topic 3 voice of the genome Flashcards
what is the difference between eukaryotic and prokaryotic cells
eukaryotic cells have a nucleus
prokaryotic cells do not have a nucleus
what are the features of a prokaryotic cell
- 70s ribosome (30s, 50s)
- Pili
- plasmid
- nucleoid
- cell surface memnbrane
- cell wall
- capsle
- cytoplasm
- mesosome
- flagellum
what are pili
thin protein tubes which allow bacteria to stick to the surface of other bacteria. (stick out from cell wall
what is a plasmid
double stranded DNA in a circular structure contain additional genes that aid the bacterium survival
what is a nucleoid
single circular length of DNA folded in a region known as nucleoid
what is the cell wall made of in prokaryotic cells
made of peptidoglycan a polymer of sugar with some amino acids
what is the capsle
slime layer around the cell wall
what are mesosomes
are infoldings in the plasma membrane of the bacterial cell wall.
what are the common features of all cells
DNA, plasma membrane, ribosomes, cytoplasm
what are the features of a eukaryotic cell
- nucleolus
- sER smooth endoplasmic rectilium
- lysosomes
- mitochondria
- 80s ribosomes
- golgi apparatus
- centrioles
- rER rough endoplasmic rectilium
- nucleus
what is sER
smooth endoplasmic rectilium
a series of single tubular sacs made pf membrane
lipids are made here
what are lysosomes
enclosed by single membrane
containing digestive enzymes
destroys organelles and pathogens
what are mitochondria
surrounded by a double membrane envelope
inner membrane in folded into finger like projections called cistae
central area contains a jelly called matrix which contains
70s ribosome DNA
site of respiration
what are 80s ribosome
site of protein synthesis
what is the golgi apparatus
a series of single curved sacs enclosed by a membrane
many vesicles cluster around the golgi apparatus
modifies proteins and packages them in vesicles for transport
what are the centrioles
two hollow cylinders
arranged at right angles to each other
makes the spindle in cell division
what is rER
rough endoplasmic rectilium
series of single, flattend sacs enclosed by a membrane
ribosomes on the surface where proteins are made
what is the nucleus
surrounded by a double membrane envelope
pores in the nuclear envelope
what is the nucleolus
dark staining area within nuclear envelope
region of dense DNA and protein
makes ribosomes
what are the features of a sperm cell
- flagellum
- haploid nucleus
- mid region
- acrosome
what is the flagellum used for in a sperm cell
used for movement to swim
what is the function of the mid region in a sperm cell
mid region contains mitochondria which provide energy from respiration for movement
what is the function of the acrosome in a sperm cell
containing enzymes to digest the outer layers of the egg
what are the features of an egg cell
haploid nucleus cytoplasm special vesicles cortical granules zona pellucide folicle cells
what is the function of the special vesicles in the egg cell
cortical granules
these contain a substance that helps top more than one sperm fertilising the egg
what does the zona pellucide do in the egg cell
jelly layer stops more than one sperm fertilising the egg
name the steps in fertilisation
- the acrosome reaction
- membrane fusion
- cortical reaction
- meiosis is restarted
- fertilisation
what happens in the acrosome reaction
the first step of fertilisation
when the front of the sperm touches the zona pellucida of the egg the acrosome bursts and releases enzymes which digest a channel in the zona pellucida
what happens in membrane fusion
second step of fertilisation
the surface membranes of the sperm and egg fuse together allowing the haploid nucleus from the sperm to enter the cytoplasm of the egg
what happens in the cortical reaction
the third step of fertilisation
vesicles inside the egg called cortical granules fuse with the cell membrane and release their contents. these cause changes in the surface layer of the egg preventing other sperm from entering
when meiosis is restarted in the fertilisation process what happens
the 4th step of fertilisation
the egg is really a secondary ocyte and the presence of the sperm cell causes the 2nd division and meiosis to now occur
what happens in the final stage of fertilisation
the chromosomes from the haploid egg and sperm combine to restore the diploid number
stages in protein trafficking
- 1 transcription of DNA to RNA
- 2 mRNA leaves nucleus to rER ribosomes
- amino acids made into proteins on the ribosomes
- newly made protein stored and folded in rER cavity
- protein being packaged at the ends of the rER membrane closes forming a vesicle
- vesicles pinched off the rER transport protein towards the golgi apparatus
- protein is modified in golgi apparatus
- vesicles pinched off the golgi apparatus contain the modified protein
- vesicles fuse with cell surface membrane releasing protein such as extracellular enzymes
define protein trafficking
the pathway of amino acids from incorporation in protein to secretion from the cell.
