cells Flashcards
What are the distinguishing features of eukaryotic cells?
● Cytoplasm containing membrane-bound organelles
● So DNA enclosed in a nucleus
General structure of eukaryotic cells
Cell surface mem
Mitochondria
Nucleus
Ribosomes
Rer
Ser
Golgi app
Lysosome
Plant only : chloroplast
Cell wall (plants algae fungi
Cell a couple in plants
Describe the structure of the cell-surface membrane
Phospholipid bilayer
- hydrophilic phosphate heads are attracted to water pointing towards
- hydrophobic fatty acid tails point away/repelled by water
Describe the function of the cell-surface membrane
● Selectively permeable → enables control of passage of substances in / out of cell
● Molecules / receptors / antigens on surface → allow cell recognition / signalling
Struc of nucleus
Nuclear envelope
- double mem
- nuclear pores
Nucleoplasm
Nucleolus
- dense region
Protein/histone bound, linear DNA
- chromatin = condensed
- chromosome + highly condensed
Describe the function of the nucleus
● Holds / stores genetic information which codes for polypeptides (proteins)
● Site of DNA replication
● Site of transcription (part of protein synthesis), producing mRNA
● Nucleolus makes ribosomes / rRNA
Describe the structure of a ribosome
● Made of ribosomal RNA and protein (two subunits)
● Not a membrane-bound organelle
Describe the function of a ribosome
Site of protein synthesis (translation)
Struc of ser vs rer
Both are stem of membranes , rough er has ribosomes studded in mem/cisternae
Function of rer
● Ribosomes on surface synthesise proteins
● Proteins processed / folded / transported inside rER
● Proteins packaged into vesicles for transport eg. to Golgi apparatus
Function of ser
● Synthesises and processes lipids
● Eg. cholesterol and steroid hormones
Structure of Golgi app and vesicles
Golgi app - flattened membrane sacs
Golgi vesicle - small mem sacs
Function of Golgi app
● Modifies protein, eg. adds carbohydrates to produce glycoproteins
● Modifies lipids, eg. adds carbohydrates to make glycolipids
● Packages proteins / lipids into Golgi vesicles
● Produces lysosomes (a type of Golgi vesicle)
Golgi
vesicles function
● Transports proteins / lipids to their required destination
● Eg. moves to and fuses with cell-surface membrane
Structure of lysosomes
Circular organelle
Hydrolyic enzymes (lysozymes) surrounded by mem
Describe the function of lysosomes
● Release hydrolytic enzymes (lysozymes)
● To break down / hydrolyse pathogens or worn-out cell components
Describe the structure of mitochondria
Outer mem
Cristae (inner mem fold)
Matrix
- small 70s ribosomes
- circ dna
Describe the function of mitochondria
● Site of aerobic respiration
● To produce ATP for energy release
● Eg. for protein synthesis / vesicle movement / active transport
Describe the structure of chloroplasts in plants and algae
Double mem
Stroma
- thylakoid mem
- small 70s ribosomes
- circ dna
- starch granules/lipid droplets
Lamella (thylakoid linking grana)
Grana (stacks of thylakoid)
Describe the function of chloroplasts in plants and algae
● Absorbs light energy for photosynthesis
● To produce organic substances eg. carbohydrates / lipids
Describe the structure of the cell wall in plants, algae and fungi
● Composed mainly of cellulose (a polysaccharide) in plants / algae
● Composed of chitin (a nitrogen-containing polysaccharide) in fungi
Describe the function of the cell wall in plants, algae and fungi
● Provides mechanical strength to cell
● So prevents cell changing shape or bursting under pressure due to osmosis
Describe the structure of the cell vacuole in plants
Cell sap surrounded by Tonoplast mem
Describe the function of the cell vacuole in plants
