Level 2 Bio: Epigenetics & Metabolic Pathways Flashcards
Describe what is meant by a ‘metabolic pathway’
A metabolic pathway is a series of enzyme-controlled steps involved in the synthesis or breakdown of a substance. The product of one step becomes the substrate for the next step.
State the end products of the breakdown of phenylalanine
Carbon dioxide (CO₂) & Water (H₂O)
State the end products of the breakdown of tyrosine
Thyroxine or Melanin
Explain how Albinism is caused
Albinism is caused by ‘block 2” where the pigment Melanin which is the end product of Tyrosine is not formed meaning the individual is albino.
Explain how Cretinism is caused
Cretinism is caused by ‘block 3’ where thyroxine the other end product of Tyrosine is not made which results in physical and mental retardation as it is needed to control metabolism.
Name the products that accumulate to cause Alkaptonuria
Homogentisic acid accumulates in the urine and causes connective tissue to turn black and leads to arthritis.
Name the products that accumulate to cause Tyrosinosis
Hydroxyphenolpyruvic acid accumulates in the urine and can cause liver & kidney failure or damage.
Name the products that accumulate to cause Phenylketonuria
Phenylalanine & Phenylpyruvic acid to accumulate, damaging the nervous system, light skin pigmentation, & causes physical and mental retardation.
Explain the term ‘autosomal recessive condition’
Autosomal recessive condition means the mutation has occurred in the gene on an autosome (#15) & not on a sex chromosome & it is recessive as the alleles are recessive.
Describe the relationship between the HEXA gene and hexosaminidase A
The HEXA gene has the base sequence that codes for hexosaminidase A.
Discuss the way DNA controls the function of the cell
DNA contains the genetic information needed to carry out all of the functions & essential processes of the cell.
Discuss the role of enzymes in metabolic pathways
Enzymes control each step of the pathway by catalysation. Therefore metabolic pathways depend on enzymes for the pathway to work.
What is a Metabolic pathway (IMPORTANT)
A metabolic pathway is a series of enzyme catalyzed reactions in which the product of one reaction becomes the substrate for another.
How does Metabolism occur
Metabolism occurs as a series of enzyme-controlled chemical reactions, known as metabolic pathways.
What controls the chemical reactions of metabolism
Specific proteins (enzymes) in the body, control the chemical reactions of metabolism.
What determines what proteins (enzymes) are made in Metabolic pathways
The DNA code
What does a metabolic pathway look like?
Gene A Gene B
↓ ↓
Enzyme A Enzyme B
↓ ↓
Substrate—————>Intermediate————->Product
How does a Metabolic pathway work
A metabolic pathway is when the product of 1 enzyme reaction is the substrate for the next enzyme reaction.
What happens in PKU (Phenylketonuria)
In PKU the body lacks an enzyme called phenylalanine hydroxylase. This means that the body is unable to break down an amino acid called phenylalanine. As a result, levels of phenylalanine build up in the blood & brain.
What happens in Albinism
Albinism is caused by a defect in one of several genes that produce or distribute melanin pigment. The defect also may result in the absence of melanin production or a reduced amount of production. Albinism symptoms are an absence of colour or lighter than normal colour in hair, skin or eyes (light skin pigmentation).
What are needed for each step of a metabolic pathway
Specific enzymes are needed for each step of a metabolic pathway.
What codes for each enzyme in a metabolic pathway?
Each enzyme is coded for by an expressed gene
What can stop an enzyme being made & therefore stop a metabolic pathway
Mutations can stop an enzyme being made & therefore stop a metabolic pathway & this can affect the phenotype of an individual e.g PKU (Phenylketonuria) & Albinism.
What is epigenetics?
Epigenetics is changes in organisms caused by the modification of gene expression (Phenotype) rather than alteration of the genetic code itself.
What 3 things are part of the Nature side of Epigenetics
1) Genetics
2) Physical appearance
3) Biological appearance
What 3 things are part of the Nurture side of Epigenetics
1) Environment
2) Upbringing
3) Social influences
What is the genotype
Genotypes are the genetic makeup of an individual
What is the phenotype
Phenotypes are the set of observable characteristics of an individual resulting from the interaction of it’s genotype with the environment.
What 2 things result in phenotype
Genotype + Environment= Phenotype
What affects the expression of genes?
This is when the environment can affect the expression of genes (Phenotype) even though the genotype remains the same. The phenotype can change due to the influence of temperature, sun, pH, wind e.t.c
What are some examples of when the environment affects the expression of genes
1) Strong winds cause stunted tree growth
2) Acidic soils change the colour of certain flowers
3) Human skin colour depends on the amount of melanin (3 different genes responsible) AND exposure to UV light.
What are some environmental causes of variation
1) What you eat
2) How much exercise you do
3) Your education
4) illness & injury
5) Where you live
As an organism grows and develops what happens (Epigenetics)
As an organism grows and develops, carefully orchestrated chemical reactions activate & deactivate parts of the genome at strategic times & in specific locations.
What is Epigenetics the study of
Epigenetics is the study of these chemical reactions & the factors that influence them.
How does the epigenome respond to the environment
The epigenome dynamically responds to the environment.
What factors regulate gene expression?
Stress, diet, behaviour, toxins & other factors regulate gene expression.
What do the nutrients we extract from food do when they enter metabolic pathways.
The nutrients we extract from food enter metabolic pathways where they are manipulated, modified & molded into molecules the body can use. One such pathway is responsible for making methyl groups.
What are methyl groups
Methyl groups are important epigenetic tags that silence genes.
What can affect the epigenome
Chemicals that enter our bodies can also affect our epigenome
What does the brain do throughout our lives
Throughout our lives, the brain remains flexible & responsive. In addition to receiving signals from the outside world the brain allows us to form memories & learn from our experiences.