define meiosis and what are the aims of meiosis
meiosis is the type of cell division that ends in two daughter cells that are haploid
aims:
- to reduce the number of chromosomes by half to avoid a doubling in each generation. reduction division
- to ensure genetic variation
what happens in before meiosis 1
chromosomes replicate before division after replication each chromosome is made up of two strands of genetic material, two chromatids
what happens in meiosis 1
the homologous chromosomes pair with each other in the middle of the cell.
the homologous chromosomes are pulled apart
two cells are produced with 23 chromosomes each with two chromatids
what happens in meiosis 2
the two products of meiosis 1 divide again
the chromosomes line up along the equator of the cell and the two chromatids are pulled apart.
to give 4 cells each with 23 chromosomes ( 1 chromatid) which become gametes
what are the two sources of genetic variation in meiosis
- independent assortment
2. crossing over of alleles
what happens in independent assortment
meiosis 1
the chromosomes move to either side of the cell randomly. leading to variation by separating alleles into different cells.
what happens in the crossing over of alleles
meiosis 1
when the homologous chromosomes are paired at the beginning of meiosis 1 chromosomes swap parts of their chromatids / genes leading to variation
what is a locus
is the name given ti the particlar location of a gene on a chromosome
what are linked genes
if two genes at the same loci are on the same chromosomes they are linked
if two genes are on the the sex chromosomes they are
sex linked
what are the stages in the cell cycle
interphase (G1 – S —G2)
mitosis
cytokinesis
what are the 3 stages in interphase
- G1
- S
- G2
what happens in interphase
the cell grows
protein synthesis
new organelles are made
towards the end, chromosomes are replicated
what happens in interphase G1
G1
when growth and protein synthesis occur
what happens in interphase S
synthesis of DNA
the events of DNA replication occur
what happens in interphase G2
when further growth and protein synthesis occur
what are the stages in mitosis
prophase
metaphase
anaphase
telophase
what happens in the 1st stage of mitosis
prophase
chromosomes become visable as they condense,
the membrane of the nucleus breaks down
the nucleolous disappears
the centrioles move to either end of the cell and start to produce spindle
what happens in the 2nd stage of mitosis
metaphase
the 46 chromosomes, each consisting of two chromatids line up at the equator
the chromosomes centromeres (the thing joining the two chromatids) attach to spindle fibres at the equator
what happens in the 3rd stage of mitosis
anaphase
spindle fibres contract pulling the chromatids apart
the spindle fibres shorten pulling the two halves of each centromere in opposite direction. one chromatid of each chromosome is pulled to each of the poles.
spindle breaks down
what happens in the 4th stage of mitosis
telophase
chromosomes decondense and become invisible
membrane of nucleus and nucleolus reform.
what happens in cytokinesis
the cytoplasm divides to form 2 new cells
the cell surface membrane constricts around the centre of the cell.
mitosis ensures genetic consistency it does this by
DNA replication prior to nuclear division
the arrangement of the chromosome on the spindle and the separation of chromatids to the poles
why is mitosis so important
- growth
- repair
- a sexual reproduction
what is a sexual reproduction
is the way a organsism reproduces
simple microbes binary fusion.
seen in plants. also in lizards and greenfly
method for observing mitosis for growth
- root tops are placed in ethanoic ethanol to preserve the structures of the cell
- cut 2-3mm peice from the tip because this is where the dividing cells are located
- place this in concentrated HCl to macerate the tissue
- the tip is placed on a slide and ethanoic orcein is added to stain the DNA
- the coverslip is added and pressed firmly to seperate the cells from each other
what are stem cells
undifferentiated cells that keep dividing and so can give rise to other types of cells.
