1
Q
Using a graticule
A
to measure the size of individual cells or organelles
By using a stage micrometer -a slide with a very accurate scale in micrometres (um)
Can calibrate your graticule for the lens of the microscope => for accuracy
2
Q
Magnification
A
Magnification - how much bigger the image is when compared to the real object
3
Q
Resolution
A
Resolution - how far apart the 2 objects must be before we see them separately
4
Q
Light Microscopes
A
specimen or thin slice of biological material is placed on the stage of a light microscope
-> ensure the sample is as THIN as possible for light to pass through
-> stain to highlight certain structures
is illuminated from underneath, either by sunlight reflected with a mirror or by a built-in light source
objective lens produces a magnified image
eyepiece lens focuses this image at the eye + image is magnified again
5
Q
Total magnification
A
Total magnification = magnification of objective lens x magnification of eyepiece lens
6
Q
Magnification equation
A
Image/ magnification = actual image
7
Q
Stains (iodine/acetocarmine/methylene blue/haematoxylin)
A
The staining is used to make it easier to identify types of cell or parts of cells under the microscope
haematoxylin - stains the nuclei of plant and animal cells purple, and cytoplasm pink
methylene blue - stains the nuclei of animal cells blue
acetocarmine - stains the chromosomes in dividing nuclei in both plant and animal cells
iodine - stains starch-containing material in plant cells blue-black
8
Q
Gram Staining Procedure
A
only for prokaryotic cells
used for antibiotic production => most work by destroying cell walls so the knowledge of type of cell wall is imp
shows that there are 2 types of prokaryotic cell walls
Transferring bacteria (colourless) to a glass slide and fixing it with heat
Bacteria are submerged into crystal-violet iodine complex
Dehydrate with ethanol
Submerge into red safranin counter stain
Wash, dry and view it under the microscope
9
Q
Gram positive bacteria
A
Purple (thick layer of peptidoglycan with loads of teichoic acid => traps crystal violets stain) -> Gram positive bacteria
Cristal Violet trapped within peptidoglycan layer and resist decolorisation when dehydrated with ethanol
Wall doesn’t pick up the red safranin counter stain
Appears blue/purple when viewed under the light microscope
10
Q
Gram negative bacteria
A
Pink (thin layer of peptidoglycan with no teichoic acid - has an outer membrane around cell wall) -> Gram negative bacteria
thin layer of peptidoglycan between 2 membranes
outer membrane (lipopolysaccharide) picks up crystal violet iodine complex
outer membrane dehydrates in ethanol and washes out the stain
now thin peptidoglycan layer is exposed and takes up the red safranin counter stain
appears red when viewed under the light microscope
11
Q
Adv and disadv of light microscope
A
Adv:
- seeing living organisms
- relatively cheap/light/portable
Disadv:
- artefacts
- low resolution and magnification
12
Q
Electron Microscopes
A
preparation of specimen -> very complex process => chemical preservation, freeze-drying, freeze-fracturing, removing the water (dehydration), embedding, sectioning and mounting on a metal grid
-> often stained using heavy metal ions such as lead and uranium => to improve the scattering of the electrons -> more contrast which is clearer and easier to interpret
uses a beam of electrons to form an image
-> electrons are scattered by the specimen similarly how the light is scattered in the light microscope
-> same as light but with a very tiny wavelength => higher resolution + magnification
beam is focused by magnets, not lenses
Image is displayed on a monitor or computer screen
13
Q
TEMs microscope
A
Transmission electron micrographs (TEMs) -> 2D images in B&W similar to those from a light microscope => highest magnification + resolution, samples are in vacuum + set in resin
14
Q
SEMs microscopes
A
Scanning electron microscope (SEMs) -> have a lower magnification than TEM, but images are three-dimensional (3D), produce B&W, samples are in vacuum too
15
Q
Adv and disadv of electron microscopes
A
Adv:
- huge magnification and resolution
Disadv:
- examined in vacuum hence dead specimen
- artefacts
- extremely expensive/ huge
- need specially trained staff/ special high pressure conditions
16
Q
Ultrastructure and Protoplasm
A
Ultrastructure - small structure discovered using electron microscope (including organelles)
Protoplasm - nucleus + cytoplasm => what was seen first in a light microscope
17
Q
Cell Membrane
A
controls movement of substances
localise enzymes in reaction pathways (eg respiration in mitochondria)
keep biological molecules separate (hydrologic enzymes in lysosomes)
