DNA, RNA and protein synthesis Flashcards
DNA in eukaryotic cells
linear DNA molecules that exist as chromosomes, really long (so wound up, around proteins called histones - which also help support the DNA)
DNA in prokaryotic cells
shorter, circular, isn’t wound around histones, it is supercoiled
what does a gene code for
polypeptide or functional RNA
what is a genome
complete set of genes in a cell
what is a proteome
full range of proteins that the cell is able to produce
what is functional RNA
RNA that perform special tasks during proteinsynthesis
how is an amino acid coded for
sequence of 3 bases called a triplet
what is removed during protein synthesis
introns
what is an allele
different versions of the same gene that code for different versions of the same polypeptide
how many pairs of chromosomes do human cells have
23
what is a homologous pair
pairs of matching chromosomes (same size, same genes but could have different alleles)
types of RNA
messenger RNA (mRNA) transfer RNA (tRNA)
messenger RNA
made during transcription, carries genetic code from DNA to ribosomes (where its used to make a protein during proteinsynthesis), single polnucleotide strand, groups of 3 bases = codons/triplets
transfer RNA
involved in translation, carries amino acid used to make proteins to the ribosomes, clover shape due to hydrogen bonds between base pairs, amino acid binds to one end, anticodon at one end (specific sequence of tree bases)
what is the first stage of protein synthesis
transcription
what is transcription
making an mRNA copy of a gene from DNA
where does transcription take place in eukaryotic cells
nucleus
where does transcription take place in prokaryotic cells
cytoplasm (as they do not have a nucleus)
stages of transcription
1) RNA polymerase attaches to the DNA double-helix at the beginning of a gene, and breaks the hydrogen bonds between the genes
2) this causes the strands to seperate and uncoil, exposing some of the bases and the acts as a template to make an mRNA copy from
3) RNA polymerase lines up free RNA nucleotides alongside the exposed bases and complementary base pairing takes place, meaning an mRNA strand of complementary pairing is made
5) the free RNA nucleotides are joined by
when does transcription stop?
when RNA polymerase reaches a ‘stop’ codon, it stops making RNA and detaches from DNA
how does mRNA move out of eukaryotic cells
moves through the nuclear pore and attaches to a ribosome in the cytoplasm
what form of mRNA contains introns and exons
pre-mRNA (in eukaryotic cells)
what is removed during splicing
introns
what process removes introns
splicing
what cells mRNA doesn’t contain introns
prokaryotic
what is the next stage of protein synthesis
translation
what is translation
when amino acids are joined together to make a polypeptide chain, following the sequence of codons carried by the mRNA
where does translation occur
at the ribosomes in the cytoplasm
what happens during translation
1) mRNA attaches itself to a ribosome , and tRNA molecules carry amino acids to it.. ATP provides the energy required to form the bonds between the tRNA and amino acids
2) a tRNA molecule (carrying an amino acid) with an anticodon complimentary to the first codon of the mRNA attaches to the mRNA by specific base pairing
3) a second tRNA molecule attaches to the next codon in the same way
4) the 2 amino acids on the tRNA molecules are joined by a peptide bond, and the first tRNA molecule moves away leaving behind the amino acid
5) this process continues to produce a chain of linked amino acids, until theres a stop signal on the mRNA chain
6) the polypeptide chain moves away from the ribosome and translation is complete
what is the genetic code
sequence of base triplets in mRNA that code for a specific amino acid
genetic code features
non-overlapping, degenerate, universal
base triplets function
each triplet is read in sequence, they are seperate, and don’t share their features
what does degenerate mean
there are more possible combinations of triplets than there are amino acids - 20 amino acids, 64 possible triplets - which means some amino acids are coded for by more than one base triplet
start and stop codons
code for the start and stop of the production of the protein, found at the beginning and end of the mRNA
what does universal mean
same specific base triplets code for the same amino acids in all living things
