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TOPIC 1
Cell theory:
- All living things are composed of cells
- Cells are the Smallest unit of life, and can function on its own
- Cells come from preexisting cells - by multiplying
Exceptions
- Giant algae: shows that cell not smallest unit of life as it can grow to about 100nm but
only has one nuclei instead of being composed of many cells.
- Aseptate fungi hyphae: hyphae (thread like structure on fungi) has one continuous
cytoplasm no septa (walls separating into discrete cells) so multinucleated. Living
structure not composed of discrete cells
- Striated muscle fibre. Fibres enclosed in membrane but 300nm and multinucleated.
Not smallest unit of life
Functions of life: metabolism, response, Homeostasis, growth, reproduction, excretion,
nutrition
Paramecium
M: secretes enzyme in cytoplasm to break down food
R: uses cilia to move away when it touches solid object
H: homeostasis: vacuoles to release water to maintain internal conditions
G: feeding to increase in size and dry mass
R: reproduces aexually via mitosis (nucleus divides to facilitate)
E: diffusion of waste products through plasma membrane
N: obtains nutrients by digesting in vesicles via endocytosis
Chlorella (photosynthetic unicellular organism)
M: secretes enzyme to catalyse chemical reactions in cytoplasm
R: cilia to move towards light
H: vacuoles expel water
G: absorption of minerals and photosynthesis causes cell to increase
E: expel waste product like oxygen through plasma membrane stroma
N: produces own nutrients by photosynthesis in chloroplast
Multicellular organisms - advantage
- Increased SA:V ratio so more efficient diffusion, faster bc less distance.
- Concentration gradient is easier to generate
- If big cell: low SA:V ratio, cannot obtain or excrete products quick enough
Emergent properties
- Whole is greater than the sum of its parts
- Cells function on its own but combined functioning of cell makes it better
Differentiation to specialised tissue
- All cells have same genome so has potential to become any specialised tissue
- Some genes are turned off and some specific genes are expressed
, - Causing specialisation into specific cell (eg neuron or epithelial cell) that can't be
reversed.
Stem cells +ethics
- Cells w capacity to divide and differentiate into any pathway
- Totipotent: extremely rare, only in early stage of zygote development, can
differentiate into any cell
- Multipotent: differentiate into almost any cell. Found in blastocyst/early embryo
- Pluripotent: can differentiate into some specialised cells (the closely related family of
cells)
- Found in bone marrow, skin and liver, baby umbilical cord/placenta.
- Using stem cells can improve quality of life of those suffering
- Can only obtain embryonic stem cells by destruction of embryo which may be seen
as immoral
- Early stage embryo dont have nervous system so won’t feel it
- Large numbers of embryo produced for IVF and never implanted so better to use it
than discard it
Therapeutic uses
Stargardts
- Due to recessive mutation in gene causing malfunction of retinal cells in
photoreceptor to the point where classified as blind
- Embryonic stem cells taken and injected into eye while under anesthesia
- Embryonic stem cell attaches to retina and begin to replicate into functioning
cell
Leukaemia
- Abnormally high number of white blood cells produced in the bone marrow
- Adult donor stem cells stored in fridge until injection
- Large needle inserted into the pelvis to extract the cells
- Drugs given for chemotherapy to patient to kill all cancer cells and prevent
further production of blood cells
- Donor cells injected and reestablished in bone marrow. Will multiply and
produce red and white blood cells normally
- Completely cured of leukemia.
Electron microscopes higher resolution than light microscope. But e microscope can’t be
viewed in colour
Magnification = scalebar length (micrometres)/actual length of specimen
1000 micrometers= 1 millimetre
Prokaryotes
- Not compartmentalised unlike eukaryotes
- No nucleus or mitochondria or chloroplast (double membrane) or any single
membrane bound organelles
Divide by binary fission
- Replicate chromosomes (semi conservative). Cell elongates. Chromosome moves to
opposite ends. Plasma membrane pinches in. furrow forms. Two separate identical
daughter cells
,Drawing: cell wall, pilli, flagella, plasma membrane, cytoplasm, 70s ribosomes, nucleiod w
naked DNA
Eukaryotes: plasma membrane, cytoplasm, 80s ribosomes, nucleus, mitochondria
Advantage of compartmentalisation:
- Enzymes and substrates needed in process can be concentrated in a small area w
specific pH and other optimum lvls, won’t be disrupted by other enzymes.
