unit 1 KA3 - gene expression

Question 1

how many genes in a cell are expressed

Answer 1

only a fraction

Question 2

what does gene expression involve

Answer 2

transcription and translation

Question 3

what are the three types of RNA

Answer 3

mRNA, rRNA, tRNA

Question 4

what is RNA

Answer 4

RNA is single-stranded and is composed of nucleotides containing ribose sugar, phosphate and one of four bases: cytosine, guanine, adenine, and uracil

Question 5

what does mRNA do

Answer 5

it carries a copy of the DNA code from the nucleus to the ribosome

Question 6

what is mRNA

Answer 6

• it is transcribed from DNA in the nucleus and translated into proteins by ribosomes in the cytoplasm
• each triplet of bases on the mRNA molecule is called a codon and codes for a specific amino acid

Question 7

what is the strucutre of tRNA

Answer 7

• each tRNA molecule has an anti-codon (an exposed triplet of bases) at one end and an attachment site for specific amino acid at the other end

Question 8

what does tRNA do

Answer 8

• it folds due to complementary base pairing.

- each tRNA molecule carries its specific amino acid to the ribosome

Question 9

what two molecules make up the ribosome

Answer 9

rRNA and proteins

Question 10

describe the role of RNA polymerase in transcription of DNA into primary mRNA transcripts

Answer 10

• RNA polymerase moves along the DNA unwinding the double helix and breaking the hydrogen bonds between the bases
• RNA polymerase synthesizes a primary transcript of mRNA from RNA nucleotides by complementary base pairing

Question 11

what base is complementary to adenine in RNA

Answer 11

uracil

Question 12

describe splicing

Answer 12

• RNA splicing forms a mature mRNA transcript
• the introns of the primary transcript are non-coding regions and are removed
• the exons are coding regions and are joined together to form the mature transcript

Question 13

is the order of the exons changed during splicing

Answer 13

no obvi

Question 14

describe translation

Answer 14

• tRNA is involved in the translation of mRNA into a polypeptide at a ribosome
• translation begins at a start codon and ends at a stop codon
• anti-codons bond to codons by complementary base pairing, translating the genetic code into a sequence of amino acids
• peptide bonds join the amino acids together
• each tRNA then leaves the ribosome as the polypeptide is formed

Question 15

different mature mRNA transcripts are produced from the same primary transcript depending on ________.

Answer 15

which exons are retained

Question 16

different proteins can be expressed from one gene, as a result of _________.

Answer 16

alternative RNA splicing

Question 17

what is the bond that links amino acids to form polypeptides

Answer 17

peptide bonds

Question 18

which bond holds polypeptide chains together as they form the 3D shape of a protein

Answer 18

hydrogen bonds as well as the other interactions between the individual amino acids

Question 19

what determines the protein function

Answer 19

their shape

Question 20

what determines phenotype

Answer 20

the proteins produced as the result of gene expression.

Question 21

what else can influence phenotype

Answer 21

environmental factors

Question 22

describe the steps of transcription

Answer 22

• RNA polymerase moves along DNA unwinding the strand
• hydrogen bonds between base pairs break which allows the unzipping of the double helix
• as RNA polymerase breaks the bonds, it synthesizes a primary transcript of mRNA using RNA nucleotides. these form hydrogen bonds with the exposed DNA strand by complementary base pairing
• the primary transcript of mRNA is processed to produce a mature transcript of mRNA
• the mature mRNA transcript is now ready to leave the nucleus and travel to the ribosome