Topic 3 Flashcards
In which part of an animal cell does aerobic respiration take place?
Mitochondrion
What is the function of a flagellum in a bacterial cell?
To allow motility
Moves the cell
In which part of an animal cell will you find cristae?
Mitochondria
Which part of an animal cell controls what substances enter and leave the cell?
Cell surface membrane
Where does protein synthesis take place in a prokaryotic cell?
Ribosomes
In which part of an animal cell is the majority of the ATP produced?
Mitochondria
Name the fluid inside a mitochondrion
Stroma
Which two animal cell organelles have a double membrane?
Mitochondria
Nucleus
What is found inside a lysosome?
Digestive (hydrolytic) enzymes
Which part of an animal cell helps to form the spindle for cell division?
Centrioles
What is the function of the Golgi Apparatus?
- modify proteins
- sort and package proteins for transport
Where is an animal cell does transcription take place?
Nucleus
Which part of the cell is made of rRNA?
Ribosomes
At which part of a cell does endocytosis take place?
Cell surface membrane
Where in the cell is oxygen used up in a chemical reaction?
Mitochondria
In which 2 parts of an animal cell would you find membranes called cisternae?
ER
Golgi apparatus
In which part of a mucus producing cell would you find the CFTR protein?
Cell surface membrane
Where in a cell does translation take place?
Ribosomes
Does a prokaryotic cell contain cytoplasm?
Yes
Where in an animal cell are chromosomes found?
The nucleus
What is the function of pili in a prokaryotic cell?
Adhesion
What is the only part of an animal cell which is not found in a plant cell?
Centrioles
Which three parts of a plant cell are not found in an animal cell?
- Cellulose cell wall
- chloroplasts
- permanent vacuole
Where exactly in an animal cell does a polypeptide chain fold into a protein?
Lumen of the endoplasmic reticulum
What is the function of the slime layer in a prokaryotic cell?
Prevents dehydration
Where is an animal cell in mRNA produced?
Nucleus
Where in an animal cell are lipids synthesised?
Smooth endoplasmic reticulum
Which part of an animal cell contains hydrolytic enzymes?
Lysosome
Where is the DNA found in a prokaryotic cell?
Cytoplasm
Where are polypeptides made in an animal cell?
Ribosomes
State ways that proteins can be modified in an animal cell
- have a prosthetic group added
Eg carbohydrate
Which is the largest organelle in an animal cell?
Nucleus
Is the DNA in a prokaryotic cell associated with his tone proteins?
No
Are the chromosomes in an animal cell linear or circular?
Linear
Where in an animal cell are tRNA molecules found?
Cytoplasm and ribosomes
What is the difference between ribosomes in a prokaryotic cell and ribosomes in a eukaryotic cell?
Prokaryotic have smaller 70s ribosomes whereas eukaryotic have larger 80s ribosomes
How do proteins move from the rER to the Golgi apparatus?
ER Transport vesicles
By which process do extracellular enzymes leave the cell?
Exocytosis
A nucleus drawn on paper measures 3mm, but its actual size in the cell is 6um. Work out the magnification of the drawing
3000/6 = x500
What is the function of the nucleolus in an animal cell?
The make rRNA for ribosomes
Is the prokaryotic mesosome a part of the cell?
Yes
How many subunits is a ribosome made of?
2
Where is chromatic found?
The nucleus
Name the parts of a nucleus
Nuclear envelope
Nucleoplasm
Nuclear pores
Nucleolus
What is the overall process of making a functional protein?
