Cells Flashcards
Describe the process of cell fractionation to separate organelles of a cell
- Tissue homogenization to break open cells and release organelles
- Filter homogenate to remove debris or whole cells
- Use isotonic solution which has same water potential organelles to prevent them from bursting to shrinking from osmosis
- Keep cold to slow down enzyme activity
- Centrifuge at low speed to separate heavy organelles, eg nuclei
- Re-spin supernatant at progressively higher speeds / for mention which pellet contains desired organelles
Describe how TEM works
- beams of electrons penetrate specimen and focused using electromagnets
- denser parts absorb more elections
- so they appear darker in the electron micrograph
Role of Golgi Apparatus
- involved in secretion
- modifies polypeptide to form protein
- adds lipid/ carbohydrate groups
- packages into Golgi vesicle
- transports to cell surface
Role of Mitochondria
- Aerobic respiration
- RELEASES energy
(produces=no mark) - Produces ATP
Organelles in Eukaryotic cells only
- Nucleus
- Mitochondria
- Endoplasmic Reticulum
- Lysosome
Test for starch
- add iodine
- turns blue-black from orange
Mitochondria
- sites of aerobic respiration
- produce ATP or release energy
no mark for PRODUCE energy
Cell fractionation - why is solution cold
- slow down enzyme activity
- to prevent DIGESTION (not damage) of organelles
Cell fractionation - why is solution isotonic
- same water potential as organelles
- to prevent lysis (bursting) from osmosis
Magnification
How many times larger the object appears compared to its actual size
Resolution
The minimum distance apart two objects can be for them to appear as two distinct objects
Cell fractionation - buffered
- pH does not change
- structure of organelles is not altered
- enzyme function is unaffected
Differences between eukaryotic and prokaryotic cells
- no nucleus vs membrane bound nucleus
- no membrane bound organelles vs several, eg mitochondria and ER
- DNA not associated with proteins vs histones
- 70s vs 80s ribosomes
- capsule vs none
- cell made from murein vs cellulose (if present)
Nucleolus function
- synthesises ribosomal RNA
- manufactures ribosomes
Nucleus function
- contains all genetic material
- manufactures rRNA and ribosomes in nucleolus
- controls DNA replication during cell division
- controls gene expression > site of transcription
Cristae
- inner membrane of mitochondrion
- provides a large surface area for attachment of enzymes for respiration
Adaptations of chloroplast
- granal membrane has large surface area for attachment of chlorophyll and enzymes
- stroma fluid posses all enzymes to synthesis sugars
- chloroplasts contain DNA and ribosomes to quickly manufacture proteins for photosynthesis
Difference between RER and SER
- RER has ribosomes but SER does not
- RER synthesises proteins
- SER store proteins and synthesises lipids and steroid hormones
- RER is attached to nuclear envelope but SER is not
Lysosome function
- hydrolyse material ingested by phagocytes
- digest worn out organelles
- autolysis (break down dead cells) and exocytosis (destroy material around cell)
Centrioles
Hollow, cylindrical tubes used in the production of spindle fibers
Vacuole function
- makes cell turgid
- mineral salts and sugars are food store
- pigments attract pollinating insects
Capsule function
- mucilaginous layer of slime
- protects from other cells
- or helps groups stick together for further protection
Plasmid function
- small circular pieces of DNA
- replicate independently of nucleoid
- possess genes to aid survival (e.g. antibiotic resistance)
- transferred between bacteria
Describe how bacteria divide
- binary fission
- circular DNA replicates and copies attach to cell membrane on opposite poles of cell
- plasmids replicate
- cell membrane forms in between and cytoplasm divides forming two daughter cells
- each with a single copy of circular DNA
Virus - accellular
- no cell-surface membrane
- very few organelles
- lack ability to reproduce alone
Virus - non living
- cannot reproduce alone
- no metabolism
Describe viral replication
- viruses attach to host cell + inject viral genetic material
- viral genome replicated (host cell DNA broken down)
- transcription and translation of viral genome using components of host cell to assemble more viruses
- cell lysis to release viruses
Artefacts
Features not part of the specimens that results form the preparation process, eg scratches, bubbles
Calibrating graticule
Align with microscope slide called stage micrometer
Mitosis
Cell division to make two GENETICALLY identical daughter cells
Explain all stages of interphase
G1 - cell grows and continues with normal cell function
S - DNA replication (form identical sister chromatids)
G2 - cell grows and replicates organelles
Centromere
Part of chromosomes where sister chromatids are held together
Mitosis Process
Interphase - DNA replication creates identical sister chromatids Prophase -chromosomes coil and because fatter/shorter (visible) - spindle fibers form - nuclear envelope breaks down Metaphase - spindle fibers attach to centromere - chromosomes line up in middle Anaphase - centromere divides - spindle fibers contract + pull identical sister chromatids to opposite poles Telophase - two sets of chromosomes on opposite poles - new nuclear envelope - chromosome becomes long/thin Cytokinesis - cytoplasm divides
Evaluate asexual reproduction
- fewer stages so faster
- produces clones
- entire population susceptible to disease
Evaluate sexual reproduction
- creates genetic variation which aids survival of species
- natural selection removes disadvantageous alleles
- requires two parents
- requires time and energy
- not all favourable genes passed to offspring
Compare TEM/SEM and OM
- OM uses light and TEM uses electron beam
- TEM has no colour but OM shows specimen in colour
- TEM / SEM has higher resolution and magnification than OM
- TEM allows internal structures of organelles to be observed compared to OM
- OM allows for living specimen where TEM/SEM is dead only (require vacuum in tube)
- TEM requires thinner specimens compared to OM
- OM is simple specimen preparation where TEM/SEM is complex (requiring specialist equipment / training)
- OM has fewer artefacts where TEM/ SEM has many due to preparation process
- TEM is higher resolution / magnification than SEM
- SEM produces 3D images
- SEM allows surface of specimen to be viewed
Difference between DNA found in prokaryotic compared to eukaryotic cells
- not associated with histones / no chromosomes
- non linear
- no introns
Suggest how to distinguish between smooth endoplasmic reticulum and Golgi body diagrammatically
- smooth endoplasmic reticulum surround nucleus and extends from rough endoplasmic reticulum
- Golgi body is found in the cytoplasm
Describe how a polypeptide exits the cell as a functional protein
- polypeptide synthesised by ribosomes on RER
- travels in vesicle of RER to Golgi body
- modified at Golgi body to form protein
- carried by Golgi vesicle to cell surface for secretion
Compare structure of chloroplast and mitochondria
similarities
- double membrane
- large surface area
- contain DNA and RNA
- contain similar coenzymes
- contain membranes embedded with electron transport proteins and enzymes
differences
- C contains photosynthetic pigments but M does not
- C has smooth inner and outer membrane but M has highly folded inner membrane
- C has membrane bound thylakoids (grana) but M folded into cristae
Describe how lysosomes are formed
Golgi vesicle containing lysozymes (enzymes) fuses with endosomes (vesicles containing material taken up by cell)
Retrovirus
- RNA genetic material / contain reverse transcriptase
- replicate in host cells by reverse transcription
Cell fractionation - buffered
enzymes/proteins do not DENATURE