● Maintains turgor pressure in cell (stopping plant wilting)
● Contains cell sap → stores sugars, amino acids, pigments and any waste chemicals
What is a tissue
Group of specialised cells with a similar structure working together
to perform a specific function, often with the same origin
Organ
Aggregations of tissues performing specific functions
What is an 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 general structure of prokaryotic cells
Always present
- cell surface mem
- cell wall (Murein glycoprotein)
- cytoplasm
- small 70s ribosomes
- circ dna (free in cytoplasm - not associated with proteins)
Compare and contrast the structure of eukaryotic and prokaryotic cells
Has membrane-bound organelles
eg. mitochondria, endoplasmic reticulum
Vs No membrane-bound organelles
eg. no mitochondria, endoplasmic reticulum
Has a nucleus Containing DNa Vs No nucleus
DNA is is free in cytoplasm v2 DNA is long & linear
& associated with histone proteins
DNA is short & circular
& not associated with proteins
Larger (80S) ribosomes (in cytoplasm) vs Smaller (70S) ribosomes
Cell wall only in plants, algae and fungi
Containing cellulose or chitin
Vs Cell wall in all prokaryotic cells
Containing murein, a glycoprotein
Plasmids / capsule never present
(sometimes flagella)
Vs Plasmids, flagella and a capsule
sometimes present
Larger overall size vs Much smaller overall size
Explain why viruses are described as acellular and non-living
● Acellular- not made of cells, no cell membrane / cytoplasm / organelles
● Non-living- have no metabolism, cannot independently move / respire / replicate / excrete
Describe the general structure of a virus particle
- Nucleic acids surrounded by a capsid
(protein coat) - Attachment proteins allow attachment
to specific host cells - No cytoplasm, ribosomes, cell wall,
cell-surface membrane etc. - Some also surrounded by a lipid
envelope eg. HIV
Describe the difference between magnification and resolution
● Magnification = number of times greater image is than size of the real (actual) object
○ Magnification = size of image / size of real object
● Resolution = minimum distance apart 2 objects can be to be distinguished as separate objects
How is light/electrons focused in optical vs tem vs sem
Light focused through glass lenses vs electrons focused through electromagnets in tem and sem
How is light/electrons passed through specimen in diff types of microscopes
Light passes through specimen diff struc absorb diff amounts and wavelengths
In tem electrons pass through specimen and denser parts absorb more so appear darker
In sem electrons are deflected/bounce off of specimens surface
2d/3d image in all 3 microscopes
Sem - 3D image of a surface
Optical and tem - 2d image of a cross section
Resolution in different types of microscopes and why
Low resolution in optical mic due to long wavelength of light
Very high resolution in tem - short wavelength of e-
High res in sem - short wavelength of e-
Can or can’t see internal struc in 3 types of mic
Can’t see internal struc in optical or sem, can see in tem
Thin specimen in 3 types
Very thin specimens in tem
Doesn’t matter in sem
Thin in optical
Magnification in 3 types of mic
Low mag x1500 in light
High mag x1000000 in tem and sem
Living or dead organisms in 3 types of microscope
Optical - can view living
Tem/sem - has to be dead/dehydrated specimens in vacuum
Prep in 3 types of microscopes
Simple prep in light mic
Complex preparation so
artefacts often present in tem and sem
Colour in 3 different microscopes
Colour in optical no colour in sem or tem
Suggest how the scientific community distinguished between artefacts (eg.
