20 Gene Expression

Question 1

How to build a complete map of all genetic material in organism

Answer 1

Map dna base sequences that make up genes and map these genes on individual chromosomes of that organism

Question 2

Bioinformatics

Answer 2

Science of collecting and analysing complex biological data such as genetic codes.
uses computers to read, store, and organise biological data at fast rate.
Also uses algorithms to analyse and interpret biological data

Question 3

Whole genome shotgun more detail

Answer 3

Researchers cut DNA into many small easily sequenced sections and use algorithms to align overlapping segments to assemble entire genome

Question 4

What are snps

Answer 4

Single base variations in genome that are associated with disease and other disorders.

Question 5

Importance of sequencing of DNA

Answer 5

Medical screening has allowed quick identification of potential medical problems and early intervention to treat them.
Made is possible also to establish the evolutionary links between species

Question 6

What is a proteome

Answer 6

All proteins produced in a given type of cell ( cellular proteome) or organism (complete proteome) at a given time under specific conditions

Question 7

Human microbiome project

Answer 7

Genomes of thousands of prokaryotic and single celled eukaryotic organisms being sequenced, will provide info to cure diseases and knowledge of genes that can usefully exploited, eg ones from organisms that can withstand extreme or toxic environments.

Question 8

Determining proteome if prokaryotic organisms is relatively easy because

Answer 8

Vast majority of prokaryotes have just one circular piece of DNA that is not associated with histones.
There are none of non coding portions of DNA which are typical of eukaryotic cells.

Question 9

Knowledge of proteome of organisms like bacteria is useful because:

Answer 9

Identification of those proteins that act as antigens on surfaces of human pathogens.
Antigens can be used in vaccines against disease caused by these pathogens, in response to antigen memory cells are produced which trigger a secondary response when antigen encountered on second occasion.

Question 10

Why is it difficult to translate knowledge of genome into proteome

Answer 10

Genome contains many non coding genes as well as others that have a role in regulating other genes.
Also a question of whose DNA is used for mapping

Question 11

Substitution of bases, three consequences

Answer 11

Formation of one of three stop codons which mark end of polypeptide chain, polypeptide production stopped prematurely and final protein may be unable to perform normal function.
Formation of codon for different amino acid, structure of polypeptide produced would differ in a single amino acid, protein may change.
Formation of different codon which produces same codon for same amino acid, no effect on polypeptide produced.

Question 12

Deletion of bases causes

Answer 12

Frame shift, most triplets will be different as will amino acids they code for and polypeptides.

Question 13

Basic mutation rate can be increased by outside factors known as

Answer 13

Mutagenic agents.

Question 14

Effect of high energy ionising radiation and chemicals

Answer 14

Radiation can disrupt structure of DNA.

Chemicals can interfere with transcription.

Question 15

Why are all cells capable of producing everything

Answer 15

All cells in organism derived by mitotic divisions of fertilised egg (zygote). They all contain exactly the same genes. So all cells capable of making everything body can produce

Question 16

Why don’t all cells produce insulin then?

Answer 16

Although all cells contain all genes only certain genes are expressed (switched on) in any one cell at any one time.
Some are permanently expressed e.g. genes that code for enzymes involved in respiration, transcription, translation, ribosomes and tRNA synthesis. Others are permanently switched off and some are switched on and off when needed.

Question 17

Totipotent cells

Answer 17

Cells such as fertilised eggs can mature into any body cell. The early cells derived from fertilised egg are also totipotent. These later differentiate and become specialised.
Totipotent stem cells are found in early embryo and can differentiate into any type of cells, zygote is totipotent. Zygote cells become more specialised and become pluripotent stem cells.

Question 18

Why do cells not all produce all proteins the body can produce

Answer 18

During process of cell specialisation on,y some of genes are expressed, so only part of DNA of cell is translated into proteins.
This is to conserve energy and resources. Variety of stimuli ensure genes for other proteins are not expressed.

Question 19

How are genes prevented from expressing themselves

Answer 19

Preventing transcription and so preventing the production of mRNA.
Preventing translation.

Question 20

If specialised cells retain all genes can they develop into any other cell?

Answer 20

It depends. Some cells such as xylem are so specialised that they lose nuclei once they are mature. As nucleus contains genes then these cannot develop into other cells. Once cells have specialised they can no longer develop into other cells. In mature mammals only a few cells retain the ability to differentiate into other cells (stem cells)

Question 21

Self renewal

Answer 21

Stem cells are undifferentiated dividing cells that occur in adult animal tissues and have ability of divide into identical copy of themselves.

