structure is suited to function as possess information in form of codons and the sequence determines specific polypeptide made
What is tRNA structure
- Relatively small molecule made up of around 80nucleotides
- Single stand folded into clover leaf shape one end extends beyond the other (point of amino acid attachment)
- anticodon at opposite end-three coding bases
What happens during transcription
- Enzyme acts on specific region of DNA, two strand separate expose nucleotide bases in that region
- template strand baes pair with complimentary bases from pool
- enzyme rna polymerase moves along strand and joins nucleotides together to form pre mRNA molecule
- as RnA polymerases adds one nucleotide at a time, DNA strands rejoin behind it, only 12 bases exposed at once
- when RNA reaches stop triplet it detached, pre mRNA completed
What happens in splicing
- Transcription results in pre-mRNA which contains introns and exons
- introns prevent synthesis of polypeptide
- introns are removed and functional Exxon’s are joined together in process called splicing
- leave nucleus via nuclear pore in nuclear envelope, attach to ribosome in cytoplasm
- only happens in eukaryotic cells
What happens in translation/synthesising polypeptide
- ribosome attaches to one end of mRNA
- tRNA molecule complimentary anticodon sequence moves to ribosome and pair with codon on mRNA, tRNA carries specific amino acid
- tRNA molecules pairs with next codon on mRNA, ribosome moves up mRNA bringing together two tRNA molecules at any one time an pairing them with mRNA
- amino acids are joined by peptide bonds using enzyme and atp
- as the second and third amino acids are joined the first tRNA is released and free to collect another amino acid from pool in cell
- process continues until polypeptide chain is built
- synthesis continues until ribosome reaches stop codon and last tRNA is released
How is a protein assembled
- sometimes only polypeptide chain is a functional protein, sometimes many are linked together to be functional
- secondary folding, tertiary folding, non proteins being added to quarternary