- gene on DNA
- transcription, mRNA leaves nucleus
- translation
-polypeptide chain released from ribosome and enters rER - protein folded into secondary and tertiary structures as it moves through the lumen
- transport vesicles are produced by rER
- proteins packaged into vesicle
- protein released from cell
Describe the role of the golgi apparatus and rER in the formation of an extracellular enzyme
- amino acids are joined together to form a polypeptide chain on a ribosome attached to the rER
- the polypeptide passes through the cisternae membrane and into the lumen of the rER where the polypeptide folds into its 3d shape
- rER packages proteins into ER vesicles which transport the protein to golgi apparatus
- ER vesicles fuse with golgi apparatus membrane to become part of the golgi apparatus
- protein enters the GA and is modified as protein moves through the GA
- The proteins are packaged into a golgi secretory vesicle for transport through the cell cytoplam
- The vesicle moves to the cell surface membrane, fuses with it and the proteins exit via exocytosis
What cell organelles can be found in a prokaryotic cell?
- cell wall
- capsule
- plasmid
- flagellum
- pili
- ribosome 70s
- mesosomes
- circular DNA
What is a prokaryotic cell wall made of?
peptidoglycan
What is the function of the capsue?
- protection
- prevents dehydration
- prevent enzyme digestion
What does the flagellum allow the cell to be?
motile
- able to move itself
What is the function of pili?
thin protein tubes, may be hollow
- allow for adhesion
- hollow to share plasmids - conjugation
Define ultrastructure
can see using an electron microscope
List the organelles found in an animal cell
- nucleus
- nucleolus
-rER - sER
- ribosomes 80s
- mitochandria
- centrioles
- golgi apparatus
- lysosomes
What cells ae centrioles found in?
only animal cells
What is the DNA in animal cells?
linear, associated with histone proteins
If one cell divides by meiosis, how many daughter cells are made?
4
State the function of the sperm flagellum
to move the sperm to the egg in order for fertilisation. allow for motility
What is the name given to a fertilised egg?
zygote
What is the role of meiosis?
Maintains genetic consistency at fertilisation
produces haploid nuclei for gametes
why does a sperm cell have a larger number of mitochondria than other animal cells?
Sperm cells need a lot of ATP available so that they can swim to the egg for fertilisation
move the flagellum
Does a ovum contain mitochondria?
Yes lots of it
Where would you find an acrosome?
in the head of a sperm
is an ovum diploid or haploid?
haploid
if a dog sperm cell nucleus contains 16 chromosomes, how many chromosomes would be found in a dog nerve cell nucleus?
32
Which part of an animal cell helps to form the spindle for meiosis?
centrioles
What is released from the acrosome?
digestive (hydrolytic) enzymes to break down the zona pellucida
Why does a human ovum need a large amount of cytoplasm?
To have lots of nutrient for embryonic development
energy for cell division
contains lipid droplets
When does the zona pellucida of the ovum thicken?
in the cortical reaction, once a sperm nucleus had fuses with the cell membrane
after one sperm has entered the ovum
why does the ovum need to thicken?
to prevent polyspermy
Does an ovum contain golgi apparatus?
no
Where in a sperm cell are mitochondria found?
in the body/middle peice
Why is it important that a sperm cell is haploid?
to maintain (diploid number ) genetic consistency upon fertilisation
Why does an ovum need to contain lipid droplets?
to provide nutrients for embryonic development/cell division
What is the function of cortical granules?
They contain enzymes which start the cortical reaction
How many chromosomes are present in a human zygote?
23 pairs
46
What are homologous chromosomes?
chromosomes in a pair, have the same locus
Chromosomes with centromere in same position, same length, alleles in same position
In the first division of meiosis, how do the chromosomes line up on the cell equator?
in homologous pairs
What is separated during the second division of meiosis?
sister chromatids
What is a chiasma?
the place where chromosomes cross over
What is independent assortment of chromosomes?
chromosome pair line up randomly along the equator
Describe crossing over
genes on one chromosome swap with the gene at the same locus on another chromosome
State the ways that genetic variation can arise in meiosis?
