DNA and proteins Flashcards
DNA structure
2 strands of deoxyribose phosphate backbone connected the bases which are joined by phosphodiester bonds
chromosome organisation
2 sister chromatids and joined by a centromere.
the cell cycle
cells replicate and divide in order to increase cell number for growth. cell growth is G2. further cell growth is G1 and DNA synthesis is S phase.
what is transcription
the DNA code is copied into a single strand of RNA called mRNA
where does transcription take place
the nucleus
why does it take place
as the DNA cannot fit through the nuclear pores.
stages of transcription
- RNA polymerase binds to the start codon. DNA helicase binds breaking the hydrogen bonds on the section of DNA containing the gene for the desired protein. bases are exposed.
- RNA polymerase moves along the template strand joining free nucleotides that are complementary to exposed bases for pre mRNA.
- the DNA bases re-join behind the RNA polymerase s it moves along.
- the RNA polymerase will stop and detach when it reaches the stop codon.
the pre mRNA is spliced to remove introns before it leaves the nuclear pore.
what is translation
the mRNA is read by a ribosome and the code is translated into the polypeptide chain.
ribosome structure
made up of rRNA and proteins that has either a large or small subunit that fits either side of the mRNA strand.
tRNA structure
short single strand of RNA. folded into a clover leaf shape and held by hydrogen bonds between bases. amino acid binding site. anticodon binding site.
steps of translation
- ribosome attaches to the start codon on the mRNA. the tRNA moves along with the complementary anticodon. it has a specific amino acid attached.
- the ribosome moves along to the next codon. process is repeated and the enzyme catalyses the condensation reaction between the amino acids to join them with peptide bonds.
- the ribosome continues to move along the mRNA and the tRNA arrives with amino acids until there reach a stop codon. they all detach a polypeptide chain is formed.
what can effect the DNA base sequence
there may be a mutation which means bases can either be deleted or added. this means that the bases wont be complementary so a different protein or a damaged protein could be made.