2.1 and 2.2 Flashcards
What are the distinguishing features of eukaryotic cells?
Cytoplasm containing membrane-bound organelles, so DNA enclosed in a nucleus
Describe the structure of the cell-surface membrane:
Phospholipid bilayer. Hydrophilic phosphate heads point to/attracted to water and hydrophobic fatty acid tails point away/repelled from water
Describe the function of the cell-surface membrane:
Nuclear envelope- double membrane, has nuclear pores
Nucleoplasm
Nucleolus
Protein/histone-bound, linear DNA- chromatin=condensed, chromosome=highly condensed
Describe the function of the nucleus:
Holds/stores genetic info which codes for polypeptides (proteins)
Site of DNA replication
Site of transcription, producing mRNA
Nucleolus makes ribosomes/rRNA
Describe the structure of a ribosome:
Made of ribosomal RNA and protein
Not a membrane-bound organelle
Describe the function of a ribosome:
Site of protein synthesis (translation)
Describe the function of rough (rER) and a smooth endoplasmic reticulum:
rER: ribosomes on surface synthesis proteins
proteins processed/folded/transported inside rER
proteins packaged into vesicles for transport
sER: synthesises and processes lipids e.g. cholesterol and steroid hormones
Describe the structure of the golgi apparatus and vesicles:
Flattened membrane sac. Vesicle is small membrane sac
Describe the function of the golgi apparatus and golgi vesicles:
Modifies proteins
modifies lipids
packages proteins/lipids into vesicles
produces lysosomes
vesicles transport proteins/lipids to their required destination, moves and fuses with cell membrane
Describe the structure and function of lysosomes:
Type of vesicle with hydrolytic enzymes
Release hydrolytic enzymes (lysozymes) to break down/hydrolyse pathogens or worn-out cell components
Describe the structure of mitochondria:
Outer membrane, inner folded membrane (cristae), matrix containing 70s ribosomes and circular DNA
Describe the function of mitochondria:
SIte of aerobic respiration
To produce ATP for energy release
Describe the structure of chloroplasts in plants/algae:
Double membrane
Stroma containing thylakoid membrane, 70s ribosomes, circular DNA, starch granules
Lamella- thylakoid linking grana
Grana- stacks of thylakoid
Describe the function of chloroplasts in plants/algae
Absorbs light energy for photosynthesis
To produce organic substances
Describe the structure and function of the cell wall in plants, algae and fungi
In plants/algae composed mainly of cellulose
In fungi composed of chitin
provides mechanical strength to cell, so prevents cell changing shape or bursting under pressure
Describe the structure and function of cell vacuole:
Tonoplast membrane, contains cell sap
Maintains turgor pressure in cell
Contains cell sap- stores sugars, amino acids, pigments and any waste chemicals
Describe how eukaryotic cells are organised in complex multicellular organisms:
Tissue- group of specialised cells with a similar structure, working together to perform a specific function, often with same origin
Organ- aggregations of tissues, performing specific functions
Organ system- group of organs working together to perform specific functions
What are the distinguishing features of prokaryotic cells?
Cytoplasm lacking membrane bound organelles so genetic material not enclosed in a nucleus
Describe the structure of prokaryotic cells:
ALWAYS: cell surface membrane, murein cell wall, 70s ribosomes, circular DNA
SOMETIMES: Capsule, plasmids and flagella
Why are viruses described as acellular and non-living?
Acellular- not made of cells, no cell membrane/cytoplasm/organelles
Non-living - no metabolisms, cannot independently respire/move/replicate/excrete
Describe the general structure of a virus particle:
Nucleic acids surrounded by a capsid
Attachment proteins allow attachment to specific host cells
No cytoplasm, ribosome, cell wall, cell membrane etc
Some also surrounded by a lipid envelope
Define magnification and resolution:
Magnification= number of times greater image is than size of real object
Magnification=image/actual
Resolution= minimum distance apart 2 objects can be to be distinguished as separate objects
How does an optical microscope work?
Light focused using glass lenses, passes through specimen and different structures absorb different amounts and wavelengths
Generates a 2d image of a cross section
Low resolution due to long wavelengths
Can’t see internal structures of organelles or ribosomes
Specimen=thin
Low magnification x1500
Can view living organisms
simple prep
colour
How do TEM work?