- crossing over
- independent assortment of chromosomes
Which part of a sperm cell contains hydrolytic enzymes?
the acrosome
acrosin
Which part of an ovum makes the lipids that make up the lipid droplets?
the sEr
Name the cell division that produces gametes
meiosis
What is the advantage of an ovum being many times larger than a sperm cell?
larger target
more cytoplasm to contain lipid droplets
What is the advantage of millions of sperm being released during sexual intercourse?
higher chance of survival and therefore fertilisation
Does a human ovum contain 70s or 80s ribosomes?
80s ribosomes
What is the purpose of the acrosome reaction?
to break down the zona pellucida
- allow sperm to penetrate and enter ovum
How does genetic variation arise in fertilisation?
fertilisation is random
What is the purpose of the cortical reaction?
prevent polyspermy
What are released by the ovum to trigger the stat of the acrosome reaction?
chemokines released by follicle cells
By which transport process do hydrolytic enzymes leave a sperm cell?
exocytosis
Which metal ions are involved in the acrosome reaction?
What do cortical granules contain?
enzymes
How many chromosomes are found in a human ovum?
23
What is polyspermy?
when more than one sperm reach and fertilise the egg
State the differences between the structure of a sperm and an ovum
- sperm have flagellum, ovum does not
- ovum has the rest of the cell organelles, sperm only have acrosome, mitochondria, flagellum and nucleus
- and egg has follicle cells and a zona pellucida
explain the importance of fertilisation?
sexual reproduction
return to 46 chromosomes
Describe the process of fertilisation
- sperm reach the ovum, attracted by chemokines from follicle cells
- sperm come into contact with follicle cells which triggers the acrosome reaction
- the acrosome swells, its membrane fuses with the sperm cell membrane
- digestive enzymes (acrosin) int he acrosome is released
- the enzymes digest through the follicle cells
- the enzymes digest the zona pellucida surrounding the ovum
- receptors on the head of the sperm bind to the ovum vell surface membrane. the sperm membrane fuses with the ovum membrane
- the sperm nucleus enters the ovum
- cortical granules fuse with ovu cell membrane and release digestive enzymes by exocytosis
- ths thickens and hardens the zona pellucida the prevent entry of any other sperm(polyspermy)
- the nuclei of ovum and sperm fuse
What are gametes?
highly specialised cells, 1n, sex cells
Define haploid
half the number of chromosome found in a somatic cell
What type of division in meiosis?
Nuclear or reduction
Meiosis creates _________ among offspring
genetic variation
describe the process of meiosis
-before division occurs each chromosome replicates to become a replicated chromosome, made of two sister chromatids that are genetically identical
- crossing over occurs
- homologous replicated chromosome pairs line up (independent assortment of chromosomes) an separate
- chromatid then separate
- gametes are formed
define stem cell
an undifferentiatd cell that can give rise to specialised cells, has no hayflicks limit, capable of self renewal
Define totipotent stem cell
a stem cell that can give rise to all cell types
Which type of stem cells can be taken bone marrow found inside bones?
multipotent
what would be the absolutist ethical view on using embryonic stem cells in research?
stem cells should not be used
Under no circumstances should embryos be used as a source of stem cells for research. No medical advances are worth the moral evil/murder of using embryonic tissue
- or fine in all circumstances
State the risks/problems of injecting stem cells from donor into a human patient
- risk of rejection
- risk of cancer
- can lead to infection
What would the utilitarian ethical view be on using embryonic stem cells in research?
If the benefits of the research outweigh the cost of collecting the embryos
Where in a blastocyst would you find pluripotent stem cells?
the inner cell mass
Can a pluripotent stem cell give rise to embryonic stem cells?
no
what happens to some genes in a stem cell for it to become specialised?
they become active or inactive
- switched on or off
Where do the embryos come from that are used in stem cell research?
IVF clinics, donors
State some medical uses of stem cells.