18
Q
Nucleus
A
Largest organelle
surrounded by double membrane = nuclear envelope
has nuclear pores
contains DNA which is bonded to the proteinin the form of chromatin when the cell is not dividing and chromosomes when it is => condenses into chromosomes when it is dividing
contains the nucleolus inside itself
19
Q
Nucleolus
A
- darker, denser area
pure DNA and protein in there
produce ribosomes and involved in cell division and growth
20
Q
Ribosomes
A
made of ribosomal RNA and protein
used in protein synthesis to assemble the polypeptide shape
80S (how quickly the particles fall to the bottom of the tube in the centrifuge) ribosome => made of 2 units (large subunit 60S and small subunit 40S)
free in cytoplasm OR attached to the rough ER
PLANTS => another type found in mitochondria and chloroplasts of eukaryotic cells and prokaryotic cells = 70S (large subunit 50S and small subunit 30S)
21
Q
RER
A
3D network of cavities surrounded by membranes
made from flattened scars of membrane called cisternae
have ribosomes (80S) attached onto them => location of extracellular protein synthesis - produce proteins, then they are secreted out of the cell or become attached to the cell surface membrane, pass into the lumen of RER where they are folded and processed
once the protein is made, the membrane can pinch off to form a vesicle and be transported around the cell
RER is usually found next to the nucleus and sometimes joined to the nuclear envelop (continuous with the nuclear envelop => large SA)
22
Q
SER
A
same structure as RER but without ribosomes
separate to RER
to manufacture lipids and steroids such as certain hormones
23
Q
Mitochondria
A
Site of aerobic respiration
produce ATP
capsule shape made from a double membrane filled with fluid called matrix
inner membrane is folded into cristae to provide a large SA
have their own DNA + ribosomes and replicate during cell division (Endosymbiotic Theory - used to be a separate organism)
24
Q
Centrioles
A
Only in animal cell
found near nucleus, usually at right angle to each other
each one is a bundle of nine microtubules
move to the opposite ends and produce the microtubule spindle that will attach to the chromosomes and pull them apart during cell division
25
Lysosomes
Contagion digestive enzymes
in cytoplasm
use for breaking down old organelles and in some organisms food
can fuse with cell membrane and release its enzymes out of the cell (exocytosis)
used in programmed cell death (apoptosis) when the cell self-destructs
26
Golgi Apparatus
=> electron microscope used for showing details of the internal structure of the Golgi apparatus
=> labelling specific enzymes so we can see them using the electron microscope
Inner areas of the Golgi apparatus, nearer to the RER, are very rich in enzymes that modify proteins -> enzymes or membrane proteins are converted into the final product
Outer regions of the Golgi apparatus you find lots of finished protein products,but not many of the enzymes that make them
Golgi apparatus aligns the areas of the protein that need to be on the outside of the cell membrane, such as receptor binding sites => inserted facing in the correct direction
dense area of cytoplasm
made of stacks of parallel, flattened membrane pockets formed by vesicles for ER fusing together
27
Protein synthesis in Golgi Apparatuses
RER releases the vesicle with protein which moves towards Golgi Apparatus
The vesicles fuse with the membrane sacs of the Golgi apparatus and the protein enters the Golgi stacks.
The proteins are modified as they travel through the Golgi apparatus.
Carbohydrate is added to some proteins to form glycoproteins such as mucus involved in producing materials for plant and fungal cell walls and insect cuticles
Lipids are added to proteins to form lipoproteins (transport lipids to plasma in organs)
Some proteins in the Golgi apparatus are digestive enzymes => enclosed in vesicles to form lysosomes OR enzymes may be transported through the Golgi apparatus and then in vesicles to the cell surface membrane to fuse with the membrane to release extracellular digestive enzymes
Delivered to other membrane-bound organelles
LEAVE IT IN VESICLES (BUD OFF) BY EXOCYTOSIS
28
Classifications
Gram positive/negatrive
shape (cocci, bacilli, vibrois, spirilla)
Respiratory requirements (obligate aerobes - need oxygen to survive, facultative anaerobes - use oxygen if available, obligate anaerobes - killed by presence of oxygen)
28
Protein synthesis in Golgi Apparatuses
RER releases the vesicle with protein which moves towards Golgi Apparatus
The vesicles fuse with the membrane sacs of the Golgi apparatus and the protein enters the Golgi stacks.
