20: Gene expression

Question 1

gene mutation

Answer 1

• alteration of a base in the sequence, likely to occur during dna replication
• if different amino acid, hydrogen and ionic bonds formed in diff places, fold in diff places, diff 3d shape, nonfunctioning protein

Question 2

mutagenic agents

Answer 2

1. high energy and ionising radiaton. damage and disrupt dna
2. carcinogens. chemical that interferes with structure of dna, interferes with transcription

Question 3

6 types of gene mutations

Answer 3

• addition (frame shift)
• substitution
• deletion (frame shift)
• inversion (detach then rejoin inverted)
• translocation (section of bases detach and attach to different chromosome)

Question 4

stem cells

Answer 4

• undifferentiated cells that can continually divide to become specialised

Question 5

four types of stem cells;

Answer 5

• pluripotent
• multipotent
• totipotent
• unipotent

Question 6

totipotent stem cell

Answer 6

can divide into any type of body cell. occur only for limited time in early mammalian embryos

Question 7

pluripotent stem cells

Answer 7

• found in embryos and can become almost any type of cell
• used in research to treat human disorders
• regrow damaged cells like burnt skin cells
• issues as sometimes treatment doesnt work and can continually divide to create tumours
• ethically wrong to make a therapeutic clone of yourself
• destroy embryos

INDUCED PLURIPOTENT;
- take body cell and manipulate the dna by transcription factors

Question 8

multipotent and unipotent stem cells

Answer 8

• found in mature mammals and can divide to form a limited number of different cell types
• multi = such as bone marrow can differentiate into limited number
• uni = differentiate into one type of cell

Question 9

sources of stem cells

Answer 9

• embryos up to 16 days after fertilisation
• umbilical cord blood
• placenta
• adult stem cells such as bone marrow

Question 10

control of gene expression

Answer 10

• gene expression (protein synthesis) is controlled by epigenetics

Question 11

Epigenetics

Answer 11

the heritable change in gene function, without changing the dna base sequencd
- caused by changes in environment and can inhibit transcription
- such as diet, stress and toxins

Question 12

epigenome

Answer 12

• single layer of chemical tags on the SNA
• impacts shape of DNA-histone complex and whether dna is tightly wound so wont be expressed or unwound
• if too tight, transcription factors cant bind

Question 13

Methylation of dna - 1 chemical tag

Answer 13

• increased methylation of dna inhibits transcription
• when methyl groups are added to dna they attach to cyotsine base
• this prevents transcriptional factors from binding
• attracts proteins that condense the dna-histone complex

Question 14

Acetylation of histone proteins - chemical tag

Answer 14

• decreased acetylation of associated histones proteins on dna inhibits transcription
• if acetyl groups are removed from dna, histones become more positive and are attracted more to phopshate group on dna
• makes dna and histones more strongly associated and hard for transcription factors to bind

Question 15

epigenetics and cancer

Answer 15

1. • tumour suppressor genes: produce proteins to slow down cell division and cause cell death if dna copying errors r detected
     - if mutation, cant produce proteins so cell division could continued and mutated cells arent destroyed. BRCA1 and BRCA2 are mutated tumour suppressor genes linked to breast cancer
2. abnormal methylation: control of transcription. methylation can cause a gene to turn on or off. tumour suppressor genes can become hyperethylated,so inactivate and gene turns off. in oncogenes, they may be hypomethylated, reducing methyl groups attached so gene is permanently switched on

Question 16

control of transcription

Answer 16

• transcription stimulated or inhibited when transcriptional factors move from cytoplasm to nucleus
• this turns genes on or off
• only produces certain proteins, cells become specialised
• transcription factor binds to dna it enables rna polymerase to bind so transcription starts
• so mrna sequence is created, translated in cytoplasm to create the protein

Question 17

oestrogen activates transcriptional factor

Answer 17

• steroid hormone (lipid soluble)
• initiates transcription by binding to a receptor site on transcriptional factor
• causes shape change which makes it complementary to bind to DNA, moves into nucleus, rna polymerase can now attach, and initiate transcription
• rna polymerase can only attach once transcription factor

Question 18

regulating translation

Answer 18

• RNA interference inhibits the translation of mRNA produced by target cells
• mRNA molecule that has already been transcribed gets destroyed before translation to create polypeptide chain
• this is done by small interfering RNA (siRNA)

Question 19

how siRNA interferes with translation

Answer 19

• enzyme cuts mRNA into siRNA
• one strand of siRNA combines with another enzyme in cytoplasm
• creates siRNA-enzyme complex, binds via complementary base pairing to another mRNA molecule
• enzyme cuts mRNA so it cant be translated

Question 20

sequencing genome

Answer 20

• methods being used to sequence genomes are continously being improved and updated and has now become automated

Question 21

what can the knowledge of genomes be used for

Answer 21

in simpler organisms:
- prokaryotic cells dont contain introns in dna
- genome can be used directly to sequence the proteins that come from proteome
- useful to identify potential antigens to use in vaccine

in complex organisms;
- have introns and regulatory genes in their dna
- genome cant be used to translate proteome