UNIT 3 - D 2.2 - Gene Expression Flashcards
What is the term gene expression used to describe?
the process of reading a gene and building a protein that will then be used by the organism
What does gene expression rely on?
transcription and translation
What determines our phenotype?
the types of proteins our cells build
What is an organism’s phenotype?
the set of characteristics that results when the genetic information received from the parents is expressed
What are some examples of phenotypical characteristics?
blood type, eye colour, the ability to develop freckles, the ability to digest lactose
What are phenotypical characteristics the result of?
genes being expressed, transcribed, and translated, and then the protein produced functioning in a particular way
What is the promoter region?
a sequence of DNA found upstream from/ in front of the gene that indicates the gene’s starting point
What does the promoter region help control?
transcription
What is RNA polymerase?
the enzyme in charge of transcription
What does the RNA polymerase attach to along with transcription factors?
the promoter region
What are transcription factors?
proteins that bind to the promoter regions and help regulate DNA’s transcription
What is an example of transcription factors?
promoter proteins
What do promoter proteins do?
encourage the RNA polymerase to attach to the DNA and start transcription
When is the mRNA able to leave the nucleus and be translated into a protein?
after transcription is started, the RNA polymerase can then move along the gene to make an mRNA copy and detach at the end of the gene
When is the enzyme lactase needed?
only when we consume milk or milk-based products
Where are enhancer regions found?
upstream from the gene/before the genetic sequence being transcribed
What does the enhancer region do?
allows certain activator proteins to attach to it and encourage transcription
When is the RNA polymerase allowed to start transcription?
when the transcription factors are connected to both the enhancer region and the promoter region
What would happen if the factor called the repressor was attached to the DNA region called the silencer region?
transcription would be blocked like an off switch
What is an effective way of regulating transcription and, therefore, translation?
switching on and off RNA polymerase’s ability to do its job
What cannot occur is no mRNA is produced?
translation
What is another way of regulating transcription?
breaking up the mRNA that is being used to produce a protein
What is mRNA degredation?
rendering an mRNA molecule useless through breaking up the mRNA being used to create a protein
What does the cell need to do if it needs to stop producing a certain protein?
it needs to stop making new mRNA molecules and destroy the ones already circulating inside the cell
What are at the two ends of mRNA?
at one end, there is a protective cap, at the other there is a tail
What does the cap and tail do on mRNA molecules?
protect it
What is the tail end of an mRNA molecule protected by?
a long sequence of adenine nucleotides
What is the long sequence of adenine nucleotides making up the tail of mRNA called?
the poly A
Why is it important that transcription and translation happens in a certain direction?
so that the order of amino acids in the resulting protein is correct
What direction does the RNA polymerase translate mRNA?
from the cap end towards the tail end
What are exonucleases?
a special type of enzyme
What do exonucleases have to ability to do?
chop up RNA molecules by removing nucleotides one by one from their extremities
What is the decapping complex and its function?
a group of enzymes which can remove the cap of mRNA
What is the deadenylase complex and its function?
a group of enzymes that can remove the adenine nucleotides in the poly A tail of mRNA
Why is it sometimes necessary to remove the caps and tails of mRNA?
the exonucleases that digest mRNA molecules have trouble attaching to the mRNA when their caps and tails are still intact
Why is RNA degradation another way protein synthesis can be regulated by a cell?
becasue once the mRNA has been broken up, it can’t be used for translation anymore
What is epigenesis?
the process that results in the formation of organs and specialized tissue from a single stem cell
What are the three layers of cells in a human embryo?
the ectoderm, the mesoderm, and the endoderm
What does the ectoderm layer form?
tissues such as the skin and brain
What does the mesoderm layer form?
tissues such as the skeleton and circulatory system
What does the endoderm layer form?
tissues such as the lungs and liver
What does the process involved in epigenetics do?
changes the penotype of the cell without changing the genotype
What is an example of external factors which can generate epigenetic phenotypes?
environmental stressors
What is an example of internal factors which can generate epigenetic phenotypes?
signals from molecules present inside the body
What is DNA methylation?
the process by which a methyl group (-CH3) is added to a DNA nucleotide
What does the methyl group act as?
epigenetic tags
What do the methyl groups acting as epigenetic flags do?
they flag part of the genome
What makes a gene inaccessible to RNA polymerase?
methylation of DNA in the promoter region of the gene
What is transcriptional silencing?
the gene not being able to be expressed due to the fact that the gene will not be transcribed due to RNA polymerase not being able to reach the gene due to methylation of the gene in the promoter region
Which embryonic stem cells have not yet differentiated and its DNA has not yet been methylated and can become any category of cells?
totipotent cells
When does methylation become widespread?
as soon as differentiation starts
What contains the patterns of methylation that make each cell specialized for a certain task?
copies of DNA as an embryo grows
What do cells become with further methylation and specialization?
the different kinds of cells, ex. skin, muscle, blood vessels, nerves…
What are exceptions of cells in the human body contining a full copy of the person’s genome?
red blood cells (no nucleus), and gametes (only contain half of genetic material)
What is the genome?
all the genetic information that an organism received from its parents
Which genes do cells express?
the ones needed to perform their specific function
What is the transcriptome?
all the RNA that a cell makes
What are RNA transcripts?
transcribed strands of RNA
Why would biologists want to measure the number of different RNA transcripts and the relative quantities produced?