Question 22

Embryonic stem cells

Answer 22

Come from embryos in early stages of development, can differentiate into any type of cell in initial stages of development.

Question 23

Umbilical cord blood stem cells

Answer 23

Derived from umbilical cord blood and are similar to adult stem cells

Question 24

Placental stem cells

Answer 24

Found in placenta and develop into specific types of cells

Question 25

Adult stem cells

Answer 25

Found in body tissues of foetus through to adult. They are specific to particular tissues of organ within which they produce cells to maintain and repair tissue.

Question 26

Types of stem cells

Answer 26

Totipotent.
Pluripotent.
Multipotent.
Unipotent.

Question 27

Example of pluripotent stem cells

Answer 27

Embryonic stem cells and fetal stem cells

Question 28

Examples of multipotent stem cells

Answer 28

Adult stem cells and umbilical cord blood stem cells

Question 29

Induced pluripotent stem cells

Answer 29

Type of pluripotent cell, produces from unipotent stem cells. Can be almost any body cells, these are genetically altered in lab to make them acquire characteristics of embryonic stem cells. To do this involves inducing genes and transcriptional factors (turn on genes).
This shows adult cells retain same genetic info that was present in embryo.
They are not exactly same as embryonic stem cells. They can potentially divide indefinitely to provide limitless supply, could be used medically without ethical concerns e.g. regrow damaged tissue

Question 30

Potential uses of human cells produced by stem cells

Answer 30

SEE PAGE 507

Question 31

In vivo culturing of human embryonic stem cells

Answer 31

SEE PAGE 508

Question 32

Effect of oestrogen on gene transcription

Answer 32

For transcription to begin, gene is switched on by specific molecules called transcriptional factors, that move from cytoplasm into nucleus.
Each transcriptional factor has a site that binds to a specific base sequence of the DNA in the nucleus.
When it binds, it causes region of DNA to begin transcription.
mRNA is produced and info it carried is translated into a polypeptide.
When a gene is not being expressed (switched off) the site on the transcriptional factor that binds to DNA is not active.
As site on transcriptional factor binding to DNA is inactive it cannot cause transcription and polypeptide synthesis
SEE PAGE 511

Question 33

Which part of cell surface membrane does oestrogen diffuse through

Answer 33

Phospholipid portion of cell surface membrane

Question 34

What does oestrogen bind to

Answer 34

Site on receptor molecule of transcriptional factor.

The transcriptional factor can enter the nucleus and bind to specific base sequence on DNA

Question 35

Epigenetics

Answer 35

Environmental factors can cause heritable changes in gene function without changing the base sequence of DNA.
Environmental influences can subtly alter the genetic inheritance of an organisms offspring.

Question 36

Epigenome

Answer 36

DNA and histones are covered in chemicals sometimes called tags. These chemical tags form a second layer known as epigenome. The epigenome determines the shape of the DNA histone complex eg it can unwrap active greens so that DNA is exposed and can easily be transcribed (switches then on) .
Epigenome of cell is accumulation of signals it has received during its lifetime. In early development signal comes from within cells of foetus and nutrition from mother. Later in life environment and hormones affect epigenome.

Question 37

Why is epigenome flexible

Answer 37

DNA code is fixed by epigenome flexible because chemical tags respond to environmental changes. Factors like diet and stress can cause chemical tags to adjust wrapping and unwrapping of DNA and so switch genes on and off.

Question 38

How does environment affect epigenome

Answer 38

Environmental signal stimulates proteins to carry its message inside cell from where it is passed by a series of other proteins into nucleus. Then message passes to specific protein which can be attached to a specific sequence of bases on DNA. Once attached the protein has two possible effects. It can change:
Acetylation of histones leading to the activation or inhibition of a gene.
Methylation of DNA by attracting enzymes that can add or remove methyl groups.

Question 39

The DNA histone complex

Answer 39

Where association of histones with DNA is weak the DNA histone complex is less condensed (loosely packed). Here the DNA is accessible by transcription factors which can initiate production of mRNA, gene can be switched on. Reverse when association is stronger.
Condensation of DNA histone complex therefore inhibits transcription.

Question 40

Which group donates the acetyl group

Answer 40

Acetylcoenzyme A

Question 41

Decreased acetylation increases attraction to..

Answer 41

Phosphate groups of DNA.

