Chapter 20 - Gene Expression Flashcards
What is a mutation
A change to the nucleotide sequence of DNA
How does a mutation occur
It is a spontaneous mistake made during replication of DNA (interphase)
What are the 3 causes of mutations
Base analogs
Radiation
Change DNA bases
What is meant by a substitution mutation
When one base is swapped for another
- Could be no change as DNA is degenerate
- Could cause single amino acid change
What is meant by an addition mutation
When an extra base is added
What is meant by a deletion mutation
A base is removed
- Causes frame shift so all triplets are affected
What is meant by an inversion mutation
A sequence of basis is removed
- Could be no change or could change a few triplets
- Can’t cause frame shift
What is meant by a duplication mutation
When one or more bases are repeated
- Can be more than once
What is meant by a translocation mutation
When a sequence of DNA is moved from one part of genome to another
Why may a mutation cause no change to the amino acid sequence
DNA is degenerate
What is caused if a mutation causes a change to a single amino acid
- Changes one DNA triplet
- Change the translation of one amino acid
- Change the primary structure of the protein
- Change the hydrogen and ionic bonding
- Change in tertiary structure
What is caused if a mutation causes a change to the sequence of amino acids
- Frameshift changes the sequence of all the following DNA triplets
- Changes all the following amino acids in sequence
- Changes the primary structure
- Changes the hydrogen/ionic bonding
- Changes tertiary structure
What are stem cells
Cells that can differentiate to become different types of cells
They can divide for all of the organisms lifetime
What is meant by totipotent stem cells
Cells that have the ability to differentiate into any type of specialised cell
What are examples of totipotent stem cells
Embryonic cells
What is meant by pluripotent stem cells
Cells that can differentiate into many types of specialised cell
Both embryos and adult cells can, but only specialised cells they can’t differentiate into are placental cells
What is meant by multipotent stem cells
Cells that can differentiate into a few types of specialised cells
What is an example of a multipotent stem cell
Bone marrow
Differentiate into red and white blood cells
What is meant by a unipotent stem cell
A cell that can differentiate into one type of specialised cell
What is an example of a unipotent stem cell
Heart unipotent cells that differentiate into cardiomycetes
How can cells differentiate into specialised cells
- All cells contain 100% of an organisms DNA
- Conditions within the cell control which genes are expressed in proteins
- By changing internal environment of the cell, the expression of certain genes is affected
- Cells then become specialised
What are the 3 ways that stem cells can be obtained
- Induced pluripotent stem cells
- Embryonic stem cells
- Adult stem cells
What is an induced pluripotent stem cell (iPS cells)
Treating a unipotent stem cell with transcription factors that make them pluripotent
Explain how iPS cells are obtained
- Modified virus used as a vector
- Virus inserts transcription factor genes from pluripotent cells into the DNA of unipotent stem cells
- Transcription factors are expressed
Explain how embryonic stem cells are obtained
- Embryos are made in a lab by IVF
- Pluripotent stem cells are removed after a few days
- Embryo is destroyed
- Pluripotent stem cells can differentiate with all types of body cells
Explain how adult stem cells are obtained
- Taken from adults during an operation (eg bone marrow)
- Adults stem cells are multipotent so are less useful for medicine as they can’t make every type of cell
Why are stem cells useful for medicine
They can differentiate to form any type of specialised cell, so can be used to replace faulty or damaged cells
What are examples of how stem cells can be used in medicine
- Bone marrow transplant
- Growing new organs
Explain how a bone marrow transplant is useful
- Bone marrow contains multipotent stem cells that can differentiate into white and red blood cells
- If someone’s has faulty bone marrow this can’t be done
- Replace bone marrow from a donor
- Able to produce healthy cells
How can stem cells be used to grow new organs
- iPS cells produced
- iPS organs can be
- Organs have the same antibodies so aren’t rejected
What are the three main advantages of stem cells for medicine
Save lives
Improve quality of life
Prevents suffering
What are some ethical issues with stem cells
- May be taken from IVF embryos which could develop into a foetus if implanted
- A fertilised zygote has a right to life (although unfertilised eggs have been stimulated to prevent this issue)
- Adults stem cells aren’t pluripotent
What is meant by transcription factors
Proteins that control the rate of protein synthesis by switching some genes on and other genes off