dust, air bubbles occurring during preparation) and cell organelle
● Scientists prepared specimens in different ways
● If an object was seen with one technique but not another, it was more likely to be an artefact than an
organelle
Convert between units
Metre
Milimetre
Micrometer
Nanometre
Going down x1000
Going up divide by 1000
Describe how the size of an object viewed with an optical microscope can be
measured
- Line up (scale of) eyepiece graticule with (scale of) stage micrometre
- Calibrate eyepiece graticule - use stage micrometre to calculate size of divisions on eyepiece graticule
- Take micrometre away and use graticule to measure how many divisions make up the object
- Calculate size of object by multiplying number of divisions by size of division
- Recalibrate eyepiece graticule at different magnifications
Describe and explain the principles of cell fractionation and
ultracentrifugation as used to separate cell components
- Homogenise tissue /
use a blender
● Disrupts the cell membrane, breaking open cells to release
contents / organelles - Place in a cold,
isotonic, buffered
solution
● Cold to reduce enzyme activity
○ So organelles not broken down / damaged
● Isotonic so water doesn’t move in or out of organelles by osmosis
○ So they don’t burst
● Buffered to keep pH constant
○ So enzymes don’t denature - Filter homogenate ● Remove large, unwanted debris eg. whole cells, connective tissue
- Ultracentrifugation-
separates organelles
in order of density /
mass
● Centrifuge homogenate in a tube at a low speed
● Remove pellet of heaviest organelle and respin supernatant
at a higher speed
● Repeat at increasing speeds until separated out, each time the
pellet is made of lighter organelles (nuclei → chloroplasts /
mitochondria → lysosomes → ER → ribosomes)
Summarise the stages of the cell cycle in eukaryotic cells
Interphase - dna replicates semi conservatively (s phase)
- 2 chromatids (identical copies) joined at centromere
- number of organelles and volume of cytoplasm increases, protein synthesis (g1/g2)
Mitosis - nucleus divides
- 2 nuclei produced with identical copies of DNA produced by parent cell
Cytokinesis - cytoplasm and cell mem divide to form 2 genetically identical daughter cells
Describe the behaviour of chromosomes & role of spindle fibres in mitosis
Stage 1
Prophase
• Chromosomes condense, becoming shorter / thicker so visible
Appear as 2 sister chromatids joined by a centromere
• Nuclear envelope breaks down
• Centrioles move to opposite poles forming spindle network
• Spindle fibres start to attach to chromosomes by their centromeres
Stage 2
Metaphase
• Spindle fibres attach to chromosomes by their centromeres
• Chromosomes align along equator
Stage 3
Anaphase
• Spindle fibres shorten / contract
• Centromere divides
Pulling chromatids (from each pair) to opposite poles of cell
Stage 4
Telophase
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, not all cells retain the ability to divide (eg. neurons)
● Only cells that do retain this ability go through a cell cycle
Explain the importance of mitosis in the life of an organism
Parent cell divides to produce 2 genetically identical daughter cells for:
● Growth of multicellular organisms by increasing cell number
● Replacing cells to repair damaged tissues
● Asexual reproduction
Describe how tumours and cancers form
Mitosis is a controlled process so:
● Mutations in DNA / genes controlling mitosis can lead to uncontrolled cell division
● Tumour formed if this results in mass of abnormal cells
○ Malignant tumour = cancerous, can spread (metastasis)
○ Benign tumour = 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 (no anaphase)
○ So prevents / slows mitosis
● Some prevent DNA replication during interphase
○ So can’t make 2 copies of each chromosome (chromatids)
○ So prevents / slows mitosis
Describe how prokaryotic cells replicate
Binary fission:
1. Replication of circular DNA
2. Replication of plasmids
3. Division of cytoplasm to produce 2 daughter cells
○ Single copy of circular DNA
○ Variable number of copies of plasmids
Describe how viruses replicate
Being non-living, viruses do not undergo cell division
1. 2. 3. Attachment proteins attach to complementary receptors on host cell
Inject viral nucleic acid (DNA/RNA) into host cell
Infected host cell replicates virus particles:
a. Nucleic acid replicated
b. Cell produces viral protein / capsid / enzymes
c. Virus assembled then released
Describe the fluid-mosaic model of membrane structure
● Molecules free to move laterally in phospholipid bilayer
● Many components - phospholipids, proteins,
glycoproteins and glycolipids
Describe the arrangement of the components of a cell membrane
● Phospholipids form a bilayer- fatty acid tails face inwards, phosphate heads face outwards
● Proteins
○ Intrinsic / integral proteins span bilayer eg. channel and carrier proteins
○ Extrinsic / peripheral proteins on surface of membrane
● Glycolipids (lipids with polysaccharide chains attached) found on exterior surface
● Glycoproteins (proteins with polysaccharide chains attached) found on exterior surface
● Cholesterol (sometimes present) bonds to phospholipid hydrophobic fatty acid tails
