DNA and proteins

Question 1

DNA structure

Answer 1

2 strands of deoxyribose phosphate backbone connected the bases which are joined by phosphodiester bonds

Question 2

chromosome organisation

Answer 2

2 sister chromatids and joined by a centromere.

Question 3

the cell cycle

Answer 3

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.

Question 4

what is transcription

Answer 4

the DNA code is copied into a single strand of RNA called mRNA

Question 5

where does transcription take place

Answer 5

the nucleus

Question 6

why does it take place

Answer 6

as the DNA cannot fit through the nuclear pores.

Question 7

stages of transcription

Answer 7

1. 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.
2. RNA polymerase moves along the template strand joining free nucleotides that are complementary to exposed bases for pre mRNA.
3. the DNA bases re-join behind the RNA polymerase s it moves along.
4. 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.

Question 8

what is translation

Answer 8

the mRNA is read by a ribosome and the code is translated into the polypeptide chain.

Question 9

ribosome structure

Answer 9

made up of rRNA and proteins that has either a large or small subunit that fits either side of the mRNA strand.

Question 10

tRNA structure

Answer 10

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.

Question 11

steps of translation

Answer 11

1. ribosome attaches to the start codon on the mRNA. the tRNA moves along with the complementary anticodon. it has a specific amino acid attached.
2. 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.
3. 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.

Question 12

what can effect the DNA base sequence

Answer 12

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.