Transcription factors cannot initiate mRNA production from DNA, gene is switched off.

Question 42

Effects of epigentic factors on DNA histone complex

Answer 42

SEE PAGE 515

Question 43

Altering any of epigentic processes can cause

Answer 43

Abnormal activity or silencing of genes. Can cause cancer.
Specific sections of DNA (near promoter regions) have no methylation in normal cells. In cancer cells these regions become highly methylated causing genes that should be active to switch off.

Question 44

What can epigenetic changes affect

Answer 44

They do not alter sequence of bases in DNA but can increase incidence of mutations.
In inherited cancer where there is increased methylation of genes that has led to protective genes being switched off, damaged base sequences in DNA are not repaired leading to cancer.

Question 45

Epigenetic therapy

Answer 45

Use drugs to inhibit certain enzymes involved in either histone acetylation or DNA methylation.
Must be targeted specifically on cancer cells. If drugs affect normal cells they could activate gene transcription and make them cancerous.
Epigentic can all be used in development of diagnostic tests that help detect early stages of cancer, brain disorders etc. They identify level of DNA methylation and histone acetylation.

Question 46

In eukaryotes and prokaryotes translation of mRNA produced by gene can be inhibited by

Answer 46

Breaking mRNA down Benfro it’s coded info can be translated into a polypeptide. One type of small RNA molecule that may be involved: small interfering RNA (siRNA)

Question 47

Mechanism of RNA interference on gene expression

Answer 47

An enzyme cuts large double stranded molecules of RNA into smaller section called small interfering RNA (siRNA).
One of two siRNA strands combined with an enzyme.
siRNA molecules guides enzyme to a messenger RNA molecule by pairing up its bases with complementary ones on a section of mRNA.
Once in position, the enzyme cuts the mRNA into smaller sections.
mRNA no longer capable of being translated into a polypeptide.
This means that the gene has not be expressed, it has been blocked.
SEE PAGE 517

Question 48

Cancer

Answer 48

Group of disease caused by damage to genes that regulate mitosis and cell cycle. Leading to unrestrained growth of cells. Group of abnormal cells called tumour develops and expands in size. Cancer cells are derived from single mutant cell leading to uncontrolled mitosis in cell. Further mutation in one of the descendant cells leads to other changes that cause subsequent cells to be abnormal in growth and appearance.

Question 49

Comparison of benign and malignant tumours

Answer 49

SEE PAGE 519

Question 50

Oncogenes

Answer 50

Photo-oncogenes stimulate a cell to divide when growth factors attach to a protein receptor on its cell surface membrane. This activates genes that cause DNA to replicate and cell to divide. If proto o muatates into oncogene it can become permanently activated for two reasons :
Receptor protein on cell surf.memb can be permanently activated so cell division switched on even in absence of growth factors.
The oncogene may code for a growth factor that is then produced in excess again stimulating excess cell division.

Question 51

Tumour suppressor genes

Answer 51

Slow down cell division and repair mistakes in DNA and induce apoptosis in cells. If this gene becomes mutated it is inactivated so stoked inhibiting cell division and cells can grow out of control. While most of these cells die those that survive can make clones and form tumours. Some cancers are caused by inherited mutations of tumour suppressor genes but more are acquired not inherited.

Question 52

Most common abnormality is…

Answer 52

Hypermethylation

Question 53

Hypermethylation process

Answer 53

Hypermethylation occurs in a specific region (promoter region) of tumour suppressor genes.
This leads to the tumour supressor gene being inactivated.
Transcription of promoter regions of tumour suppressor genes is inhibited.
The tumour suppressor gene is therefore silenced.
As tumour suppressor gene normally slows the rate of cell division it’s inactivation leads to increased cell division and formation of a tumour.
Example: occurs in tumour suppressor gene BRCA1 leading to development of breast cancer

Question 54

Another form of abnormal methylation

Answer 54

Hypomethylation, reduced methylation. Found to occur in oncogene where it leads to their activation and hence formation of tumours

Question 55

When do fat cells of breast produce more oestrogen

Answer 55

After menopause.

White blood cells drawn to the tumour that develops also increase oestrogen production.

Question 56

In general how does oestrogen cause tumour to develop

Answer 56

If gene oestrogen acts on is one that controls cell divisor and growth then it will be activated and it’s continued divisor could produce a tumour. E.g. oestrogen causes proto oncogenes of cells in breast tissue to develop into oncogenes, leading to development of tumour.