Chapter 20 - Gene expression Flashcards
What is a mutation?
Change to the structure of quantity of DNA
What is a substitution mutation?
A base is switched for another
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
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
What is an addition mutation?
Base randomly added to sequence
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
What is a base duplication?
One of the bases is repeated
What effect does a duplication mutation have?
Frame shift to the right
What is an inversion mutation?
A group of base sequences becomes separated and rejoins in the inverse order
What is a translocation mutation?
A group of bases becomes separated from the DNA sequence on one chromosome and is inserted into another
What are mutagenic agents?
Increase the frequency and likelihood of mutations
Examples of mutagenic agents
Ionising radiation
Chemicals
Why is ionising radiation a mutagenic agent?
Disrupts DNA structure
Why are chemicals mutagenic agents?
Alters DNA structure and interferes with transcription
What is cell differentiation?
Cell develops into a structure suited to the role it will carry out
How do cells specialise?
Only certain genes are expressed (turned on)
What are totipotent cells?
Can mature into any body cell
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
In which ways does the cell prevent genes from being expressed?
Preventing transcription and translation
What are stem cells?
Can differentiate into other cells
What are embryonic stem cells?
Come from early embryos
Initially, they can differentiate into any type of cell
What are umbilical cord blood stem cells?
Similar to adult stem cells
What are placental stem cells?
Can develop into a limited number of cells
What are adult stem cells?
Specific to tissue or organ
Produce cells to repair and maintain tissues
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