- repair tissue
- replace cells
- make new organs/tissue
- cure diseases
define pluripotent stem cell
a stem cell that can give rise to most types of cell
what is unusual about the limits of division for stem cells?
there are none
Does an 8 cell embryo contain totipotent or pluripotent stem cells?
totipotent
What are the problems when trying to extract multipotent stem cells from the body?
they are hard and painful to access
difficult to locate and extract without causing damage
explain how stem cells can be used to produce new skin tissue for a skin graft
skin stem cells are grown on a agar dish until a large enough tissue has been made
- Spare IVF embryos grown to form blastocyst, pluripotent stem cells extracted from inner cell mass, stem cells cultured in the lab to form more identical cells/ tissue/an organ
what are the problems with traditional transplants? How are these problems overcome?
- the is a risk of rejection and therefore immunosuppressants must be taken for the rest of the patients life
If an IVF embryo is used to create new nerve tissue, what problem will arise when this is placed in another persons body?
the body may reject it as this is not their DNA
- shortage of organs
Can a pluripotent stem cell give rise to extra embryonic stem cells?
no
Can a totipotent stem cell give rise to extra embryonic stem cells?
yes
Why is producing skin tissue for a skin graft better done using therapeutic cloning rather than using an IVF embryo?
therapeutic cloning will result in a skin graft containing the same DNA as the patient so wont be rejected
Why are embryonic stem cells more useful then adult multipotent stem cells?
they can give rise to more cell types
Why is it important that stem cell regulatory authorities listen to both scientists and patients when deciding whether embryonic stem cells should be used for research into Parkinson’s disease?
To be ethical
- Scientists involved in embryo research - fully understand the science / recognise what is possible
People not involved in embryo research - give a {balanced /alternative e.g. religious /wider} view eg. patients living with the disease could describe the effects/suffering
Outline the role of the regulatory authorities in making decisions about stem cell research
HFEA
- decide on max age of embryo allowed for research, set or consider ethical aspects /judge what is acceptable, check that source of stem cells is acceptable, prevent cloning (of humans), stop unnecessary repeating of research
What are the uses of stem cells in medical therapies?
- inject into bod to give rise to specialised cell types in order to replace dead/damaged cells and repair damaged tissue
– produce tissues or organs for transplant - treat a wide range of diseases caused by faulty or damaged cells
- used in drug testing and research
What is the process of therapeutic cloning?
- nucleus of egg cell removed
- nucleus from chosen diploid somatic cell is placed in the egg cell
- using electric stimulus the cell divides by mitosis to produce a blastocyst
- pluripotent cells are removed and encouraged to develop into tissue/organs
What does HFEA stand for?
Human Fertilisation and Embryology Authority
What are the roles of the HFEA?
- decide maximum age of an embryo allowed to n=be used for research
- consider ethical issues
- check that the source of stem cells is acceptable
- stop human cloning
- stop unnecessary repeating of research
- to ensure research institutions have a licence
What are the disadvantages of iPS?
- difficult to create
- difficult to control differentiation, may lead to cancer
what can a plant tissue culture be used for?
- improve plant and crop species
- produce increased quantities of plant chemical found in drugs
- produce commercial plants that are difficult to grow from seed , orchids
- conserve endangered plant species
describe the process of a plant tissue culture
- explants are placed on an agar medium with nutrients and growth regulators
- cell divides to form a callus, mass of undifferentiated cells
- callus is made to differentiate into small groups of cells (plant embryos) by growth regulators
- embryos develop into complete plants that are genetically identical
If one cell divides by mitosis, how many daughter cells are made?