Function of organelles:
- Ribosome: location of protein synthesis
- Cytoplasm: fluid where metabolic process take place and fills the cell
- Plasma membrane: semi permeable barrier that controls what enters and exits
Prokaryote only:
- Plasmid: small circles of DNA can be used in gene transfer and provides antibiotic
resistance
- Pilli: cell adhesion/attachment to surface
- Flagellum: movement of cell -locomotion
- Nucleoid region: where reproduction occurs and controls cell’s activities
- Cell wall: protects the cell and prevents bursting
Eukaryote only:
- Nucleus: controls cell activities and reproduction
- Mitochondria: where ATP is generated by cellular respiration
- Endoplasmic reticulum: smooth ER produces lipids and rough ER produces protein
(eg enzyme) for transport outside of cell
- Golgi apparatus: near cell membrane. process and packages protein to be released
out of the cell through golgi vesicles
- Centrosome: radiate microtubules from spindle fibres (pair of centrioles in a cell not p
cell)
Plant only:
- Cell wall: protecting cell and prevent bursting
- Chloroplast: where photosynthesis occurs
Animal only:
- Lysosome: hydrolytic enzymes for breakdown of macromolecules.digests old
organelles
Phospholipids: amphipathic. Hydrophobic tail, hydrophilic head
- Bilayer: hydrophobic fatty acid tails sandwiched in middle w hydrophobic head facing
outside. orientates naturally when touches water
- Davson danielli model (wrong):
Phospholipid bilayer with a layer of protein on either side
Electron micrographs used to confirm theory. Saw two dark lines which they thought
was protein membrane as it usually appeared darker than the phospholipids
- Singer-nicolson theory- fluid mosaic model: phospholipid bilayer had membrane
proteins embedded in it
Freeze fracture electron micrographs showed globular proteins were present in
centre of bilayer
Some proteins would be hydrophobic in parts so would be positioned in the bilayer
, Fluorescent markers tagged two different membrane proteins red and green. Cell
fused and red and green mixed showing protein could move in bilayer.
The layer was rough and varied in size so could not form one smooth layer around
the membrane surface. Thus falsifying davson danielli model.
- Membrane proteins
Integral protein: embedded in bilayer, permanently attached
- Hormone receptors (eg insulin, glucagon other peptide based)
- Calcium pumps for active transport
- Channels for passive transport / facilitated diffusion
- Proton pumps
- Electron carrier
- Cell adhesion
- Neurotransmitter receptor.
Glycoprotein: have sugar unit attached on outer surface of membrane
peripheral protein: attached to outer surface of membrane. Temporarily attached
- Enzymatic activity: for electron transport chain
- Cholesterol: only in animal cells, adds stability (plant cells have cellulose for this) fits
btw phospholipid as there is also a hydrophobic (steroid ring and hydrocarbon tail)
and hydrophilic end (-OH group)
cholesterol prevents crystalisation of membrane by separating the phospholipd tails
Immobilises outer surface of membrane - Decreases membrane fluidity
Reduces permeability to small water-soluble molecules that could otherwise cross.
Necessary to maintain conc gradient.
Simple diffusion: passive process moving particles from a region of high conc to low conc
across a partially permeable membrane
Facilitated diffusion: still passive process as no energy is required but specific channel
proteins in the membrane can allow one specific substance to pass through.
Osmosis: passive movement of water from region of low solute conc to high solute conc
across a partially permeable membrane down conc. Gradient. Passive bc water molecules
are small enough to pass through the membrane
Active transport: movement of particles from an area of low to high conc against conc
gradient. Not passive process, requires ATP
- Pump proteins are very specific. Activated by ATP binding which causes change of
shape of protein to transport the substance across. Then ADP and phosphate
released and pump returns to original shape.
- Sodium-potassium pump; antiporter as ions pumped ot opposite directions
Vesicle transport (endo and exocytosis)
- Endo: membrane pulled in/ pinches in and a drop of fluid becomes enclosed in a
vesicle when the membrane pinches off. Vesicle then travels in cytoplasm
- Transporting protein: protein synthesised on ribosomes and pass through the rER.
Vesicles bud off from the rER and transport the protein to golgi apparatus. Vesicle
fuse w the membrane of golgi apparatus. Golgi packages the protein and vesicles
transport the modified protein through cytoplasm to the cell membrane.
- Exo: vesicles fuse w membrane. Vesicle content is expelled. Membrane becomes flat
again
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