Chapter 20 - Gene Expression Flashcards by KJ Hall

What is a mutation?

Change to the structure of quantity of DNA

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What is a substitution mutation?

A base is switched for another

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What are the three possibilities that can occur as the result of a substitution mutation?

A stop codon can be formed - the production of the polypeptide would be stopped
A non-functional protein is formed
No change

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Why can deletion mutations be bad?

If they occur near the start of a polypeptide chain, all following codons will experience a frame shift = non-functional protein produced

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What is an addition mutation?

Base randomly added to sequence

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Why can addition mutations be bad?

If they occur near the start of a polypeptide chain, all following codons will experience a frame shift = non-functional protein produced

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What is a base duplication?

One of the bases is repeated

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What effect does a duplication mutation have?

Frame shift to the right

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What is an inversion mutation?

A group of base sequences becomes separated and rejoins in the inverse order

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What is a translocation mutation?

A group of bases becomes separated from the DNA sequence on one chromosome and is inserted into another

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What are mutagenic agents?

Increase the frequency and likelihood of mutations

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Examples of mutagenic agents

Ionising radiation

Chemicals

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Why is ionising radiation a mutagenic agent?

Disrupts DNA structure

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Why are chemicals mutagenic agents?

Alters DNA structure and interferes with transcription

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What is cell differentiation?

Cell develops into a structure suited to the role it will carry out

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How do cells specialise?

Only certain genes are expressed (turned on)

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What are totipotent cells?

Can mature into any body cell

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How are only some of the genes in a cell expressed?

Only part of the DNA in a cell is made into proteins needed to carry out a specialised function

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In which ways does the cell prevent genes from being expressed?

Preventing transcription and translation

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What are stem cells?

Can differentiate into other cells

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What are embryonic stem cells?

Come from early embryos

Initially, they can differentiate into any type of cell

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What are umbilical cord blood stem cells?

Similar to adult stem cells

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What are placental stem cells?

Can develop into a limited number of cells

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What are adult stem cells?

Specific to tissue or organ

Produce cells to repair and maintain tissues

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What are totipotent stem cells?

Found in early embryo, can differentiate into any cell

What are pluripotent stem cells?

Found in embryos, can differentiate into ALMOST any cell

Example of totipotent cells

Zygote

Example of pluripotent cells

Embryonic/fetal stem cells

What are multipotent stem cells?

Found in adults, can develop into limited number of cells

Examples of multipoint stem cells

Adult stem cells

What are unipotent stem cells?

Only differentiate into one cell, derived from multipotent stem cells

Examples of unipotent stem cells

Cardiomyocytes

How can pluripotent stem cells be used to treat disease?

Cells can be used to regrow damaged tissue (e.g. heart attack, osteoarthritis, type 1 diabetes)

How are induced pluripotent stem cells made?

Unipotent cells make body cells Body cells altered in lab so they take on characteristics of embryonic stem cells These are pluripotent stem cells

What are transcriptional factors?

Molecules that activate genes

Process of controlling gene expression by controlling transcription:

Transcriptional factors move from cytoplasm to nucleus TF binds to specific base sequence of DNA Initiates transcription mRNA and polypeptides produced

How can oestrogen activate a gene?

Diffuses through phospholipid bilayer into cytoplasm Binds to complementary receptor molecule on transcriptional factor Activates DNA binding site on TF by changing its shape TF enters nucleus and binds with complementary DNA Transcription is stimulated

What is epigenetics?

Provides explanations as to how environmental influences alter the genetic inheritance of offspring

What is the epigenome?

Chemical tags surrounding DNA and histones

What do epigenomes do?

Determine the shape of the DNA-histone complex

What is epigenetic silencing?

Keeps genes in tightly coiled environment so can't be read

Why are epigenomes influenced by environment?

They are flexible - change shape so genes are inactivated and activated

What is the genome?

All the genetic material in an organism

What technique is used to sequence DNA?

Whole-Genome Shotgun sequencing

What is Whole-Genome Shotgun sequencing?

Dividing DNA into smaller sections and then using algorithms to overlap repeating sequences to discover the genome

What is the proteome?

The range of proteins the body can produce

Why is it relatively easy to determine the proteome of prokaryotic organisms?

They have just one plasmid of DNA which isn't associated with proteins No introns

What is cancer?

A disease characterised by the uncontrollable growth of cells

What are the two types of tumour?

Benign and malignant

Which type of tumour can grow to a large size?

Both

Which type of tumour grows quickly?

Malignant

Which type of tumour has a normal looking nucleus?

Benign

Which type of tumour has cells that are well differentiated?

Benign

Which type of tumour lacks adhesion molecules?

Malignant

Which type of tumours surrounded by tissue?

Benign

Which type of tumour is more often life threatening?

Malignant

Which type of tumour often affects the whole body?

Malignant

Which type of tumour can normally be removed by surgery?

Benign

Which type of tumour frequently reoccurs after treatment?

Malignant

What are the two main genes involved in cancer?

Oncogenes and tumour suppressor genes

What are oncogenes?

Mutations of proto-oncogenes

What do proto-oncogenes do?

Stimulate a cell to divide when growth molecules attach to its cell membrane

What are the two reasons that a mutated proto-oncogene can be permanently activated?

The oncogene codes for growth factor = cell division | Receptor protein permanently activated

What do tumour suppressor genes do?

Limit cell division

Why does a woman's likelihood of developing breast cancer increase after menopause?

Increased levels of oestrogen

How can oestrogen cause breast cancer?

Binds to a gene that controls cell division and growth Activates gene Uncontrollable cell division occurs

Which gene, when mutated, leads to breast cancer?

BRCA1

How can hypomethylation lead to the formation of tumours?

Occurs in oncogenes and activates them

Describe the process by which hypermethylation of a tumour suppressor gene leads to cancer:

Hypermethylation occurs in promoter region of TSG TSG inactivated Transcription of promoter regions of TSG inhibited TSG inactivated Uncontrollable cell division = cancer

When will DNA be accessible by transcription factors?

The association of histones with DNA is weak so the two are loosely packed

What happens when DNA is accessed by transcription factors?

Creates mRNA which can activate gene

What impact does condensation have on transcription?

Inhibits it - inaccessible by transcription factors

What are the two processes that can lead to condensation?

Decreased acylation of histones or increased methylation of DNA

What is acylation?

Acyl group transferred to molecule

What molecule accepts the acyl group during acylation?

Acetyl coenzyme A

How does decreased acylation inactivate a gene?

Increased +ve charge on histones Increased attraction between histones and phosphate group of DNA Transcription factors can't access DNA

What is methylation?

Adding a methyl group to a molecule

Which base normally accepts the methyl group?

Cytosine

What are the two ways in which methylation inhibits transcription?

Prevents transcriptional factors binding to DNA | Attracts proteins to cause condensation of complex

How does siRNA block gene expression?

An enzyme cuts RNA into smaller siRNA One of the siRNA molecules combines with an enzyme The siRNA guides the enzyme to a mRNA molecule by complementary base pairing When in position, the enzyme cuts the mRNA into smaller chunks The mRNA no longer forms a polypeptide when translated The gene has been blocked

What is siRNA?

Small interfering RNA