1.3- Gene Expression

Question 1

how can alternative RNA splicing produce different mature mRNA transcripts?

Answer 1

depending on which RNA segments are treated as exons and introns different segments can be spliced together to produce different mRNA transcripts

Question 2

what are introns?

Answer 2

Introns are non-coding regions of the primary mRNA transcript and are removed

Question 3

what are exons?

Answer 3

exons are coding regions and are spliced (joined together) to form the mature mRNA transcript- the order of exons is unchanged during splicing

Question 4

what is gene expression?

Answer 4

gene expression is the process of using information from a gene to synthesise a protein

Question 5

how do you determine a cells genotype?

Answer 5

a cells genotype is determined by the sequence of bases in its genes

Question 6

how do you determine a cells phenotype?

Answer 6

a cells phenotype is determined by the proteins that are synthesised when genes are expressed

Question 7

what are the two stages of protein synthesis and where do they take place?

Answer 7

transcription is the synthesis of mRNA from a section of DNA and takes place in the cytoplasm in prokaryotes and in the nucleus in eukaryotes.
translation is the synthesis of a protein using instructions from mRNA and takes place in the ribosomes

Question 8

what is the function of mRNA?

Answer 8

carries a copy of the genetic code from the nucleus to the ribosome

Question 9

what is the function of tRNA?

Answer 9

each tRNA molecule carries its specific amino acid to the ribosome

Question 10

what is the function of rRNA?

Answer 10

forms the ribosome with proteins

Question 11

describe stage 1 of transcription

Answer 11

the enzyme RNA polymerase moves along the gene unwinding the double helix and breaking the hydrogen bonds between the bases

Question 12

describe stage 2 of transcription

Answer 12

RNA polymerase synthesises a primary transcript of mRNA from free RNA nucleotides by complementary base pairing

Question 13

describe stage 3 of transcription

Answer 13

RNA polymerase keeps adding nucleotides from the 5’ end to the 3’ end of the growing mRNA molecule until a specific sequence of nucleotides called a stop corin is reached

Question 14

what is the result of transcription

Answer 14

the primary transcript of mRNA

Question 15

what does RNA splicing form

Answer 15

mature mRNA transcript

Question 16

describe stage 1 of translation

Answer 16

the mature mRNA transcript attaches to a ribosome in the cytoplasm

Question 17

describe stage 2 of translation

Answer 17

the start codon begins protein synthesis

Question 18

describe stage 3 of translation

Answer 18

complementary tRNA anticodons attach to the mRNA strand, bringing a specific amino acid solution o form the protein molecule

Question 19

describe stage 4 of translation

Answer 19

peptide bonds join the amino acid molecules. Each tRNA molecule leaves the ribosome once the amino acids are attached

Question 20

describe stage 5 of translation

Answer 20

a stop codon ends protein synthesis