stem cells that can divide to make all other cell types are called what
totipotent stem cells
stem cells that can divide to make only some cell types are called
pluripotent stem cells
stem cells that give rise to the smallest amount of cell types are called
multipotent stem cells
an embryo that coinsist of 8 identical cells these cells are
totipotent
when an embryp is the size of a blastocyst about 50 cells
these cells are pluripotent
how many cell types are there
there are 216 cell types
adult stem cells are usually
mutipotent
what can stem cells possible be used to treat
- parkinsons disease
- miltiple sclerosis
- type 1 diabetes
- burns
what is parkinsons disease
a progressive loss of nerve cells in the brain that are involved in muscle control
what is multiple sclerosis MS
the electrical insulating layer surrounding the nerve cells breaks down.
what are the ethical concerns with using embryonic stem cells
- when does an embryo become a human with rights
should there be a max age for an embryo to be used for research
is it acceptable to use human embryos specially created for research
is it acceptable to fuse an adult human cell with an egg cell to create new stem cells
what is therapeutic cloning
a big problem with transplanting organs is the rejection by the immune system.
however if the organ is grown from the persons own cells here would not be a problem.
somatic cell nuclear transfer:
- a diploid cell is removed from a patient
- the cell’s nucleus is fused with the ovum who’s nucleus has been removed.
- the stem cells arising from this can be encouraged to become whatever tissue is needed.
somatic cells
normal cell not a stem cell.
regulatory authorities
make the decisions about what can be researched and what can’t as well as what can be used in research/
what does the UK law acknowledge as legal uses of embryonic stem cells in research
- to promote avances in the treatment of infertility
- to increase knowledge about the causes of congenital disease
- to increase knowledge about the causes of miscarriage
- to develop more effective methods of contraception
- to develop methods for detecting gene or chromosome abnormalities inn embryos before implantation
what does the structure and function of the cell depend on
protein synthesises
what is the epigenome
controls what genes are expressed leading to different cell types
histone proteins
DNA is wrapped around histone proteins.
modifications to the histone effects how tightly the DNA is wrapped changes whether RNA polymerase can attach and the gene expressed.
what makes up the epigenome
histone proteins and chemcial markers which attach to DNA
how does the epigenome turn off genes (2 ways)
- methylation to the DNA preventing RNA polymerase from binding. preventing transcription.
- modifications to the histone effects how tightly DNA is wrapped around. tightly wrapped DNA means the gene cannot be transcribed
dawid and sargents experiment
- extracted mRNA from undifferentiated and differentiated frog cells.
- complementary DNA (cDNA) strands were produced from all the mRNA in the differentiated cells using enzyme reverse transcriptase which makes DNA from mRNA
- cDNA strands mixed with the undifferentiated cell mRNA complementary strands of cDNA and mRNA combined to produce double stranded hybrids
-when hybrids were separated out remaining cDNA strands that had not been hybridised remained..
this means the two cells were expressing only some of the same genes
what is the lac operon model
prokaryote escherichia coli.
only produce the enzyme beta- galactosidase to break down carbohydrate lactose when present in surroundings converts disaccharide lactose to monosaccharides glucose and galactose
when lactose is not present a lactose repressor molecule bonds to the DNA to prevent transcription of beta-glaactosidase gene.
RNA polymerase cannot bind to the DNA promoter region.
when lactose is present it binds to the repressor preventing it from binding to the DNA and the gene is transcribed
the lac operon model applied to eukaryotes
genes in uncoiled accessible regions of DNA can be transcribed.
RNA polymerase binds to DNA adjacent to the gene to be transcribed the promoter region
only when the enzyme is attached will transcription proceed
the gene remains switched off until enzyme attaches to the promoter region.
the attachment of a regulatory protein is also required.
transcription can be stooped by protein repressor molecules attaching to the DNA of the promoter region.
protein repressor can attach to regulatory proteins also
how are cells organised into tissues
specialised cells group together in clusters
- cells have specific recognition proteins also known as adhesion molecules on their cell surface membrane.
- adhesion molecules help cells to recognise other cells like themselves and stick to them
- the exposed section binds to complementary proteins in adjacent cells particular recognition determine which cell it can attach to.
define cell
specialsed for a particular function
tissue
group of cells work together to carry out one function
organ
a group of tissues that work together to carry out one function
organ system
a group of organs working together to carry out a particular function.
what are epigentic changes controlled by
singles inside and out side of the cell
when DNA replicates what happens to the epigenome
it also replicates ensuring the same expression of genes from daughter cells
what are master genes
control development.
master gene produce mRNA that is translated into signal proteins which switch on genes responsible for producing the proteins needed for specialisation of cells
what happens when a plants start to flower
cells in the meristem become specialised to form organs that make up the flower
what is the ABC model of flowering plants
most hermaphrodite flowers have both male and female structures. containing 4 sets of floral organs: sepals and petals. male stamens and female carpels.
the expression of genes across the meristem determines which structures will form where.