The proteins are modified as they travel through the Golgi apparatus.
Carbohydrate is added to some proteins to form glycoproteins such as mucus involved in producing materials for plant and fungal cell walls and insect cuticles
Lipids are added to proteins to form lipoproteins (transport lipids to plasma in organs)
Some proteins in the Golgi apparatus are digestive enzymes => enclosed in vesicles to form lysosomes OR enzymes may be transported through the Golgi apparatus and then in vesicles to the cell surface membrane to fuse with the membrane to release extracellular digestive enzymes
Delivered to other membrane-bound organelles
LEAVE IT IN VESICLES (BUD OFF) BY EXOCYTOSIS
29
Prokaryote cells
bacteria
archea
30
Draw an eukaryotic cell
*check*
31
Draw a prokaryotic cell ALWAYS PRESENT
*check*
32
Draw a prokaryotic cell SOMETIMES PRESENT
*check*
33
Prokaryote cells
bacteria
archea
34
Cell Wall
Prevents cell bursting and gives bacteria its shape
Made of peptidoglycan (many parallel polysaccharides chains with short peptide crosss-linkages)
35
Capsule
Only on some bacteria
around cell wall, made of starch, gelatin, protein and glycolipids
covers cell markers on cell membrane making immune detections and phagocytosis difficult
help bacteria survive in very dry conditions
36
Cell surface membrane in prokaryotic cells
Similar to eukaryotic cells
respiratory enzymes are embedded as no mitochondria
37
Mesosomes
Inward folds where the respiratory enzymes are found
same function as mitochondrion
38
Nucleoid
Don’t have a nucleus
DNA in a form of one, long, single strand
free-floating in a cytoplasm
39
Plasmid
Small circular loops of DNA that code for particular bacterial phenotypes (toxins, antibiotic resistance)
Can reproduce independently of the nucleoid
can be transferred from one bacterium to another in a form of sexual reproduction using pili
40
Ribosomes
Smaller than eukaryotic ribosomes (70S = 30S and 50S subunits)
Same functions as in eukaryotic protein synthesis
41
Flagella
Flagella => movement
made from protein fibres (flagellin) which are spun around like a motor
made from many-stranded helix of flagellin protein
42
Pili
Pili => protein projections on outside
attach to host cells
carry out sexual reproduction
can be used by viruses to gain entry to the cell => make bacteria more vulnerable
43
Cell
Cell - smallest building block of organisms
44
Tissue and 4 types of them
Tissue - group of specialised cells working together to perform a specific function(s)
connective
muscle
nervous
epithelial
45
Squamous/cuboidal/columnar tissue
Squamous: line the surface of blood vessels and form capillary walls and alveolar walls
Cuboidal and columnar: line many other tubes in the body
46
Ciliated and glandular tissues
Ciliated and Glandular: often contain mucus producing goblet cells and are found in the bronchioles and oviduct
47
Compound Stratified tissue
Compound stratified: found in places that are continuously abraded such as the skin, the layer is thick and protective as new cells grow from the basement membrane and push cells outwards
48
Organ
Organ - group of several diff types of tissues working together efficiently to perform a specific function(s)
49
Organ system
Organ System - group of organs working together to perform a large scale function(s)
50
Chromosomes
All DNA must duplicate before the cell divides
So that one copy of DNA can go into each one of the 2 daughter cells
before division is in form of chromatin => condenses into chromosomes
46 chromosomes in human
51
Karyotype
Karyotype - a photograph of the chromosomes in a cell
52
Chromosomes formation
-> DNA molecule winds around proteins called histones (positively charged basic protein) to form nucleosome
-> Nucleosome supercoil to form dense chromosome structure
-> these replicate before the cell divides to make a double stranded chromatid
53
Cell cycle phases
different cycling control when each stage of the cycle occurs
cyclins will bind to cyclin-dependent kinases (CDKs)
these cyclin-CDK complexes become active
they cause phosphorylation (attach phosphate groups to proteins) = changes shape
these proteins then become active and carry out functions specific to one of the phases of the cell cycle