2
State the processes of prophase
- chromosomes condense
- centrioles move to opposite poles of the cell
- the spindle forms, ready to attach to the chromosomes
- the nucleolus and nuclear envelope breaks down
State the importance of mitosis
- maintains genetic consistency by creating diploid nuclei
- allows for growth of multicellular organisms and repair
- increase cell number
- asexual reproduction, produce genetically identical cells
Explain the differences between cytokinesis in an animal cell compared to a plant cell
Animal cell splits using the contraction of a ring protein filaments to constrict cell membrane
- plants forms a cell plate down the middle of the cell
Does mitosis produce genetically identical cells?
yes
State the role of the chromosome centromere in mitosis
this is where the spindle fibres attach in order to pull the chromatids apart
Explain the role of the spindle in mitosis
to pull apart the chromatids to opposite poles of the cell, attaches to chromosomes via centromeres
Name the four stages of mitosis in order
- Prophase, prepare
- Metaphase, meet
- Anaphase, apart
- Telophase, two
PMAT
Which part of an animal cell helps to form the spindle for mitosis?
centrioles
In which stage of mitosis do the chromosomes line up along the equator of the cell?
Metaphase
Explain what happens in anaphase of mitosis
- spindle attaches to centromere
- spindle shortens, pulling chromatids to opposite poles of the cell
In which stage of the cell cycle does DNA replication take place?
in interphase, S phase
In which stage of the cell cycle do cells not have visible chromosomes?
interphase
wat divides in cytokinesis?
the cytoplasm
What are the stages of the cell cycle in order?
- interphase
-Growth 1
-S phase
-Growth 2 - mitosis
-prophase
-metaphase
-anaphase
-telophase - cytokinesis
In which stage of mitosis do the chromatids separate?
anaphase
How would you recognisee a cell in telophase of mitosis?
- there are two nuclei
Wat happens to the DNA content of a cell during S phase of the cell cycle? Why?
it doubles as the DNA is replicated, when cell divides the diploid number with be maintained
Is the nuclear envelope present in anaphase of mitosis?
no
In which stage of mitosis do chromosomes condense?
prophase
How exactly do spindle fibres pull chromatids apart?
By shortening and contracting
when a chromosome lines up on the equator in mitosis, are its two chromatids identical or different?
identical
What happens in the G1 phase of interphase?
The cell grows larger and new organelles are made. Enzymes for DNA replication are made
How many nuclei reform in a cell in telophase of mitosis?
2
name an organism which reproduces asexually by mitosis
plants
-Bacteria (by fission), yeast (by budding), fungi (by spores), some plants eg. strawberry plants (by vegetative propagation), annelids (by fragmentation)
During which stage of mitosis do spindle fibres shorten?
anaphase
During which stage of mitosis do chromosomes start to uncoil?
Telophase
What happens in the G2 phase of the cell cycle?
cell organelles double
-Cell growth, protein synthesis to make spindle proteins, chromosomes start to condense
explain how to calculate the miotic index
Add up the total number of cells that are in prophase, metaphase, anaphase and telophase (so in mitosis) – any cell with visible chromosomes, so don’t include any cells in interphase
Divide this number by the total number of cells that can be seen
Where in a plant root cell would cells be actively dividing by mitosis?
meristem
If a cell is not in mitosis what stage of the cell cycle must it be in?
interphase
name the type of cell division involved when a zygote divides into 2 cells?
mitosis
How many divisions of mitosis must take place before a cell can be taken from an embryo for preimplantation genetic diagnosis?
3 as 8 cell embryo needed, one cell is removed and screened
One cell went through many cycles of division by mitosis. when 128 cells have been produced, how many divisions have taken place?
7
Which two stages of mitosis require a spindle?
- anaphase
- metaphase
describe what happens in mataphase
- chromosomes attach to spindle fibres by their centromere
- line up along the equator of the cell
describe the process of telophase
- chromosomes unravel
- nuclear envelope forms around each group of chromosomes
- two nucleolus’ reform
- spindle fibres break down
How do the chromosomes condense?
- DNA and histone proteins coil to form chromatin fibre
- chromatin fibre attaches to a protein scaffold, forming loops
- folding the protein scaffold produces the condensed chromosomes
What is used in cytokinesis in animal cells to split the cytoplasm?