What are many functions in the brain accompanied by?
Many brain functions are accompanied at the cellular level by changes in gene expression, which is important for long term storage of information.
When and how does cancer develop
Cancer develops when a cell becomes abnormal & begins to grow out of control. Cancer can begin when a mutation changes a cell’s DNA sequence. But cancer cells also have abnormal epigenomes.
What is cancer being linked to with epigenomes
Cancer is just one of a growing number of diseases that are being linked to abnormalities in the epigenome.
What do cancer cells have a lower level of?
Cancer cells have a lower level of methylation (more active DNA) than healthy cells.
What does too little methylation cause
1) Activation of genes that promote cell growth
2) Chromosome instability
3) Loss of imprinting
What can cancer cells also have
Cancer cells can also have genes that have more methyl (less active) than normal
What do types of genes turned down in cancer cells do
1) Keep cell growth in check
2) Repair damaged DNA
3) Initiate programmed cell death
What do epigenetic tags act as
Epigenetic tags act as a kind of cellular memory, a cells epigenetic profile is the sum of the signals it has received during it’s lifetime.
What do epigenetic tags record?
Epigenetic tags record the cell’s experiences on the DNA, helping to stabilize gene expression. Different experiences cause the epigenetic profiles of each cell type to grow increasingly different overtime. In the end, hundreds of cell types form, each with a distinct identity & a specialized function.
The epigenome changes in response to signals, where do the signals come from?
The epigenome changes in response to signals. Signals come from the outside world (environment).
Early in development where do most signals come from
Early in development most signals come from within cells or neighboring cells.
After birth and as life continues what happens that start to play a role in shaping the epigenome?
After birth and as life continues a wider variety of environmental factors start to play a role in shaping the epigenome.
Even into old age cells continue to listen for signals, what are these two signals?
Even into old age cells continue to listen for signals: Environmental & Internal
Once a signal reaches a cell what happens?
Once a signal reaches a cell, proteins carry information inside to a gene regulatory protein that attaches to a specific sequence of letters on the DNA.
Gene regulatory proteins have 2 functions. What is the first function?
1) They switch specific genes on or off: A gene regulatory protein attaches itself to a specific sequence of DNA on one or more genes. Once there it acts like a switch, activating genes or shutting them down.
What does the first gene regulatory function do once the regulatory protein attaches itself to a specific sequence of DNA on one or more genes?
Once there it acts like a switch, activating genes or shutting them down.
Gene regulatory proteins have 2 functions. What is the second function?
2) It recruits enzymes that add & remove Epigenetic tags: Gene regulatory proteins also recruit enzymes that add or remove Epigenetic tags to the DNA, the histones or both. Epigenetic tags give the cell a way to “remember” what its genes should be doing.
What does the second gene regulatory function do that is similar to the first
It also recruits enzymes that add & remove Epigenetic tags to the DNA, the histones or both.
What do Epigenetic tags do for the cell?
Epigenetic tags give the cell a way to “remember” what its genes should be doing.
As cells grow and divide what happens with the Epigenetic tags?
As cells grow & divide, cellular machinery copies epigenetic tags along with the DNA.
This is important during embryonic development as past experiences inform future choices.
EXTRA INFORMATION:
A cell must first “know” that it’s an eye cell before it decides what part of the eye to become. The epigenomes allows cells to remember their past experiences long after signals fade away.
As cells grow & divide, cellular machinery copies epigenetic tags along with the DNA. Why is this important?
This is important during embryonic development as past experiences inform future choices.
Why is it important during embryonic development that cells grow and divide and cellular machinery copies the epigenetic tags along with the DNA, as past experiences inform future choices?
Because for example a cell must first know it’s an eye cell before it decides what part of the eye to become.
What does the epigenome allow cells to do?
The epigenome allows cells to remember their past experiences long after signals fade away.
Some epigenetic tags remain in place throughout generations. Why?
Some Epigenetic tags remain in place as genetic information passes from one generation to another. A process called epigenetic inheritance.
At certain times during development specialised cellular machinery does what?
At certain times during development specialised cellular machinery scours the genome & erases it’s epigenetic tags, yet some tags make it through & pass from parent to child.
For most genes, we inherit two working copies 1 from mum and 1 from dad. With imprinted genes what happens?
For most genes, we inherit two working copies 1 from mum and 1 from dad. But with imprinted genes we inherit only 1 working copy. Depending on the gene, either the copy from mum or the copy from dad is epigenetically silenced. Silencing usually happens through the addition of methyl groups during egg or sperm formation.
When does silencing usually happen?
Silencing usually happens through the addition of methyl groups during egg or sperm formation.
The epigenetic tags on imprinted genes usually stay put for the life of the organism. But what happens when they are reset?
The epigenetic tags on an imprinted genes usually stay put for the life of the organism. But they reset during egg & sperm formation Regardless of whether they came from mum or dad, certain genes are always silenced in the egg & others are always silenced in the sperm.
Imprinted genes are especially sensitive to environmental signals, why?
Imprinted genes are especially sensitive to environmental signals. Because imprinted genes have only a single active copy & no back-up, any epigenetic changes or “epimutations” will have a greater impact on gene expression.
Environmental signals can also affect the imprinting process itself, how?
Environmental signals can also affect the imprinting process itself. Imprinting happens during egg & sperm formation, when epigenetic tags are added to silence specific genes. Diet, hormones & toxins can all affect this process, impacting the expression of genes in the next generation.
The DNA code determines what _________ (enzymes) are made (IMPORTANT)
The DNA code determines what PROTEINS (enzymes) are made
