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SECTION 3 - CELL STRUCTURE (3.4 EUKARYOTIC CELLS (GOLGI APPARATUS (Golgi…
SECTION 3 - CELL STRUCTURE
3.1 STUDYING CELLS
CELL FRACTIONATION
The process where cells are broken up and organelles are seperated
Tissue placed in a cold, buffered same water potential solution
Reduce enzyme activity
Prevent lysis or crenation
pH does not fluctuate so structure of organelles and enzymes unchanged
Cells broken up by homogenizer to release organelles, making homogenate
Ultracentrifugation is the process of spinning filtered homogenate
A centrifuge spins the tubes so the heaviest organelles fall to the bottom and form a pellet, nuclei first
The supernatant (fluid at top) is removed and spun again, making a mitochondria pellet etc
MAGNIFICATION
Magnification is how many times bigger the image is than the object
Image is appearance when viewed
Object is the material under a microscope
Image height divided by object height equals magnification
Object height times magnification equals image height
RESOLUTION
Minimum distance apart two objects must be in order for them to look separate
Depends on wavelength or radiation used
Increasing magnification increases size of image but not always resolution
3.4 EUKARYOTIC CELLS
Eukaryotic cells have membrane bound organelles and a nucleus
NUCLEUS
Hereditary material, control centre for production of proteins and RNA
Nuclear envelope is a double membrane that controls what goes in and out
Nucleoplasm is granular jelly in the nucleus
The nucleolus is a smal spherical reigon that makes ribosomal RNA
Nuclear pores allow passage of large moelcules
Chromatin are protein pound linear DNA strands
MITOCHONDRION
Sites of aerobic respiration
Responsible for producing ATP
Inner membrane folds to form cristae which increases SA for attachment
The matrix is the middle of the mitochondria, containing proteins, lipids, ribosomes and DNA
CHLOROPLASTS
Organelles that carry out photosynthesis
Chloroplast envelope is a double plasma membrane
Grana are stacks of thylakoids which contain chlorophyll where light absorption takes place
The stroma is the matrix where sugars are synthesised
ENDOPLASMIC RETICULUM
Elaborate 3D system of sheet membranes
Continuous with outer nuclear membrane
RER
Ribosomes on surface
Path for material transport
Large surface area for synthesis
SER
Stores, synthesises and transports lipids/carbs
No ribosomes on surface
Cells that manufacture and store lots of molecules have lots of ER e.g. secretory cells and liver cells
GOLGI APPARATUS
Golgi modifies protein by adding non protein components
Labels them and sends them to the right location
Golgi vesicles are little sacs that transport molecules which may move to the membrane and fuse to release
Golgi apparatus forms glycoproteins
Produces secretory enzymes and carbs
Transports modifies and stores lipids
Forms lysosomes
LYSOSOMES
Vesicles containing enxymes
Also contains lysozymes which hydrolyse cell walls
Hydrolyse materials ingested by phagocytes
Release enzymes out the cell to destroy surrounding material
Autolysis- break down dead cells
In phagocytes
RIBOSOMES
Small cytoplasmic granules
Protein synthesis
80s or 70s
Contain ribosomal RNA and proteins
CELL WALL
Consists of microfibrils of cellulose
Middle lamella is a thin layer which seperates
Mechanical strength to stop bursting form osmosis
VACUOLES
Fluid filled sac bound by a tonoplast
Contains a solution of minerals, sugars, amino acids and wastes
Sometimes contains pigments which make flowers coloured
Turgidity
Maybe temporary food store
3.2-3.3 MICROSCOPES
LIGHT MICROSCOPE
Uses visible light and convex glasses to see
Light passes through the object
Specimens can be live as they don't need staining and don't use a vacuum
Low resolution at 0.2um due to wavelength of light
Image is 2D and coloured
ELECTRON MICROSCOPES
Uses a beam of electrons
Shorter wavelength
High resolving power and solution
A vacuum needs to be used
Object must be dead and stained
SEM
Scanning electron microscope
Beam passed back and forth across a portion which scatters the electrons
Pattern of reflected electrons reflects the surface
Builds up 3D image
Resolving power of 20nm
TEM
May contain artefacts, anomalies form preparation
High resolving power of 0.1nm
Thin parts allow electrons to pass which make them bright, thick parts absorb them so are dark
Electron gun focused with a condensor electromagnet
Transmission electron microscope
2D image
3.7 MITOSIS
Mitosis produces two daughter cells with diploid chromosomes
It's for growth, repair and reproduction of single celled organisms
Mitosis is a divison of the cell that makes individual clones
INTERPHASE- period where cell is not dividing and DNA is replicated
PROPHASE- chromosomes visible, centrioles move to poles and spindle fibres develop from these
METAPHASE- chromosomes visible and arranged at equator
ANAPHASE- sister chromatids pulled apart turning them into chromosomes
TELOPHASE- chromosomes reach poles and spindle fibres disintegrate
CYTOKINESIS- cytoplasm divides
In prokaryotic cells they use binary fission instead
Circular DNA molecule replicates
Plasmids replicate
Cell membrane grows between and pinches
A new cell wall forms to make identical daughter cells
3.8 CELL CYCLE
CELL CYCLE
Regular cycle divided by periods of growth
Interphase, nuclear division, cytokinesis
24 hours with 90% interphase
CANCER
Group of diseases caused by a gorwth disorder in cells that leads to uncontrollable division
A tumor is a group of abnormal cells that develop and expand
These can be malignant or bengign
A mutation in the genes that control rate of mitosis normally dies, but if they survive they can form tumors
CANCER TREATMENT
Cancer is treated by blocking part of the cell cycle
Chemotherapy drugs prevent DNA replication or inhibit metaphase so spindle fibres don't form
Chemo disrupts growth of normal cells, particularly rapidly dividing cells such as hair cells (explains hair loss)
3.5 CELL SPECIALISATION AND ORGANISATION
Cell specialisation is when cells differentiate
Tissues are when a collection of cells that perform a similar function are clumped together
Epithelial tissues that protect and secrete
Xylem in plants
Organs are a combination of tissues that have a major function
Stomach made up of muscles, epithelium, connective tissue
Leaves are an organ made up of palisade mesophyll, spongy mesophyll, epidermis , phloem and xylem
Organ systems are organs that work together as a single unit
Digestive system, respiratory system, circulatory system
3.6 PROKARYOTIC CELLS AND VIRUSES
The secreted capsules protects from other cells and allows groupings for extra security
Plasmids are individual rings of DNA that can reproduce for immunity
In prokaryotes there are plasmids, no membrane bound organelles, no chloroplasts, 70s ribosomes, a murein cell wall and maybe a capsule
Prokaryotic cells are smaller with no nucleus or nuclear envelope
The cell wall acts as a physical barrier from lysis, substances, mechanical damage
VIRUSES
Acellular non living particles that only multiply inside host cells
Contain nucleic acids contained by the capsid which had attachment proteins on the surface