- microtubules
- protein filaments
Define mitosis
Nuclear division resulting in 2 identical diploid nuclei produce from one parent diploid nucleus
Define gene expression
When a gene is used to make mRNA and then gene products (usually proteins)
What is needed to trigger differential gene expression?
A chemical stimulus
State another term for ‘switching off’ a gene
inactivation
State another term for ‘switching on’ a gene
activation
Which two molecule must bind to a gene to switch it on?
- transcription factors
- RNA polymerase
Which molecule can bind to a gene to switch it off?
a repressor molecule
Which enzyme is needed for transcription?
RNA polymerase
Which molecule is produced when a gene is transcribed?
mRNA
What type of stimulus is needed to trigger cell specialisation?
a chemical stimulus
Where does RNA polymerase bind to DNA?
the promotor region
What is a transcription factor?
a molecule that must bind to the promotor region in order for RNA polymerase to bind and transcription to happen
State the two places where the protein repressor can bind to keep a gene switched off
- the promotor region
- the transcription factors
State the four things needed for transcription to take place
- transcription factors
- RNA polymerase
- DNA strand
- mRNA mononucleutides
Which DNA strand acts as the template strand fro transcription?
antisense
Which two molecules bind to the promotor region of DNA?
- transcription factor
- RNA polymerase
Experiments with Acetabularia proved that which part of the cell controls development?
the nucleus
If a gene is switched on, which two molecules can then be produced?
mRNA then polypeptide
Can mRNA be made from a gene that is switched off?
no
Why do different cells make different proteins?
They have different genes switched on
Which type of molecule permanently modifies cells so that they become specialised?
Proteins/enzymes
Can mRNA be made from a gen that is switched on?
yes
In which type of organism will you find the ‘lac operon ‘ gene?
prokaryotic
Which molecule acts as a chemical stimulus to switch on the lac operon gene?
lactose
State the name of the enzyme which is made when the lac opern genes are switched on
beta galactosidase
name the two monosaccharides which are released when lactose is hydrolysed
glucose, galactose
Why is it beneficial for bacteria not to make the enzyme whixh breaks down lactose, if lactose is not present?
saves energy and resources
in prokaryotes, what does the repressor bind to, in order to switch a gene off?
the operator gene
in prokaryotes, what binds to the repressor molecule to inactivate it?
the chemical stimulus
What does beta galactosidase enzyme break down?
lactose
What are master genes?
genes that are responsible for the development of body segments
Where in a cell in mRNA translated?
ribosomes (on rER)
Where is a cell does transcription take place?
nucleus
Cells become _______ through _______________________
specialised
differential gen expression
what does the structure and functionn of a cell depend on?
the proteins it has
True or false: all cells contain the complete genome
true, besides RBC, all genes present but only some are activated
Why are cells specialised?
only some genes are switched on/activated and produce mRNA that is translated into proteins
what is the epigenome?
a multitude of chemical compounds that control the production of proteins in particular cells
how do epigenetic markers work?
- DNA methylation- a methyl group attaches to DNA and prevents transcription
- DNA tightly wound around histone proteins prevents access to genes so genes are inactive
- histone modification- epigenetic markers will bind to histone tails and this effects how tightly the DNA is wound, changing which genes are accessible/active or not
Are epigenetic markers copied with the DNA?
yes,
- this ensure that the correct set of genes remain active
Describe gene expression in eukaryotes
- transcription factors bind to the promotor region and act as a sign for RNA polymerase to bind
- RNA polymerase can bind (creating the transcription initiation complex) and start transcribing the DNA to produce mRNA
- the gene is active, proteins can be produced
What are the ways in which a eukaryotic gene can be switched off?