Electrons focused using electromagnets
Pass through specimen, darker parts absorb more and appear darker
Generates a 2D image of a cross sections
Very high resolution due to short wavelength
Can see internal structures of organelles and ribosomes
Specimen=very thin
High magnification x1000000
Dead/dehydrate specimens as uses a vacuum
Complex prep so artefacts often present
No colour
How does an SEM work?
electrons focused using electromagnets
Deflected/bounce off specimen
3D image of surface
High resolution due to short wavelength
Can’t see internal structures
No need to be thin
High magnification x1000000
Dead/dehydrate specimens as vacuum
Complex prep so artefacts
No colour
Describe how the size of an object viewed with an optical microscope can be meausred:
Line up eyepiece graticule with stage micrometre
Calibrate eyepiece graticule- use stage micrometer to calculate size of divisions on eyepiece graticule
Take micrometre away and use graticule to measure how many divisions make up object
Calculate size of object by multiplying no. divisions by size of division
Recalibrate eyepiece graticule at different magnifications
Describe and explain the principles of cell fractionation and ultracentrifugation :
- Homogenise tissue/use blender
- disrupts cell membrane, breaking open cells and releasing contents/organelles - Place in a cold, isotonic, buffered solution
- cold to reduce enzyme activity
- isotonic so water doesnt move in/out organelles by osmosis (don’t burst)
- buffered to keep pH constant so enzymes don’t denature - Filter homogenate
- remove large, unwanted debris - Ultracentrifugation separates organelles in order of density/mass
- centrifuge at high speed
- remove pellet of heaviest and respin supernatant at a higher speed
- repeat and increasing speed
nuclei, chloroplasts, mitochondria, lysosomes, endoplasmic reticulum, ribosomes
Describe the stages of the cell cylce in eukaryotic cells:
- Interphase
- DNA replicates semiconservatively leading to two chromatids joined at a centromere
- number of organelles and volume of cytoplasm increases, protein synthesis - Mitosis
- nucleus divides
- to produce 2 identical nuclei - Cytokinesis
- cytoplasm and cell membrane divide
- forms 2 new genetically identical daughter cells
Describe the behaviour of chromosomes and the role of spindle fibres in mitosis:
- Prophase
- chromosomes condense, becoming shorter/thicker so appear as 2 sister chromatids joined by a centromere
- nuclear envelope breaks down
- centrioles move to opposite poles forming spindle network - Metaphase
- spindle fibres attach to chromosomes by their centromeres
- chromosomes align along equator - Anaphase
- spindle fibres shorten/contract
- centromere divides
- pulling chromatids to opposite poles of cell - Telephase
- chromosomes uncoil becoming longer/thinner
- nuclear envelopes reform = 2 nuclei
- spindle fibres/centrioles break down
Why do some eukaryotic cells not undergo the cell cycle?
Within multicellular organisms, some cells lose the ability to divide (e.g neurons)
Only cells that do retain this ability go through a cell cycle
Explain the importance of mitosis in the life of an organism:
Growth of multicellular organisms
Replacing cells to repair damaged tissues
Asexual reproduction
Describe how tumours and cancers form:
Mutations in DNA/genes controlling mitosis can lead to uncontrolled cell division
Tumour formed if this results in mass of abnormal cells
- malignant=cancerous, can spread
- benign= non-cancerous
Suggest how cancer treatments control rate of cell division:
Some disrupt spindle fibre activity/formation
- so chromosomes can’t attach to spindle by their centromere
- so chromatids can’t be separated to opposite poles
- so prevents/slows mitosis
Some prevent DNA replication during interphase
- so can’t make 2 copies of each chromosme
- so prevents/slows mitosis
Describe how prokaryotic cells replicate:
Binary fission:
Replication of circular DNA
Replication of plasmids
Division of cytoplasm to produce 2 daughter cells
- single copy of circular DNA but variable number of copies of plasmids
Describe how viruses replicate:
- Attachment proteins attach to complementary receptors on host cell
- Inject viral nucleic acid into host cell
- Infected cell replicates virus particles
- nucleic acid replicated
- cell produces viral protein/capsid/enzymes
- virus assembled then released
