20. GENE EXPRESSION Flashcards
What is the single cell produced from fertilisation called?
Zygote
How does a zygote produce more cells to become an embryo and then a foetus?
Mitosis
What causes cells to become differentiated?
Certain genes stay switched on, and certain genes are switched off
Which proteins do the genes that are switched on in a cell code for?
The proteins that are required to carry out the cell’s specialised function
Which proteins do the genes that are switched off in a cell code for?
The proteins that are not required to carry out the cell’s specialised function
Which genes are usually always switched on in most cells?
The genes that code for respiratory enzymes
Define what stem cells are
Stem cells are undifferentiated cells that have the ability to keep dividing
Define what cell potency is
Cell potency is the varying ability of stem cells to differentiate into different specialised cells
What happens to the potency of most cells as they become more specialised?
Cells gradually lose potency as they become more specialised
Name the types of potency a cell can have, from the highest to the lowest potency
Totipotent, Pluripotent, Multipotent and Unipotent
How many types of cells can multipotent cells differentiate into?
Multipotent cells can differentiate into any cell type
Give an example of totipotent stem cells
Embryonic stem cells
How many types of cells can pluripotent cells differentiate into?
Pluripotent cells can differentiate into almost any cell type
Give an example of pluripotent stem cells
Embryonic and foetal stem cells
How many types of cells can multipotent cells differentiate into?
Multipotent cells can differentiate into a limited number of cell types
Give an example of multipotent stem cells
Adult and umbilical stem cell
How many types of cells can unipotent cells differentiate into?
Unipotent cells can only differentiate into one cell type
Give an example of unipotent cell
Differentiated adult somatic cells
Which potency of cell are the only ones that can rise to a whole new organism?
Totipotent (stem) cells
Why are pluripotent stem cells useful for treating certain conditions of organs?
Because they can differentiate into and therefore replace the many different cell types within an organ
Describe the two disadvantages of using pluripotent stem cells to treat conditions of organs
The might differentiate into the wrong cell type, or divide uncontrollably to form a tumour
Which potency of cell are useful for treating conditions caused by non-functioning blood cells?
Multipotent (adult) stem cell
Define what iPS cells are
iPS (induced pluripotent stem) cells are a type of pluripotent stem cell produced from unipotent stem cells
Describe how iPS cells are produced from unipotent cells
Unipotent cells are genetically altered by using transcription factors to switch genes on
How are iPS cells used?
Once iPS cells are formed from a patient’s cell, they are induced to become another type of unipotent cell. This can then be used to treat conditions in the patient.
Why are iPS cells useful in treating conditions?
The new unipotent cell wouldn’t be rejected as it contains the patient’s DNA.
Define what gene expression / gene regulation is
The control of the protein production
Name the two ways gene expression occurs in cells
Transcriptional control, and translational control
How is gene transcription controlled?
Transcriptional factors
Describe the structure of a transcriptional factor
A receptor, which contains the binding site for another molecule. A DNA binding site, which binds to the gene’s promoter.
If a transcriptional factor is switching a gene on, will it be active or inactive before the molecule bind to the receptor site?
Inactive
Describe the effect of the molecule binding to the receptor site
It changes the tertiary shape of the transcriptional factor, making the DNA binding site complementary to the gene promoter
Describe the effect of the DNA binding site of the transcriptional factor binding to the gene promoter
This allows RNA Polymerase to bind to the promoter, initiating transcription and forming mRNA
Name an example of a steroid hormone that binds to a transcriptional factor
Oestrogen
How would a mutation in the gene that coded for the transcription factor reduce the production of a protein?
The mutation would cause a change in the tertiary shape of the transcription factor, making it non-complementary to the gene.
What is siRNA short for?
Short Interfering RNA
What are siRNAs?
Short double-stranded sections of RNA.
How do siRNAs control gene expression?
By initiating the breakdown of mRNA to control translation
siRNAs start as large double-stranded molecules of RNA. How are they processed into siRNAs?
They are cut into smaller siRNAs, which become single stranded
What do siRNAs combine with before they act?
An enzyme
How do siRNAs bind to their target mRNA?
The bases on the siRNA bind to the mRNA by complementary base pairing
How does the siRNA break down the target mRNA?
The enzyme cuts the target mRNA into smaller pieces
How could siRNAs be used to treat cancer?
They could be artificially produced to silence genes that contribute to the growth of tumours
Why do DNA and histones attract each other?
Because DNA is negatively charged, and histones are positively charged
What is chromatin?
The complex that is formed when DNA winds around histones
Name the two types of chromatin
Euchromatin and heterochromatin
How is euchromatin formed?
When the DNA is loosely wound around the histones
If DNA is in the form of euchromatin, what effect will this have on gene expression?
It will increase gene expression, as the genes are easily accessible for transcription because transcription factors can bind
How is heterochromatin formed?
When the DNA is tightly wound around the histones
If DNA is in the form of heterochromatin, what effect will this have on gene expression?
It will decrease gene expression, as the genes are not easily accessible for transcription, because transcription factors cannot bind
What is the epigenome?
A layer of chemical tags attached to the genome
Name the two types of chemical tags in the epigenome
Methyl groups and acetyl groups
Name five factors that can affect the amount of methylation and acetylation of an individual’s epigenome
Diet, stress, toxins, mutagenic agents, carcinogens
Define epigenetics
The heritable changes in gene function, without changes to the base sequence of DNA
Describe how epigenetics occurs by methylation
Methyl groups are added and removed directly to or from the DNA by binding to cytosine
What charge do methyl groups have?