- a protein repressor molecule attaches to the promotor region, blocking attachment site
- a protein repressor molecule attaches to transcription factors, preventing them from binding
Gene expression only occurs if…..
the protein is made
What is the coding region of DNA known as?
the exon, gene
What is the non-coding region f DNA known as?
the intron
Describe gene expression in prokaryotes
a gene will be repressed by a repressor molecule bound to the operator region/gene
- a stimulus e.g. lactose can bind to the repressor molecule and cause it to detach from the DNA
- RNA polymerase can now bind and start transcription of the operon e.g. lac operon
What is an operon?
a set of genes is prokaryotes, the set of protein produced for a particular function
What did Dawid and Sargent’s experiments demonstrate?
different genes are switched on and expressed in different cells- differential gene expression
Is the modification made by proteins produced in a cell permanent?
yes
Define a cell
The basic unit from which living organisms are built. Can be specialised for a particular function
Define tissue
A group of one type of specialised cell which work together to carry out a specific function
Define organ
A group of different tissues which work together to carry out one or more functions
Define organ system
A group of different organs working together for the same function
How do similar specialised cells recognise each other?
Using adhesion molecules
-specific proteins or glycoproteins fond on the cell surface
What do adhesivo molecules allow the cell to do?
They can bind to cells with complementary shapes
Define apoptosis
The programmed cell death
- the process in which healthy animal cells die during the normal development of an organisms
Define master genes
A gene that controls the development of each segment of a body
-produce mRNA that is translated into signal proteins, which switch on the genes responsible for producing the proteins needed to specialise cells
What can a signal molecule also be called?
Ligand
How does the signal from the ligand reach the nucleus?
Through 2nd messenger proteins down the signal transduction pathway
What does the final 2nd messenger proteins do?
Enter the nucleus and turns the inactive transcription factor to the active transcription factor
Name the pigment in skin which causes skin to darken
Melanin
What goes wrong in the cell cycle to cause a tumour to form?
Uncontrolled division, no stopping, no checkpoints
- no brake/halts on cycle, faster/shorter cycle – shorter interphase, uncontrolled cell
division, cells do not specialise,
Name the environmental dietary factors which affect the phenotype of height?
Calcium, protein
State genetic reasons for why people are getting taller
Taller men have more children, less inbreeding
Name the enzyme which produces melanin
Tyrosinase
Which hormone is produced in the brain in response to high UV light?
Melanin stimulating hormone, MSH
Why is the human skin colour considered to be partly due to genotype and partly the environment?
Skin colour is predisposition but will change based on UV exposure
- genotype – skin colour genes inherited based on where ancestors came from
environment – effect of UV light – more melanin made, so skin darker
State and explain environmental reasons why people are getter taller
- better diet
- better health, more calcium for bone growth and protein for muscle growth (diet), better
heating of houses, less child labour
Which amino acid in needed to produce melanin?
Tyrosinase
what is a melansome?
A melanin filled lysosome
- vesicle bounded by a single membrane which contains melanin- made by melanocytes
Does height show continuous or discontinuous variation?
Continuous
What is meant by the term ‘poly genes’?
Genes that code for the same characteristic
- multiple genes at more that one gene locus which interact in the development of a phenotype
How does MSH activate the tyrosinase gene?
binds to MSH receptor on melanosomes, system of messengers may affect the
epigenome – DNA more loosely wrapped around histones, making gene more accessible
for proteins (RNA polymerase and transcription factors) to bind OR DNA not
methylated so RNA polymerase can bind etc.
State environmental factors that can increase the risk of a person developing cancer
- UV
- consumption of carcinogens
- ionising radiation
- asbestos
A mutation in which genes can lead to cancer?
Protooncogenes or tumour suppressor genes
Define ‘mutation’
Change in the base sequence of DNA
Explain how genotype and the environment can both be involved in the development of breast cancer.
Genotype- people can have a genetic predisposition depending on genes inherited
Environment- exposure to environmental factors can increase risk
Define ‘phenotype’
Outward appearance of a characteristic which can be influenced by genotype or both genotype and environment
What happens to human hair colour in high UV light?
It lightens
Which environmental factor affects tyrosinase in Siamese cats?
