Gene Expression

Question 1

What are the types of gene mutation and how do they change the amino acid sequence

Answer 1

1. Addition- an extra base is inserted which causes a frame shift to the right but not if an addition of 3 or multiple of 3 2. Deletion- a loss of a base which can cause a frame shift to the left so bases read one to the left which leads to different AAs 3. Substitution- a base is replaced, cause cause a stop codon, a different AA or the same AA as degenerate 4. Inversion- group of bases separated from DNA sequence and rejoin in reverse order 5. Duplication- one or more bases are repeated, causes frame shift to right 6. Translocation- group of bases separated from sequence on one chromosome and inserted to another (affects gene expression and abnormal phenotypes)

Question 2

What are the features of the genetic code

Answer 2

Degenerate-several triplets code for the same AA, meaning some mutations have no effect. Non overlapping- one base only used to code for one AA and universal- same triplet codes for same AA in all organisms

Question 3

The causes of gene mutation

Answer 3

Can arise spontaneously during dna replication or increased by mutagenic agents (high energy ionising radiation, chemicals like nitrogen dioxide or benzopyrene in tobacco smoke p)

Question 4

Cell differentiation definition

Answer 4

The process by which cells become specialised for different functions. Specialised cells produce different proteins as different genes are expressed

Question 5

Define to totipotency

Answer 5

A totipotent cell is a single cell that can give rise to a new organism. It is unspecialised and can differentiate into any body cell. Totipotent cells only occur for limited time in early mammalian embryos

Question 6

How do totipotent cells become specialised

Answer 6

During specialisation, only some genes are expressed so only some dna is transcribed and translated (so only certain proteins are made), which results in a specialised cell

Question 7

Example of totipotent cells in plants

Answer 7

Meristems are plant tissue consisting of undifferentiated totipotent cells, which allows plants to regrow parts or form new plants. Plant cells can also de differentiate (become unspecialised) into callus tissue which is totipotent and can then differentiate into specific plant cells using growth factor

Question 8

What are the two features of stem cells

Answer 8

They are unspecialised cells that have: 1. Self renewal- can continuously divide and replicate 2. Potency- can differentiate into specialised cell types

Question 9

What are the types of stem cells and where are they found

Answer 9

1. Totipotent: can differentiate any type of cell and give rise to a new organism, present in zygote and early embryo 2. Pluripotent: can form most cell types, derived from inner cell mass of blastocyst (embryonic and fatal stem cells) 3. Multi potent: can differentiate into a number of closely related cell types (adult stem cells in bone marrow, umbilical cord) 4. Unipotent: differentiate into a single cell type to maintain and repair tissues

Question 10

What are induced pluripotent stem cells / iPS

Answer 10

Unipotent stem cells can be made pluripotent. Body/somatic cells can be genetically altered to make them acquire characteristics of embryonic stem cells as genes previously turned off can be turned on by nuclear reprogramming (overcomes ethical issues of embryonic)

Question 11

How induced pluripotent stem cells can treat disorders

Answer 11

Can be used to regrow tissues that were damaged by accident or disease e.g. myocardium to treat heart disease, B cells of pancreas for type one, nerve cells for Parkinson’s or MS, blood cells for leukaemia and skin cells for burns

Question 12

The difference between protein and AA hormones and steroid hormones (oestrogen)

Answer 12

Protein hormones are hydrophilic so cannot cross the cell surface membrane but bind to receptors to stimulate second messengers and enzymes. Oestrogen is a steroid hormone no os lipid soluble (lipophillic and hydrophobic so can cross the phospholipid bilayer by simple diffusion

Question 13

How does oestrogen affect gene transcription

Answer 13

1.Oestrogen binds to a receptor protein located in the cytoplasm (receptor is complementary to oestrogen) 2. The oestrogen receptor is a transcriptional factor 3. Binding of oestrogen changes the shape of the dna binding site on the transcriptional factor so it can now bind to a specific base sequence of dna 4. Activated transcriptional factor moves into nucleus and bonds to a specific region on dna (the promoter), stimulating the binding of rna polymerase and transcription of mRNA (as in gene expression transcription starts rna polymerase breaks h bonds..)

Question 14

What is small interfering rna siRNA

Answer 14

It is a double stranded rna molecule 20-25 base pairs in length and present in eukaryotes and some prokaryotes. It interferes with gene expression by causing mRNA to break before translation

Question 15

How does small interfering rna affect gene expression

Answer 15

One of the two si rna strands binds to an enzyme and hybridises to its complementary mRNA sequence. The enzyme hydrolyses the targeted mRNA, preventing translation of the associated gene

Question 16

Define epigenetics

Answer 16

heritable changes in gene function that occur without changing the base sequence of DNA.

Question 17

What is the epigenome

Answer 17

refers to the chemical tags on DNA & histones, which affects the packing of chromatin, and therefore the expression of genes.

Question 18

The effect of epigenetic factors on dna and his tones

Answer 18

Loosely-packed chromatin can be easily transcribed. Densely-packed chromatin has low levels of transcription.Histone packing is determined by:the extent of acetylation of histones &
the extent of methylation of DNA

Question 19

Effects of acetylation on his tones and how to remember it

Answer 19

Histone tails have a positive charge and hence associate tightly with the negatively charged DNA. Adding an acetyl group to the tail (acetylation) neutralises the charge, making DNA less tightly coiled and increasing transcription. Decreased acetylation leads to the histones packing more tightly, inhibiting transcription. Remember ahh (a for acetyl group, h for his tones and makes dna relax)

Question 20

Effects of increased methylation on dna

Answer 20

Methylation is the addition of methyl groups to the cytosine bases of DNA. This inhibits the transcription of genes in two ways: 1.Prevents the binding of transcriptional factors to DNA 2.Promotes the condensing of DNA, making it less accessible to transcription factors.