Positive
Describe the effect of increased methylation on chromatin
Increased DNA methlyation causes DNA to wind up tighter (heterochromatin)
Why does increased DNA methylation cause heterochromatin?
Because the positively charged methyl groups are attracted to the negatively charged DNA
Describe the effect of increased methylation on gene expression
Increased methylation decreases gene expression by decreasing transcription
Describe the effect of decreased methylation on chromatin
Decreased DNA methlyation causes DNA winding to loosen (euchromatin)
Why does decreased DNA methylation cause euchromatin?
Because fewer methyl groups means there is less attraction to the negatively charged DNA
Describe the effect of decreased methylation on gene expression
Decreased methylation increases gene expression by increasing transcription
Describe how epigenetics occurs by acetylation
Acetyl groups are added and removed from the histones
What charge do acetyl groups have?
Negative
Describe the effect of decreased acetylation on chromatin
Decreased histone acetylation causes DNA to wind up tighter (heterochromatin)
Why does increased DNA acetylation cause heterochromatin? RECHECK
Fewer acetyl groups causes the histones to become more positive, increasing the attraction between the histones and the DNA
Describe the effect of increased methylation on gene expression RECHECK
Increased acetylation decreases gene expression by decreasing transcription
Describe the effect of increased acetylation on chromatin
Increased histone acetylation causes the winding of DNA around histones to loosen (euchromatin)
Why does increased DNA methylation cause heterochromatin? RECHECK
More acetyl groups causes the histones to become less positive, decreasing the attraction between the histones and the DNA
Describe the effect of increased methylation on gene expression RECHECK
Decreased acetylation increases gene expression by increasing transcription
Define what a tumour is
A mass of undifferentiated cells formed from uncontrolled cell division
What can uncontrolled cell division be caused by?
Mutations
Name the three genes that can lead to tumour formation when mutated
Proto-oncogenes, tumour suppressor genes, and p53 (an example of a tumour suppressor gene)
What are proto-oncogenes?
Genes that code for protein involved in the initiation of DNA replication and mitosis
How can proto-oncogenes become mutated to form oncogenes?
Hypomethylation
What are oncogenes?
Mutated proto-oncogenes that are now permanently switched on
Describe and explain the effect of oncogenes on tumour formation
Transcription occurs continuously, which causes DNA replication, mitosis and therefore cell division to occur continuously.
What are tumour suppressor genes?
They code for proteins involved in slowing down cell division, and causing cell death (apoptosis) if DNA replication errors are detected
How can tumour suppressor genes become mutated?
A gene mutation, or hypermethylation
How do tumour suppressor genes cause tumours if caused by a gene mutation?
The primary amino acid sequence is altered, translating into a non-functioning protein. This causes uncontrolled cell division.
How do tumour suppressor genes cause tumours if caused by hypermethylation?
Transcription is inhibited. This causes unconctrolled cell division.
What is p53?
A protein that stops the cell cycle when the DNA becomes damaged, which prevents mitosis producing more cells with damaged DNA
How do p53 genes become mutated?
Gene mutation
How does the mutated version of p53 cause tumour formation?
Mitosis will continue to occur, producing more cells with faulty DNA. These cells are more likely to become cancerous and undergo uncontrolled cell division.
Name the two types of tumours
Benign and Malignant
What is metastasis?
Spreading to other parts of the body
Describe the growth rate of benign tumours
Slow (but can grow large)
Why are benign tumours not cancerous?
Because they cannot metastasise or invade neighbouring tissues
Explain why benign tumours don’t metastasise
They produce adhesion molecules that stick the tumour cells together, and they are surrounded by a capsule
Why do benign tumours rarely return after surgery?
They are surrounded by a capsule, so total removal is easier.
Describe the growth rate of malignant tumours
Fast (and grow large)
Explain why malignant tumours grow faster
The cells can become unspecialised again (and therefore larger) and the tumour can develop its own blood supply
Why are malignant tumours cancerous?
Because they can metastasise and invade neighbouring tissues
Explain why malignant tumours can metastasise
They do not produce adhesion molecules, and are not surrounded by a capsule
Why are malignant tumours harder to remove by surgery?
Because they do not have a capsule around them, and they can invade neighbouring tissues
Why are malignant tumours more likely to recur after surgery
Because they are more difficult to remove with surgery, and they can metastasise
Why are patients with malignant tumours more likely to require radiotherapy and chemotherapy?
Because malignant tumours are more difficult to remove with surgery, and they can metastasise
Name the two tumour suppressor genes linked to breast cancer
BRCA1 and BRCA2
What are the two main ways breast cancer is caused?
A mutated tumour suppressor gene (BRCA1 or BRCA2) or oestrogen switching on an oncogene
Where is oestrogen produced before and after menopause?
Before menopause, in the ovaries. After menopause, in the fat tissue in the breasts
How does oestrogen switch on oncogenes in the breasts?
It binds to the proto-oncogene, permanently switching it on and forming an oncogene
Define what gene sequencing is
Gene sequencing is determining the nucleotide sequence of genetic material
Name the project that sequenced the human genome over 13 years
The Human Genome Project
Why is the translation of the genome to the proteome complex in eukaryotes?
Because of the presence of non-coding DNA, the epigenome and regulatory genes means not all genes in the genome are translated into proteins in the proteome
Name one application of sequencing genes in pathogens
Sequencing the genes for potential antigens for use in vaccinations