Explain the arrangement of phospholipids in a cell membrane
● Bilayer, with water present on either side
● Hydrophobic fatty acid tails repelled from water so point away from water / to interior
● Hydrophilic phosphate heads attracted to water so point to water
Explain the role of cholesterol (sometimes present) in cell membranes
● Restricts movement of other molecules making up membrane
● So decreases fluidity (and permeability) / increases rigidity
Suggest how cell membranes are adapted for other functions
● Phospholipid bilayer is fluid → membrane can bend for vesicle formation / phagocytosis
● Glycoproteins / glycolipids act as receptors / antigens → involved in cell signalling / recognition
Describe how movement across membranes occurs by simple diffusion
● Lipid-soluble (non-polar) or very small substances eg. O2, steroid hormones
● Move from an area of higher concentration to an area of lower conc., down a conc. gradient
● Across phospholipid bilayer
● Passive - doesn’t require energy from ATP / respiration (only kinetic energy of substances)
Explain the limitations imposed by the nature of the phospholipid bilayer
● Restricts movement of water soluble (polar) & larger substances eg. Na
+ / glucose
● Due to hydrophobic fatty acid tails in interior of bilayer
Describe how movement across membranes occurs by facilitated diffusion
● Water-soluble / polar / charged (or slightly larger) substances eg. glucose, amino acids
● Move down a concentration gradient
● Through specific channel / carrier proteins
● Passive - doesn’t require energy from ATP / respiration (only kinetic energy of substances
Explain the role of carrier and channel proteins in facilitated diffusion
● Shape / charge of protein determines which substances move
● Channel proteins facilitate diffusion of water-soluble substances
○ Hydrophilic pore filled with water
○ May be gated- can open / close
● Carrier proteins facilitate diffusion of (slightly larger) substances
○ Complementary substance attaches to binding site
○ Protein changes shape to transport substance
Describe how movement across membranes occurs by osmosis
● Water diffuses / moves
● From an area of high to low water potential (ψ) / down a water potential gradient
● Through a partially permeable membrane
● Passive - doesn’t require energy from ATP / respiration (only kinetic energy of substances)
Water potential is …
Water potential is a measure of how likely water molecules are to move out of a solution - pure (distilled) water
has the maximum possible ψ (0 kPA), increasing solute concentration decreases ψ
Describe how movement across membranes occurs by active transport
● Substances move from area of lower to higher concentration / against a concentration gradient
● Requiring hydrolysis of ATP and specific carrier proteins
Describe the role of carrier proteins and the importance of the hydrolysis of
ATP in active transport
1.Complementary substance binds to specific carrier protein
2. ATP binds, hydrolysed into ADP + Pi, releasing energy
3. Carrier protein changes shape, releasing substance on side
of higher concentration
4. Pi released → protein returns to original shape
Describe how movement across membranes occurs by co-transport
● Two different substances bind to and move simultaneously via a
co-transporter protein (type of carrier protein)
● Movement of one substance against its concentration gradient is often
coupled with the movement of another down its concentration gradient
Absorption of sodium ions and glucose (or amino acids) by cells lining the mammalian ileum
1 ● Na+ actively transported from
epithelial cells to blood (by Na +/K+pump)
● Establishing a conc. gradient
of Na+ (higher in lumen than
epithelial cell)
2 ● Na+ enters epithelial cell down
its concentration gradient with
glucose against its
concentration gradient
● Via a co-transporter protein
3 ● Glucose moves down a conc.
gradient into blood via
facilitated diffusio
Describe how surface area, number of channel or carrier proteins and
differences in gradients of concentration or water potential affect the rate of
movement across cell membranes
Describe how surface area, number of channel or carrier proteins and
differences in gradients of concentration or water potential affect the rate of
movement across cell membranes
● Increasing surface area of membrane increases rate of movement
● Increasing number of channel / carrier proteins increases rate of facilitated diffusion / active transport
● Increasing concentration gradient increases rate of simple diffusion
● Increasing concentration gradient increases rate of facilitated diffusion
○ Until number of channel / carrier proteins becomes a limiting factor as all in use / saturated
● Increasing water potential gradient increases rate of osmosis
Explain the adaptations of some specialised cells in relation to the rate of
transport across their internal and external membrane
● Cell membrane folded eg. microvilli in ileum → increase in surface area
● More protein channels / carriers → for facilitated diffusion (or active transport - carrier proteins only)
● Large number of mitochondria → make more ATP by aerobic respiration for active transport