Question 21

Tumour definition (add to any question that talks about tumours)

Answer 21

Tumours are abnormal cell growths resulting from uncontrolled cell division and can occur in any tissue or organ

Question 22

Differences between benign and malignant tumours

Answer 22

Benign: non cancerous, capsulated, non invasive, slow growing, do not metastasise (spread) to other parts of body, cells are normal malignant: cancerous, non capsulated, fast growing, metastasise, cells have large dark nuclei, may be abnormal shape

Question 23

Role of oncogenes and tutor surpressor genes in the development of tumours

Answer 23

Proto-oncogenes code for proteins that stimulate the cell cycle and promote cell growth and proliferation. Tumour suppressor genes code for proteins that repress cell cycle progression and promote apoptosis. Tumours from when suppressor has loss of function and onco has gain of function

Question 24

Effects of methylation of tumour suppressor genes and oncogenes

Answer 24

Hypermethylation (increased methylation) in the promoter region of tumour suppressor gene decreases the expression of the tumour suppressor gene. (Need two copies, one on each chromosome to eliminate suppressor gene) This occurs in the tumour suppressor gene BRCA1, associated with breast cancer. Hypomethylation (reduced methylation) in the promoter region increases the expression of oncogenes.
This can also lead to cancer. (Only one copy of onco gene needed to stem cell proliferation)

Question 25

Explain how increased methylation could lead to cancer (specific marker)

Answer 25

Methyl groups are added to cytosine bases on DNA on both copies of the tumour suppressor gene.
The decreases the transcription of the tumour suppressor gene.
The proteins of this gene slow down mitosis, so fewer proteins will result in an increase in mitosis and cell division, leading to uncontrolled cell growth and cancer.

Question 26

How increased oestrogen levels can cause breast cancer

Answer 26

Fat cells in the breast increase their production of oestrogen after the menopause. Transcription factors activated by oestrogen can bind to genes involved in controlling the cell cycle. (Bind to promoter, stim transcription and binding of rna polymerase)

Question 27

How a competitive inhibitor increases production of mRNA in daughter cells

Answer 27

EGCG binds to the active site of DNMT, decreasing its activity. Therefore there is a decrease in the methylation in the promoter of the tumour suppressor gene.This allows transcription factors to bind to the promoter of the gene. The allows RNA polymerase to bind to the gene and transcribe it, increasing the concentration of mRNA in the daughter cells.

Question 28

What is the genome sequencing project

Answer 28

Genome sequencing projects determine the base sequences that make up the genes of an organism. The loci of these genes on individual chromosomes have also been mapped. The sequence of all the genes of an organism and their chromosome locations has been done for many different species.

Question 29

What is shotgun sequencing and define bioinformatics

Answer 29

Involves researchers cutting dna into small, easily sequenced sections and using computer algorithms to align overlapping segments. Bioinformatics is an interdisciplinary field that uses computer science to sort, store and understand biological data. This information is stored in databases, which use algorithms to collate relevant data for interpretation and analysis.

Question 30

What is the importance of genome sequencing projects

Answer 30

1. Provides information on diseases and predisposition to diseases - this can allow early intervention 2. Can be used to identify the right drugs to use to treat disease (personalised medicine). 3. It is possible to establish evolutionary links between species/ Comparative genomics where the genome sequence of different species is compared

Question 31

Describe the nature of the proteome

Answer 31

The compete set of proteins expressed by an organism./ the assortment of proteins produced at a specific time in a particular cell or tissue type under specified conditions

Question 32

What was the first simple organism to be sequenced and what are the benefits of mapping unicellular organisms

Answer 32

Haemophilus influenza (a bacterium) was the first species to have its genome sequenced (1995). Many unicellular organisms have since been sequenced as part of the Human Microbiome Project. Knowledge of the genomes and proteomes of simple organisms can be used to identify microbes that can be used for making biofuels or cleaning up pollution. data from pathogens can be used to identify potential antigens for use in vaccines.

Question 33

Why is it easier to determine the genome and proteome of simple organisms than complex organisms

Answer 33

1.Prokaryotic organisms have circular DNA without histones 2. Fewer genes 3. Prokaryotic organism do not have introns. For complex organisms, it is not easy to translate base sequence data into amino acid sequences as so much of the genome (98.5%) does not code for proteins.

Question 34

What is a key characteristics of transcriptional factors

Answer 34

The bind to genes

Question 35

When something is phosphorylase, what do you add in the answer

Answer 35

ATP is used to donate phosphate to x

Question 36

Explain how drugs can reverse epigenetic changes that cause cancer

Answer 36

Drugs could increase methylation of onco genes and decrease methylation of tumour suppressor genes. Increased methylation inhibits transcription/expression of genes

Question 37

How do drugs that have similar strictures to oestrogen prevent breast cancer

Answer 37

Drug binds to oestrogen receptor. This prevents bindings of oestrogen so fewer transcriptional factors can bind to the promoter .