What is meant by a promotor region
A short sequence of DNA at the start of a gene (DNA/RNA polymerase attaches to this)
Explain and draw how a transcription factor acts as an activator
- Transcription factor moves from cytoplasm to nucleus
- Binds to promotor region
- Helps RNA polymerase to bind to DNA
- Gene is transcribed
Explain and draw how a transcription factor acts as a repressor
- Transcription factor moves from the cytoplasm into the nucleus
- Binds to promotor region
- Prevent RNA polymerase binding to DNA
- Gene is not transcribed
What is the rate of mitosis controlled by
The expression of tumour suppressor genes and Proto-oncogenes
What is meant by apoptosis
Programmed cell death (basically the opposite to mitosis)
What do tumour suppressor genes do
Make proteins that slow down the rate of mitosis or speed up the rate of apoptosis
Explain how a tumour May develop (tumour suppressor genes)
- Mutation to tumour suppressor Gene
- Proteins May be non-functional
Explain how the protein can be non-functional
- Change to base sequence of gene
- Change to DNA
- Change to triplet codon
- Change to mRNA codon
- Change to amino acid
- Change to primary structure
- Change bonding
- Change tertiary structure
Explain how a tumour May develop (Porto-oncogenes)
- Make proteins that increase the rate of mitosis
- If a Proto-oncogene mutates it is called an oncogene
- Oncogenes can be over expressed
- Increased rate of mitosis
What is meant by epigenetics
Changes to gene expression due to environmental factors (so no change in base sequence of DNA)
How does epigenetic control gene expression
Environmental factors prevent transcription
How is epigenetics useful
It helps organisms respond to changes in their environment
Can be inherited between generations due to control of gene expression
What is an example of epigenetics
Pregnant mice exposed to a famine
Offspring are better adapted to low calories
Explain methylation of DNA
- Methyl can attach to DNA at CpG sites (cytosine and guanine next to each other in DNA)
- Methylated CpG sites prevent transcription enzymes such as RNA polymerase attaching
- Transcription is prevented
More methylation = Terminates transcription
What are histones
Proteins that supercoil DNA into chromatin
Explain acetylation of histones
- Acetyl groups make histones spread out so DNA is less tightly coiled
- Allows transcriptional enzyme to attach
- Gene is expressed
- Enzymes remove acetyl groups
- Preventing transcription
Less acetylation = Terminates transcription
What is RNA interference (RNAi)
Controlling gene expression by preventing translation
Explain what small interfering RNA does (SiRNA)
- Short and double stranded section combines with proteins to form SiRNA-protein complex
- SiRNA becomes single stranded
- SiRNA has complementary base sequence to the target mRNA
- SiRNA-protein complex breaks down mRNA into pieces
- Prevent transcription
- mRNA pieces are recycled
Explain how hypomethylation can cause cancer
- Hypomethylation
- Proto-oncogenes expresses more
- More proteins transcribed
- Uncontrolled cell division causing a tumour
Explain how hypermethylation
- Hypermethylation
- Tumour suppressor genes (less)
- Proteins not transcribed
- Uncontrolled cell division causing a tumour
What are 5 ways that tumour cells can be identified
- More cells dividing (mitosis)
- Nuclei are often large and odd shaped, and there may be more than one per cell
- Cell shape is often irregular
- Loss of normal cell function
- Disorganised cell organelles
What are the 2 types of tumour
Benign
Malignant
Describe benign tumours
- Non cancerous
- Grow slowly
- Harmless
- Can become malignant
Describe malignant tumours
- Cancerous
- Grow quickly
- Harmful (destroy tissues)
- Can spread through blood or lymphatic systems of broken up
Describe the relationship between oestrogen and breast cancer
- High levels of oestrogen can cause some types
- Oestrogen can bind to proteins to form a transcription factor called oestrogen-oestrogen receptor complex
- Increases rate of cell division so increase DNA replication
- Increase chance of mutations and therefore cancer
What is meant by genome
The complete set of genetic material that an organism has (genes and non-coding DNA)
What is meant by proteome
The complete set of proteins that an organism can make
What is meant by phylogeny
Evolutionary relatedness
What are the uses of the genome project
- Understand evolutionary relatedness
- Can help in medicine as it can increase understanding of antigens to develop new vaccines
Explain what MicroRNA does
- MicroRNA combines with a protein
- Forms MicroRNA-protein complex
- Binds to mRNA by complementary base pairing
- Less specific than SiRNA so works on more than one mRNA
- Prevents translation by stopping the ribosome attaching
- mRNA can be stored and used later or recycled
