Chapter 20 - control of gene expression

Question 1

What is a gene

Answer 1

A section of DNA that codes for a polypeptide

Question 2

What is a mutation

Answer 2

Change in nucleotide base sequence of DNA.

Question 3

What is a nucleosome

Answer 3

8 histones with their associated DNA

Question 4

What causes mutations

Answer 4

Mutations are caused randomly by mistakes in DNA replication. Mutations can also be caused by mutagens such as chemical mutagens or radiation

Question 5

Base substitution

Answer 5

one of the nucleotides is swapped with another

Question 6

addition mutation

Answer 6

when a nucleotide is added to the base sequence. Has a greater effect when the addition is at the start of the base sequence

Question 7

deletion mutation

Answer 7

when a nucleotide is deleted from the base sequence. Has a greater effect when the addition is at the start of the base sequence

Question 8

What is a frameshift

Answer 8

when a base deletion or addition occurs the entire base nucleotide base sequence shifts. This is called a frame shift

Question 9

Duplication mutation

Answer 9

When a base or section of the base sequence is duplicated

Question 10

Inversion mutation

Answer 10

Reversal of nucleotide sequence order in a section of the base sequence.

Question 11

Translocation mutation

Answer 11

Movement of DNA segment to a different position in the base sequence.

Question 12

When does a mutation cause a change

Answer 12

Only when the mutation leads to a change in an amino acid that is involved in bonding and that the new amino acid is not similar to the original one.

Question 13

How to mutagenic agents increase the rate of mutations

Answer 13

• They can act as bases
• They can alter bases
• They can alter the structure of DNA

Question 14

Chemical mutagens

Answer 14

Substances like alcohol and benzene causing mutations.

Question 15

Ionising radiation

Answer 15

Radiation like UV and X-rays causing DNA damage.

Question 16

what is genetics

Answer 16

The study of inheritance of the genome

Question 17

what is epigenetics

Answer 17

The process by which heritable changes in gene function are caused by environmental factors. not changes to base sequence.

Question 18

What is the genome

Answer 18

the sum total of all of your genetic instruction

Question 19

What is the epigenome

Answer 19

all of the readable genetic instructions

Question 20

What is the proteome

Answer 20

all of the proteins that a cell can make - what is expressed by the epigenome

Question 21

What is the nucleosome

Answer 21

a group of 8 histone proteins and their DNA

Question 22

Stem cells

Answer 22

Undifferentiated cells capable of division and differentiation.

Question 23

Totipotent stem cells

Answer 23

all of the chromosomes are euchromatins an differentiate into any body. Found in the zygote/early embryonic cells

Question 24

Pluripotent stem cells

Answer 24

Can form any body cell but not embryonic cells. some genes are condensed but most are still open

Question 25

Multipotent stem cells

Answer 25

Limited differentiation but can still be multiple types of cells, e.g., bone marrow cells.

Question 26

Unipotent stem cells

Answer 26

Can differentiate into only one cell type. so can only replicate to form tissues

Question 27

Induced pluripotent stem cells (iPS)

Answer 27

Pluripotent cells created from unipotent stem cells. These cells are altered genetically to acquire characteristics of embryonic stem cells. Made from adult stem cells

Question 28

What is differentiation

Answer 28

the process by which some of the genes of a chromatin become condensed while the rest stay diffuse. This is to ensure that the base sequence of the condensed chromatins is not read by RNA polymerase as the genetic code is not needed

Question 29

What are the characteristics of a condensed chromatin

Answer 29

DNA is methylated Histone proteins are unacetylated stops DNA from being read by RNA polymerase becomes a heterochromatin The DNA coils in on itself

Question 30

What are the characteristics of a diffuse chromatin

Answer 30

DNA is unmethylated Histone proteins are acetylated DNA can be read by RNA polymerase becomes a euchromatin The DNA remains straight

Question 31

Steps in translation

Answer 31

* external factor like oestrogen binds to repressor protein which is blocking the active site of the transcription factor * shape (tertiary structure) of repressor protein changes so it is no longer blocking active site * transcription factor binds to promotor before the start of the gene * transcription factor can read subsequent gene Alternatively the repressor protein could be blocking the promotor instead of the active site of the transcription factor

Question 32

How is transcription regulated

Answer 32

using siRNA (small interfering RNA) * stops translation of mRNA * siRNA gene is transcribed to make siRNA molecule complementary to a specific mRNA (each siRNA molecule is complementary to a specific mRNA molecule) *siRNA associates with a specific restriction endonuclease * siRNA associates with mRNA and cuts it in half *siRNA gene only transcribed when its complementary gene is wrongly transcribed to stop translation of the mRNA

Question 33

how do tumors form

Answer 33

By uncontrolled mitosis of cells. Could be due to mutations in proto-oncogenes or tumor suppressor genes.

Question 34

Oestrogen

Answer 34

Hormone that alters gene transcription processes.

Question 35

Transcription factors

Answer 35

Molecules that initiate transcription by binding DNA.

Question 36

Small interfering RNA (siRNA)

Answer 36

RNA that silences genes by degrading mRNA using the enzyme endonuclease.

Question 37

DNA methylation

Answer 37

Addition of methyl groups suppressing gene transcription.

Question 38

Histone acetylation

Answer 38

Modification affecting DNA accessibility for transcription.

Question 39

Tumour suppressor genes

Answer 39

genes that when transcribed produce proteins that regulate cell division when hypermethylated these cannot be transcribed so no tumor suppressor proteins made

Question 40

Hyper-methylation

Answer 40

Increased methylation affecting gene expression regulation.

Question 41

Malignant tumours

Answer 41

Rapidly growing tumours that spread to other tissues They have irregular shapes, darker nuclei, no adhesion proteins so can move to different locations by metastasis

Question 42

Benign tumours

Answer 42

Slow-growing tumours that do not spread.

Question 43

What does it mean when a molecule is lipid soluble

Answer 43

If a chemical is non polar and small it is lipid soluble meaning it can diffuse through the phospholipid bilayer.