unless certain cyclin doesn’t reach a threshold conc, the cell doesn’t progress to the next stage
-> phosphorylation of chromatin = chromatin condenses into chromosomes (dense and coiled)
-> phosphorylation of nuclear envelope = break down of nuclear membrane during cell division
54
Interphase (G1, S, G2)
Interphase => period of non-division - increase in mass and size, 3 stages
G1 (gap 1): longest phase
cell grows and develops
normal cell processes occur
cell will make proteins needed for cell division
ATP produced for cell division
S (synthesis):
Genetic material is copied
Chromosomes replicate and become double stranded chromatid
G2 (gap 2):
Organelles will duplicate
More cytoplasm is produced as the cell grows further
DNA is checked for error
55
Mitosis
Mitosis => active division
asexual reproduction => involves one parent, genetically identical offspring (clone), fast and simple, lack of genetic variation making the entire population to vulnerable to changes in the environment
growth => permanent increase in number, size or mass of cells, development; animals stop at maturity, whilst plants grow throughout their lifespan in meristems (top of the plant)
repair => tissues become damaged and need repairing all the time
56
Mitosis Stages
P - prophase
M - metaphase
A - anaphase
T - telophase
57
Prophase
Centrioles begin to move to the opposite poles of the cells
Nucleolus breaks down followed by the nuclear envelope
Duplicated chromosomes are clearly visible with the 2 sister chromatids joined by a centromere
58
Metaphase
Centrioles will form a spindle which is made from microtubules
Microtubules attach to the centromere of each centromere of each chromatid pair
They push and pull them so they line up along the equator (metaphase plate) of the cells
59
Anaphase
Centromeres split and the sister chromatids become individual again
They are pulled centromere first towards opposite poles
This is done by the microtubules contractions which uses up ATP stored in interphase
60
Telophase
Spindle starts to break down
Nuclear envelopes and nucleoli reform
Chromosomes become less dense
61
Meiosis
Meiosis => gamete production
sexual reproduction => involves 2 parent, genetically different offspring, allows for of genetic variation preventing an the entire population from vulnerability to changes in the environment
62
Difference between mitosis and meiosis
The cell divides twice, not once
You end up with 4 haploid cells not 2 diploid
Chromosomes line up in homologous pairs
Independent assortment happens
Crossing over occurs
63
Prophase I
Centrioles begin to move to the opposite poles of the cells
Nucleolus breaks down followed by the nuclear envelope
Duplicated chromosomes are clearly visible with the 2 sister chromatids joined by a centromere
Homologous chromosomes pair up with each other
Crossing over occurs
64
Homologous Chromosomes
Homologous Chromosomes - two versions of each type of chromosome that are arranged in 23 pairs => this is why a diploid cell is called 2n as it actually has 2 versions of each chromosome
65
Crossing-over
Crossing-over: when homologous chromosomes swap parts of their chromosomes, chiasmata form where the chromosomes break => further genetic variation in alleles
Chromosomes twist
Alleles break off and swap
Recombinant chromosomes are formed
66
Independent Assortment
Independent Assortment - each homologous pair can orient themselves differently => adds to genetic variation
67
Metaphase I
Metaphase I:
Centrioles will form a spindle which is made from microtubules
Microtubules attach to the centromere of each centromere of each chromatid pair
They push and pull them so they line up along the equator (metaphase plate) of the cells in their homologous pairs
68
Anaphase I
Anaphase I:
Each pair of sister chromatids are pulled centromere first towards opposite poles
This is done by the microtubules contractions which uses up ATP stored in interphase
69
Telophase I
Telophase I:
Spindle starts to break down
Nuclear envelopes and nucleoli reform and cell begins to divide
2 haploid cells with 23 double chromatids in each
70
PMAT2
PMAT2 occurs the same way as in mitosis => produces 4 haploid cells