To learn more about how cells differentiate
What is hoped to be better understood through studying transcriptomes of cells?
embryo development and cancer
What is RNA sequencing?
a technique used to identify RNA transcripts
What is the proteome?
all the proteins that a cell, tissue or organism can produce
What could knowing a person’s proteome lead to?
personalized medicine
Where does methylation often take place?
in the promoter region of DNA
What does the RNA polymerase use to start transcription?
the promoter region
What are methyl groups considered?
epigenetic tags that work like switches to turn transcription on or off
What do long chains of nucleosomes form?
chromatin
What forms a chromosome?
coiled up chromatin
What do the proteins in nucleosomes have to form histone tails?
amino acid sequences
Where does the amino acid lysine exist in more than one position?
along the tail of a histone called histone 3 or H3
What determines whether the methylated lysine activates or silences gene expression?
where it is found
When would the methylated lysine allow for transcription?
if it is towards the tip of the histone tail
When would the methylated lysine silence the gene?
if it si along the tail
What letter is used to label lysine?
K
What does silencing a gene using histone methylation involve?
making loops of DNA coil more tightly around the histones so they are more compressed against each other and not accessible
What does activating a gene involve?
loosening the loops of DNA to seperate the histones from each other and make the DNA available for transcription
Why are epigenetics useful for a population?
because it allows it to adapt its gene expression to different situations
What does epigenetics allow a genome to do?
be applied in different ways in different situations by turning some genes on and others off
Why are researches so interested in epigenetics?
because it can help us understand health issues related to ageing, obesity, addiction, depression, cancer
What does some epigenetics being passed on to the next generation mean for offspring?
some of the experiences the parents or grandparents had could influence which genes are being activated/silenced in the offspring
What can result in epigenetics being passed down to offspring?
certain behaviors and susceptibility to certain diseases
What can researchers do potentially making epigenetic modifications reversable?
remove the silencing methylation on genes they want to turn back on
What can affect epigenetic tags?
where we live and chemicals we are exposed to in our environment
What type of air pollutants are linked to health risks?
ground-level ozone (O3), nitrogen oxides (NOx), particulate matter (PM), polycyclic aromatic hydrocarbons (PAHs)
What have studies shown that methylation patterns in genes of children depend on?
whether the mother was exposed to high or low levels of PAHs in the air
What do females living closer to roads/exposed to more air pollutants have compared to females living further away from major roads?
different methylation patterns in the DNA responsible for the formation of the placenta
When would babies of females have a lower body mass on average?
if the mother was exposed to higher air pollution levels
Why should pregnant women be more careful of what they consume and expose themselves to?
because embryonic cells and cells of developing foetuses are more susceptible to modifications than cells later in life
What do sperm cells and egg cells come from?
primordial germ cells (PGCs)
Where are PGCs formed?
inside an individual when they are a developing foetus
How are epigenetic tags removed on PGCs?
by a process of epigenetic reprogramming
What happens to some of the DNA in sex cells before they mature into egg/sperm cells?
it is remethylated so they can produce a viable zygote
What are imprinted genes?
genes that have been silenced in only one of the two copies, either paternal copy or maternal copy of the gene
What process do imprinted genes bypass?
the epigenetic reprogramming process
Why will an embryo not form, even if there was sufficient genetic material, by combining the nuclei from two egg cells or two sperm cells?
because the genes in the egg and sperm are imprinted differently, they will be methylated one way in the male copy of the gene and a different way in the female copy
What does it mean to have one parent copy of the gene silenced using methylation?
the remaining copy is what determines the phenotype outcome in the offspring
What produces a tigon?
a female lion and male tiger
What produces a liger?
a male lion and a female tiger
What makes a liger grow to an enormous size?
the genes from the father that affect growth are switched on
What are heterozygotic twins?
non-identical twins
When are heterozygotic twins formed?
when two separate eggs are fertalized at the same time by different sperm cells
What are monozygotic twins?
identical twins
How are monozygotic twins formed?
one zygote forms two embryos
What are differentially methylated regions (DMRs)
areas along DNA sequences that researchers study to find out why people with the same genome can have different phenotypes
What does looking for DMRs allow researchers to find out?
whether disease is connected to differences in epigenetics
What needs to happen for insulin to do its job?
the gene for insulin needs to be actively transcribed and translated into insulin when blood sugar levels are high
What triggers the transcription of the insulin gene INS?
the presence of glucose in the blood
What does escherichia coli bacteria do when lactose is present?
they produce the enzyme lactase
How is the production of lactase in E coli turned off?
a zone of DNA upstream from the gene but downstream from the promoter acts as a binding site for lac repressor. As long as the lac repressor is stuck to this sequence of DNA, it acts as a roadblock and stops the RNA polymerase from latching on and transcribing the genetic code
What is the DNA sequence where the lac repressor binds to called?
the operator
How is the production of lactase in E coli turned on?
when the lactose arrives, it binds to the lac repressor and deactivates is so that it detaches from the operator and allows the RNA polymerase to transcribe the genetic code
What makes up the lac operon?
the promoter region, operator, and the gene sequences along the DNA