Temperature
What type of molecule is an MSH receptor?
Likely to be a glycoproteins or glycolipid or protein
Do artic foxes produce more or less MSH receptors in the summer?
Less
Explain why UV light causes hair to lighten
More melanin is produced, but this is destroyed by the high UV light
In summer do Artic foxes produce white or brown fur?
White
What is made in melanocytes?
Melanin
Name the type of receptor found on the cell membrane of melanocytes
MSH receptors
What is unusual about the tyrosinase in Himalayan rabbits and Siamese cats?
Tyrosinase is inhibited by body temperature
Why would a Himalayan rabbit have a white body but black tips on the paws?
Tyrosinase will be inhibited by body temperatures so extremities with a lower temp will be brown/black as melanin is able to be produced
In cancer cells is the cell cycle shorter/faster or longer/slower than normal?
Shorter/faster
Why is cancer more likely to develop in skin than the kidney?
The skin is exposed to UV and more carcinogens, higher rates of mitosis in skin
Define ‘multi factorial disease’
A disease that is dependent in many factors
What does high UV light do the the DNA in unprotected skin nuclei?
Mutate it
What type of cancers are usually cause by exposure to asbestos?
Respiratory cancers
Why is sunscreen similar to melanosomes?
They absorb UV radiation and prevent it mutating the DNA
why is melanin only made from a switched on/activated tyrosinase gene?
Because RNA polymerase is only able to bind to switched on genes
How is the tyrosinase gene switched on?
DNA uncoiled, RNA polymerase binds, regulator protein (transcription factor) binds, no
repressor protein binds
Which enzyme cannot bind to DNA when the tyrosinase gene is switched off?
RNA polymerase
Name the chemical stimulus which causes the tyrosinase gene to be switched on
MSH
Where will melanosomes be found in a skin cell?
Around the nucleus
if a drug trial was comparing a new cancer drug to an existing cancer drug, what would be the best control for the study?
The existing cancer drug
Can tumours develop in plants?
Yes
which molecules need to be able to bind to DNA for a gene to be switched on?
- transcription factors
- RNA polymerase
Define ‘gene expression’
When products are made from a gene
Describe discontinuous variation
- discrete groups with no overlap
- completely determined by genetics
- found at a single locus
Describe continuous variation
- range of phenotypes
- the distribution will be normal in a bell curve
- determined by genetics and environment
- found at different loci
Describe gene linkage
Genes that are inherited together as they are close together on the same chromosome
How will genes be separated and go into different gametes?
When crossing over happens between the two gene loci
Genes are inherited independently if….
- they are on separate chromosomes
- the genes are very far apart on the chromosome
Describe polygenic inheritance
Many genes are involved at more than one locus and each gene has a small effect. The genes interact and the additive effects create more genotypes
Define polygenic inheritance
More than one gene for a single characteristic, with each gene at a different locus. Genes interact with each other, and have additive effects to produce a phenotype. Polygenic inheritance contributes to continuous variation
Define sex-linked genes
An allele or gene responsible for a trait is located on A chromosome
describe DNA methylation
Methylation groups attach to DNA bases and stop the enzyme RNA polymerase binding to DNA. The gene switched off, transcription cannot take place, so no mRNA is formed. No protein is made - gene is not expressed
Describe histone modification
Methyl or acetyl groups attach to histone tail and affect how tightly DNA winds around his tones
- tightly wrapped, gene is inaccessible so is switched off and cannot be transcribed to form mRNA . No protein is formed, the gene is not expressed
- loosely wrapped, gene is accessible so can be transcribed and expressed
Describe oncogenes
These code for proteins which stimulate cycle progression.
Describe tumour suppressor genes
These code from proteins which halt the cell cycle. If mutated the gene may not be expressed to there are no checkpoints in the cell cycle
What is the p53 gene
A tumour suppressor gene that halts the cell cycle at the G1/S checkpoints