71
Cytokinesis: animal and plant cells
Cytokinesis => separation of new cells
split the cytoplasm between 2 newly made cells
ANIMAL
the plasma membrane is pulled inwards around the equator of the cell to form cleavage furrow
This is done by using a contractile ring of protein made up of actin and myosin fibres
PLANT
a new cell wall is formed across the equator of the cell
a middle lamella forms first, and the cellulose is deposited here by both of the cells on either side to form cell walls
72
Sexual Reproduction
- process involving fusion of the nuclei of 2 sex cells (gametes) to form a zygote and the production of the offsprings that are genetically different from each other (usually 2 parents: half of genetic material comes from both parents)
73
Asexual Reproduction
- process resulting in genetically identical (direct copy - clone) offsprings being produced from 1 parent
74
Adv and Disadv of sexual reproduction
Sexual Reproduction
genetic variation -> natural selection; adaptability; diseases not affecting entire population
takes more time + energy; hard for isolated population to reproduce; limited number of offsprings
75
Adv and disadv of asexual reproduction
Asexual Reproduction
takes less time + energy; large number of offsprings; rapid increase in population (right condition)
no genetic variation -> vulnerability to changes in environment + diseases affecting entire population;
76
Fertilisation
Fertilisation - fusion of the nuclei of the egg cell and sperm cell to form a zygote
-> formed in sex organs (gonads) = gametogenesis by meiosis
77
Acrosome Reaction
During sexual intercourse, semen is ejaculated high up into the vagina of the female, near the cervix
Sperm cells follow a chemical trail released by the egg cell and travel up through the cervix to reach the uterus
Sperm then travels into the oviduct containing the egg cell
If a sperm cell meets the egg cell in the oviduct, fertilisation can occur (1-2 days after ovulation)
During fertilisation, the head of a sperm cell releases enzymes (acrosome fuses with the sperm cell membrane) that digest a path through the protective outer layer of the egg cell (zona pellucida) allowing the sperm cell membrane to fuse with the egg cell membrane => Acrosome reaction
-> acrosomes have been matured since being ejaculated, once the sperm touch the zona pellucida => acrosome reaction is triggered
78
Fertilisation
Fertilisation - fusion of the nuclei of the egg cell and sperm cell to form a zygote
-> formed in sex organs (gonads) = gametogenesis by meiosis
79
Cortical Reaction
Once this has occurred, egg cell immediately releases the contents of vesicles known as cortical granules into the space between the egg cell membrane and the zona pellucida
Chemicals contained within them cause the zona pellucida to rapidly thicken and harden, preventing any more sperm cells from entering, ensuring only one sperm cell can fertilize the egg cell => Cortical reaction
80
Egg Cell adaptations
Zona pellucida = has a jelly like coat that will change after fertilisation
is very large (visible to human eye)
has many mitochondria so it’s ready for cell division after fertilisation
has a haploid nucleus (23 chromosomes)
contains lipid droplets as a source of energy/ mitochondria to release ATP
81
Draw an egg cell
*check*
82
Draw a sperm cell
*check*
83
Sperm Cell adaptations
has a tail (flagellum propels the sperms by its movement) so it can swim from the testes to the oviduct => microtubules produces a whip-like motion
is much smaller than egg
has many mitochondria to give it energy to swim
has special membrane-bound storage site for digestive enzymes called acrosome that help it to break through cell membrane of the egg
has a haploid nucleus (23 chromosomes) = nucleus contains tightly condensed chromosomes (reduces the amount of energy needed to transport it)
84
Plants: sepal/ petal/ stamen/ anther/ stigma/ ovary
Sepal -> protects the unopened flower
Petal -> may be brightly coloured to attract the insects
Stamen -> male parts of the plant, consisting of anther and filament
Anther -> produces the male sex cells (pollen)
Stigma -> the top of the female part of the plant, which collects pollen grains