3 genes determine which type of specialised organ will be produced in each area :
A only expressed = sepal
A + B expressed = petal
B + C expressed = stamen
C only expressed = carpel
as with master genes, these gene produce mRNA that code for single proteins that switch on appropriate genes. synthesis of proteins coded for by these genes result in development of specialised cell in each floral organ.
what is polygenetic inheritance
when one or more gene is involved in the inheritance of characteristics
multifactoral conditions are caused by
both genetics and environmental factors
height is controlled by what factors
gnenes and the environment
why has the population gotten taller ( 6 possible reasons)
- taller men have more children. gradual change in genetic make up
- greater movement of people –> less interbreeding
- better nutrition
- improved health
- end of child labour more energy to grow
- better heating, quality clothing reducing energy for body heat
what causes dark pigmented skin
melanin.
made by melanocyte cells found in skin and root of hair.
activated by melanocyte- stimulating hormone (MSH)
receptors for MSH on surface of melanocyte cells
melanocytes place melanin into melanosome organeles which transfer to nearby skin cells and collect around the nucleus, protecting DNA from harmful UV light.
what happens to skin colour when UV light increases
MSH and MSH receptrors making melanocytes are more active causing skin to darken. hair lightens as uv causes chemical and physical changes to melanin and other proteins
animals that have dark spots of hair e.g Himalayan guinea pigs
to make melanin animals use enzynme tyrosinase.
this catalyses the first step in chemical pathways
changing tyrosine into melanin. they have mutant alleles for tryosinase making enzyme unstable and inactive at normal body temperature. bits wear the body is cooler the enzyme remains active. nose, ears, feet.
epigentics and agoti mice
brown mice - agouti gene is methylated and not expressed
yellow obese mice - gene is unmethylated and is expressed. agouti protein binds to the MSH receptors in skin preventing production of dark pigement. also binds to receptors in the part of the brain relating to feeding beahviour.
if the yellow mouse is pregnant and feeds on methyl rich diet her offspring will be slim and brown,
bisphenol A is a compound prevents methylation of agouti gene resulting in yellow obese offspring. but the effect can be avoided by a methyl rich diet.
behaviour effecting epigenetics
offspring of bad grooming motheres brought up with good mothers turned into calm adults.
offspring of good mothers brought up by bad mothers were anxious adults .
the GR gene of pups with low grooming was swiched off due to methylation.
this gene produces a receptor protein that boinds to stress hormone glucocorticoid. it stops the stress response by causing calming singnals to be sent out.
low levels of GR protein, hormone remains higher pups are stressed for longer
what is cancer caused by
damage to DNA. by physical or chemical factors in the environment. UV light, asbestos, carcinogens.
abnormal methylation of genes in cancer cells lead to activation or deactivation of genes controlling cell cycle
oncogenes
code for proteins that stimulate transition to next stage . less methylation leads to cell cycle being continually active causing excessive cell division.
tumour suppressor genes
produce suppresor proteins that stop the cell cycle. DNA mutations or epigentic changes. methylation inactivating these genes and causing no break in the cell cycle loss of control of the cell cycle leads to non stop growth and tumours.
for cancer to occur there needs to be damage to
multiple parts of the cell control system
what does the tumour suppressor gene p53 do
stops the cell cycle by inhibiting enzyme at the G1 / S transition. preventing cell form coping DNA.
lack of p53 means cells cannot stop entry into S phase
how is cancer inherited
gene defects predispose people to cancer
how do mutations predispose a person to breast cancer
mutations in gene BRCA1 predisposes a person to breast cancer. the functioning gene produces a protein used to repair DNA. may get breast cancer if the other allele becomes damaged in breast tissue cells.
environmental risks that increase risk of cancer
- UV physically damages DNA in skin cells.
- Diet linked. plenty of fruit and veg provide antioxidants that destroy radicals which damage DNA
- virus infections triggers. Virus RNA may contain oncogene pocked up from previous host that gets transferred to the persons cells
