Key area 3- Gene expression

Question 1

What is the cell genotype?

Answer 1

.It is the genetic composition of a cell
.It is determined by the sequence of DNA bases in its genes

Question 2

What is the cell phenotype?

Answer 2

.It is determined by the proteins that are produced when genes are expressed
.It can also be influenced by environmental factors

Question 3

What are the two stages involved in gene expression?

Answer 3

.Transcription
.Translation

Question 4

What is a gene?

Answer 4

.A sequence of bases which codes for a specific protein

Question 5

What does the order of bases in DNA determine?

Answer 5

.The sequence of amino acids in the protein coded for

Question 6

What chains hold together the sequence of amino acids?

Answer 6

.Polypeptide chains, which also determine the structure, shape, and function of the protein produced

Question 7

Describe the features of RNA

Answer 7

.Ribose sugar (rather than deoxyribose present in DNA)
.Phosphate
.Base (cytosine, guanine, adenine, uracil instead of thymine)
.Single stranded

Question 8

What are the three types of RNA?

Answer 8

.mRNA (messenger RNA)
.rRNA (ribosomal RNA)
.tRNA (transfer RNA)

Question 9

Describe Messenger RNA

Answer 9

.It carries a copy of the DNA code from the nucleus to a ribosome
.It is made by transcription
.Each codon, triplet code of DNA, on the mRNA molecule is transcribed in the nucleus
.mRNA is translated into proteins by ribosomes in the cytoplasm.
.Each codon codes for a specific amino acid

Question 10

Describe Transfer RNA

Answer 10

.It is folded due to complementary base pairing
.There are only three bases exposed in the 3D structure, this exposed triplet of bases forms an anti-codon
.It is made of two ends, one is the anti-codon which are complementary and bind to a specific mRNA codon, and one is the attachment site which is for a specific amino acid
.It carries a specific amino acid to the ribosome

Question 11

Describe Ribosomal RNA

Answer 11

.rNA and proteins form the ribosome
.They remain as free ribosomes in the cytoplasm where they translate mRNA into protein

Question 12

What are the differences between RNA and DNA?

Answer 12

.DNA= deoxyribose sugar, base thymine, double stranded and long with many genes
.RNA= ribose sugar, base uracil, single stranded and short as one gene long

Question 13

What are the stages in Transcription?

Answer 13

.RNA polymerase moves along DNA unwinding the double helix and breaking hydrogen bonds between the bases
.RNA polymerase synthesises a primary transcript of mRNA from RNA nucleotides by complementary base pairing, uracil in RNA is complementary to adenine
.RNA polymerase can only add nucleotides to the 3’ end of the newly synthesised mRNA transcript
.RNA polymerase joins the RNA nucleotides together to form a new sugar-phosphate backbone of the primary transcript of mRNA
.The mRNA becomes separated from the DNA template, and is called the primary transcript of mRNA. The primary transcript of mRNA which codes for the polypeptide chain of amino acids is fragmented

Question 14

What are introns?

Answer 14

.They are non-coding regions of genes and are cut and therefore removed during RNA splicing

Question 15

What are exons?

Answer 15

.They are coding regions of genes which are joined together to form mRNA, with a continuous sequence of nucleotides which is called the mature transcript of mRNA
.The order of exons are unchanged during splicing

Question 16

What does the process of RNA splicing form?

Answer 16

.A mature mRNA transcript

Question 17

What is the mature transcript of mRNA?

Answer 17

.The continuous sequence of nucleotides of mRNA formed from exons
.It moves from the nucleus through the cytoplasm to a ribosome

Question 18

What are the stages of RNA splicing?

Answer 18

.It forms a mature mRNA transcript
.The introns of the primary transcript are non-coding regions of genes and are cut out and removed. They are found between the exons.
.The exons are coding regions and are joined/spliced together to form mRNA with a continuous sequence of nucleotides, this is called the mature transcript of mRNA.
.The order of the exons is unchanged during splicing
.The mature transcript of mRNA moves from the nucleus through the cytoplasm to a ribosome

Question 19

What are the stages of translation?

Answer 19

.mRNA binds to the ribosome, translation begins at a start codon
.Each tRNA picks up specific amino acids in the cytoplasm and carries it to the ribosome
.Each tRNA anti-codon binds to a complementary codon on the mRNA lining up the amino acids in a specific order, translating the genetic code into a sequence of amino acids
.Peptide bonds form between the amino acids to from a growing polypeptide chain
.Each tRNA then leaves the ribosome as the polypeptide forms
.Translation ends at a stop codon
.When the polypeptide chain is complete it detaches from the ribosome

Question 20

What translation is tRNA involved in?

Answer 20

.It is involved in the translation of mRNA into a polypeptide at a ribosome

Question 21

How does translation begin?

Answer 21

.With a start codon

Question 22

What mRNA codons act as stop codons?

Answer 22

.UAA
.UAG
.UGA

Question 23

What are the three binding sites of ribsomes on tRNA?

Answer 23

.Site 2 holds the tRNA carrying the amino acids and growing polypeptide chain
.Site 3 holds the tRNA carrying the next amino acid
.Site 1 discharges the tRNA from the ribosome once the amino acid has become part of the polypeptide chain

Question 24

What bonds join the amino acids together?

Answer 24

.Peptide bonds

Question 25

Where does translation occur?

Answer 25

.In the nucleus

Question 26

What happens when the mRNA transcript leaves the nucleus?

Answer 26

.It is translated into a polypeptide by tRNA at a ribsome
.tRNA folds it due to base pairing to form a triplet anti-codon site and an attachment site for a specific amino acid

Question 27

What does the sequence of amino acids determine?

Answer 27

.The structure and function of the protein