Ovary -> produces female sex cells (contained in the ovules)
85
Sporophytic generation
Sporophytic generation - diploid and produces spores by mitosis (plant body)
86
Gametophytic
Gametophytic - haploid and produce gamete by mitosis (content of anther and ovary)
87
Microgametogenesis
Male gamete - pollen (produced in the anther of the stamens - each contains roughly four pollen sacs where meiosis occurs to produce haploid nuclei) = microgametogenesis
88
Microgametogenesis: production
You start off with microspore mother cells which are diploid
These divide by meiosis to produce 4 haploid microspores
Then an asymmetric division occurs by mitosis
This results in 2 distinct nuclei: a large tube nucleus and a small generative nucleus
So there are 2 haploid nuclei in the same cell
Pollination needs to occur - pollen grains are transferred from anthers to stigma (self-pollination/ cross-pollination by wind or insect)
Generative nuclei divides once more by mitosis so there are now three nuclei in the pollen grain
89
Megagemetogenesis
Female gamete - ovum (contained within ovules in the ovary - ovule is attached to the wall of the ovary by placenta tissue) = megagametogenesis
90
Megagametogenesis: production
You start off with megaspore mother cells which are diploid
These divide by meiosis to produce 4 haploid megaspores
3 of them die and the last one continues to develop
It develops by dividing by mitosis to make an embryo sac with 8 haploid nuclei
One of the is the egg cell, 3 are antipodal cells, 2 synergid (short lived nuclei that aid the pollen nucleus reaching the egg nucleus, signal guidance) and 2 polar nuclei
91
Pollination: gametes movement
Pollen lands on the stigma
Pollen tube grows due to tube cell nucleus which digests its way through the tissue of the style and into the ovary reaching micropyle of an ovule
Other 2 nuclei go down the pollen tube and enter the ovule
One of the generative nuclei fuses with the egg forming a diploid zygote
Another fuses with the 2 polar nuclei to form a triploid endosperm nucleus - this is used to supply the embryonic plant with food at germination
92
Stem Cells
Stem cells - unspecialised cells that can divide by mitosis an unlimited number of times
Each new cell has a potential to remain a stem cell or to develop into a specialised cell such as => differentiation
93
Potency
Potency - ability of the stem cells to differentiate into more specialised cell types
94
Totipotency
Totipotency – totipotent stem cells are embryonic stem cells that can differentiate into any cell type found in an embryo, as well as extra-embryonic cells (the cells that make up the placenta and umbilical cord)
-> zygote contains totipotent cells (can become any type of cells)
rapid mitosis (cleavage) takes place where the cells divide constantly without interphase between divisions
tiny cells of the embryo are undifferentiated, totipotent and are called embryonic stem cells
after 4 days, there's a solid ball of 10-30 days = morula (still totipotent)
95
Pluripotency
Pluripotency – pluripotent stem cells are embryonic stem cells that can differentiate into any cell type found in an embryo but are not able to differentiate into cells forming the placenta and umbilical cord
After another day, the blastocyst (has an outer layer of cells and an inner mass of cells) is formed made of pluripotent (can only form most other cell types, not extra-embryonic structures like placenta)
Some of their genes have been permanently switched off
96
Multipotency
Multipotency – multipotent stem cells are adult stem cells that have lost some of the potency associated with embryonic stem cells and are no longer pluripotent
as the embryo develops, they become more specialised, becoming multipotent
Eventually they become so specialised they form the same cell type every time they divide, becoming unipotent cells
97
Adult Stem Cells
remain undifferentiated and can be found in tissues and organs amongst highly specialised cells
only a small number of adult cells in tissues
difficult to extract and form a limited range of specialised cells (multipotent)
difficult to grow in the lab
98
How do chromosomes prevent active transcription?
