CELL CONTROL

Question 1

What is the genome? (1)

Answer 1

the genetic material of an organism

Question 2

what factors effect gene expression? (5)

Answer 2

-DNA regulatory sequences and transcription factors
-post-transcriptional modification of mRNA
-DNA methylation
-destruction of mRNA
-histone acetylation

Question 3

what factors effecting gene expression are classified as epigenetic modifications? (3)

Answer 3

-destruction of mRNA
-DNA methylation
-histone acetylation

Question 4

what is epigenetic modification? (1)

Answer 4

stable, long-term changes in the ability of a cell to transcribe its genes. though these are inherited, they are not caused by changes to the base sequence of DNA

Question 5

what is every gene associated with in terms of gene expression? (1)

Answer 5

every gene is associated with short base sequences of non-coding DNA that regulate whether the gene is transcribed (switched on or not)

Question 6

what are the types of regulatory sequences? (2)

Answer 6

-promoters
-enhancers

Question 7

what is a regulatory sequence? (1)

Answer 7

a sequence of DNA nucleotides that controls whether its target gene is transcribed or not

Question 8

what is a promoter? (1)

Answer 8

short base sequences that lie closed to their target genes. they initiate transcription by enabling RNA polymerase to bind to the gene they regulate.

Question 9

what is a enhancer? (1)

Answer 9

short base sequences that lie some distance from their target genes. They stimulate promoters causing an increase in the rate of transcription of the genes they regulate.

Question 10

what is a target gene? (1)

Answer 10

the gene a regulatory sequence regulates.

Question 11

what is a transcription factor? (1)

Answer 11

a protein, or assembly of several proteins that regulate the production of mRNA. A specific transcription factor binds to a promoter region upstream of its target gene and either promotes or inhibits the binding of RNA polymerase to the target gene.

Question 12

what can prokaryotes do to produce polypeptides? (1)

Answer 12

mRNA molecules can be produced by continuous transcription through several adjacent genes. They then process these ‘multigenic transcripts’ to generate one or more different polypeptides.

Question 13

describe eukaryote genes in terms of mRNA. (1)

Answer 13

eukaryotic cells contain base sequences that do encode for mRNA called exons, and sections that do not called introns.

Question 14

what happens during transcription? (1)

Answer 14

the exons and introns are copied into the base sequence of an RNA molecules, called pre-mRNA. This molecule is then spliced.

Question 15

What is splicing? (1)

Answer 15

the introns are removed and the exons are re-joined to form mature mRNA. This mRNA migrates to the cytoplasm where its base sequence is translated by ribosomes.

Question 16

what are the variations of mature mRNA called? (1)

Answer 16

called isoforms

Question 17

what does the destruction of mRNA involve? (1)

Answer 17

involves short regulatory RNA molecules binding to a protein to form a complex called an RNA-induced silencing complex.

Question 18

what are the types of regulatory RNA? (2)

Answer 18

-microRNA (miRNA)
- Small inhibitory RNA (siRNA)

Question 19

What is microRNA (miRNA)? (1)

Answer 19

short, single stranded RNA

Question 20

what is small inhibitory RNA (siRNA)? (1)

Answer 20

Short, double stranded RNA

Question 21

describe how miRNA leads to the destruction of mRNA. (2)

Answer 21

each miRNA molecule binds to a protein to form RISC, the miRNA within the RISC will bin to mRNA in the cytoplasm. The two RNA molecules bind by the formation of hydrogen bonds between base pairs. The sequence of bases in the two strands is not complementary, bulges appear when bases are not complementary

Question 22

what do the bulges that occur in the sequence do? (1)

Answer 22

these bulges prevent the mRNA being transcribed.

Question 23

how are siRNA molecules made? (1)

Answer 23

a RNA hydrolase, called a dicer, hydrolyses these dsRNA molecules into lengths of base pairs.

Question 24

describe how siRNA leads to the destruction of mRNA. (2)

Answer 24

bind with a protein complex to form a RISC. Proteins within the RISC unwind the RNA and remain bound to one of the strands. It is this single-stranded, antisense RNA, bound within the RISC that binds to the target mRNA. the bound mRNA is hydrolysed by another RNA hydrolase.

Question 25

what bases of a DNA nucleotide can be methylated? (2)

Answer 25

adenine and cytosine. a methyl group can be added to one of their carbon atoms.

Question 26

where are cytosine molecules most likely to be methylated? (1)

Answer 26

where the cytosine is linked by a phosphodiester bond to a guanine residue, representing CpG

Question 27

what does the presence of methylated DNA do? (1)

Answer 27

the presence of methylated DNA, especially near promoters prevents the activation of RNA polymerase. this means that the target genes of these promoters silenced. before any gene can be transcribed, its promoter must be demethylated.

Question 28

describe the function of histone. (1)

Answer 28

a structural support molecule for a chromosome

Question 29

describe the structure of histone. (2)

Answer 29

the 'tails' of the histone molecules contain the amino acid leucine, this amino residue can be acetylated.

Question 30

what happens during acetylation? (1)

Answer 30

he binding of the histones changes and they become more loosely packed. When histone is tightly packed, transcription factors and RNA polymerase cannot gain access to that region.

Question 31

what is gene imprinting? (1)

Answer 31

the stabilisation of patterns of genes being switched on or off are stabilised by DNA methylation and histone acetylation.