Totipotent-> Pluripotent -> Differentiated Somatic Cells (body cells) achieved by switching on and off transcription of certain genes => in differentiation, some parts of chromosomes coil/uncoil in order to prevent active transcription; as the development of the organism progresses, more genes are silenced (combination of genes that are active and silenced results in the characteristics of the fully differentiated mature cells)
99
Umbilical cord and pluripotent cells
Blood drained from the placenta and umbilical cord, after birth, is a rich source of pluripotent stem cells
If this blood if frozen, it can be available throughout the life of the person, should they need it
It would be spatially demanding and expensive to do it for every newborn, there's very little of cord blood being used to cure people
100
Uses of stem-cell therapy
ability to differentiate into other specialised cell types
potential to replace damaged tissues and cells (that result from certain diseases)
101
Stem Cell Therapy
Treating leukaemia (bone marrow cancer)
existing stem cells in the bone marrow are killed, before being replaced using a bone marrow stem cell transplant
will eventually replace all the bone marrow cells
Promote Tissue Regeneration
Modulate the Immune System
Reduce Inflammation
Improve Quality of Life
Stem cell therapy involves collecting healthy stem cells, preparing them, and injecting them into the body to repair damaged tissues or replace diseased cells. The process includes cell harvesting (bone marrow/blood), laboratory manipulation, and delivery via intravenous infusion or direct injection.
102
Uses of stem cells other than stem cell therapy
Therapeutic Cloning
Induced Pluripotent stem cells
Treatment of Parkinson’s disease + damaged nerves
Treatment of type 1 diabetes
Organs for transplant
103
Uses of embryonic stem cells
Embryonic stem cells
ability to differentiate into almost any cell type
use of embryonic stem cells is banned, even for research or is allowed for research but is very tightly regulated in some countries
embryos used for research are often the waste (fertilised) embryos from IVF
have the potential to develop into human beings => ETHICAL ISSUE
-> Totipotent if taken in the first 3-4 days after fertilisation
-> Pluripotent if taken on day 5
104
Uses of adult stem cells
Adult stem cells
can divide (by mitosis) an unlimited number of times but they are only able to produce a limited range of cell types
small numbers of stem cells remain to produce new cells for the essential processes of growth, cell replacement and tissue repair
donor is able to give permission
need to be a close match in terms of blood type and other body antigens => immune system rejection
Ideally, the patient's own adult stem cells are used to treat them, as there is a much lower chance of rejection
-> Bone marrow - used to produce different types of blood cell
-> Brain - used to produce different types of neural and glial cells
105
Ethics of using embryonic stem cells
viable embryo (an embryo that could become a foetus if implanted in a uterus) being destroyed
disadvantage of only using adult stem cells is that, unlike embryonic stem cells, they are unable to differentiate into all of the specialised cell types (some of which may be required to treat certain diseases)
Embryonic stem cells cannot give consent
Who owns an embryo
106
Cell differentiation
After fertilisation, all cells have the same genetic info => need to express only certain proteins and specialise to form diff tissues
107
Housekeeping genes and differentiation definitions
”Housekeeping genes” - found in all cells, they code for proteins that are essential for the cells (cell membrane proteins, respiratory enzymes)
Differentiation - promotion and suppressing some gene expression
108
Gene Linkage
Each gene is found in its locus -> gene loci are linked if they are on the same chromosome
Linked genes located on human chromosomes 1 to 22 (autosomes) = autosomal linkage
-> 2 or more genes do not assort independently during meiosis (stay together in original parental combination) => passed to offsprings all together
=> During meiosis, closely linked genes will be passed into the gamete as a single unit; loosely linked genes will form some recombinant gametes, with different mixtures of the alleles
109
Dihybrid Cross
Dihybrid Cross - digenic inheritance (inheritance of 2 different characteristics of 2 different genes are inherited completely independently from 2 different chromosomes)
110
Draw a dihybrid cross for 2 heterozygous flies of GgNn genotype
Parent 1 and 2: GgNn (Heterozygous)
4 gametes => GN, Gn, Ng, ng
9:3:3:1
111
Control of gene expression: when?
Can be controlled:
before, during and after transcription and translation
environmental factors
112
How can gene expression be controlled before transcription?
Eukaryotes have transcription factors to control gene expression -> a protein that controls the transcription of genes by binding to a specific region of DNA
Activators - increase the rate at which the gene is expressed
Repressors - decrease the rate gene expression
Some - bind to promoter sequence (found in front of the gene) = stimulates the start of transcription
Some - bind to the enhancer sequences = change the chromatin sequence making it more or less open to RNA polymerase (can be close or far away)
Some control the activity of many or singular gene (can stimulate one and inhibit another at the same time)
-> ensure that the correct gene is expressed in the correct cell at the correct time
-> high control of gene expression against mutations
113
Post-translational gene control
further modification of proteins may occur
protein that is coded may retain intact, shorten or lengthen by enzymes to give a variety of other proteins
114
How can gene expression be controlled before translation?
mRNA contains introns
to produce functional proteins, introns need to be spliced out of the mRNA, leaving only the regions that code for exons
Spliceosome removes the introns from pre-mRNA, producing mature mRNA containing exons only
Can also rearrange the exons
115
E.coli bacteria’s gene expression being influenced by environmental factors
E.coli bacteria can break down lactose (prefers glucose as it requires fewer steps and less energy to break down) ⇒ to use it, it needs to express lac operon genes, which encode key enzymes for lactose uptake and metabolism
-> ONLY expressed when lactose is available and glucose is not
In absence of lactose = RNA polymerase cannot bind to code for beta-galactosidase due to repressor
In presence of lactose = lactose binds to the beta-galactosidase and inactivates it, hence RNA can bind to the DNA sequence and transcribe the code coding for beta-galactosidase
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Epigenetics + epigenome
genetic control by factors other than the best sequences of DNA
-> switching on/off genes, without changing the actual genetic code
=> Epigenome - the modification to DNA molecule that affect its chemical composition of DNA in an entire body
Epigenome is inheritable (when a cell divides for gamete production) or replicates (during mitosis), epigenetic changes affecting the expression of genes in the DNA that a cell may be passed on to daughter cells)
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3 systems that can interact and control genes in response to environ factors:
DNA methylation
Histone modification
Non-coding RNA
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DNA Methylation
addition of methyl group to DNA by DNA methyltransferase enzyme => addition to cytosine base
Methylation of DNA changes the arrangement of the DNA molecule and preventing transcription = silence genes
suppresses the transcription of the affected gene by inhibiting the binding of transcription factors and enzymes needed for transcription (eg RNA polymerase)
DNA methylation can be affected by many environ, lifestyle and age-related factors
Demethylation - removal of the methyl group allows genes to be activated again
Lack of demethylation = associated with cancer
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Histone Modification (methylation and acetylation)
Heterochromatin = chromatin is density supercoiled and condensed (genes are unavailable for transcription as transcription factors cannot access them)
Active chromatin = more loosely packed and less coiled (genes are available for transcription)
Histone acetylation adds an acetyl group (COCH3) to a lysine of the histone structure opening up the chromatin and allowing genes in the area to be transcribed
Deacetylation - removal of the acetyl group allowing DNA to supercoil back
Histone methylation adds an methyl group (CH3) to a lysine of the histone structure => depending on the lysine position, it can either activate or inactivate the region of DNA
Usually, it silences the genes or an entire chromosome
Demethylation - removal of the methyl group allowing DNA to supercoil back/ loosen up
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Non-coding RNA (ncRNA) in gene expression against
non-coding RNA seems to affect the transcription and modify the products of transcription
both genes and chromosomes can be silenced by ncRNAs
ncRNA can coat (wrap around) one of the X-chromosomes in females and deactivate it
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Why does gene expression matters?
Transcription factors and epigenetics affect transcription (allowing genes to be expressed/repressed) at different stages
Only the activated genes are transcribed into the mRNA
mRNA is translated into proteins
Proteins formed are permanently modify the cell and determine its structure and function
The combination of genes that are expressed/ suppressed will determine which cell a stem cell specialises to become
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Monogenic vs Polygenic
-> monogenic (controlled by one gene) = discontinuous variation (present or not)
-> polygenic (controlled by multiple genes) = continuous variation (can be affected by the environment)
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When studying genetic variation in humans:
hard to study variation with humans => need multiple clones that are subjected to very specific and controlled conditions ⇒ UNETHICAL
Improving reliability:
large study sample (avoid to observe a particular trait by chance)
Collect samples from a wide range as possible across organisms habitat
selecting samples from small areas means only getting organisms who are subjected to one environment
data is displayed as graph/ histogram to show frequency distribution clearly
Biology AS
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