3.2 Cells Flashcards
What is the structure and function of the cell-surface membrane and in which cells can it be found?
Structure:
- Phospholipid bilayer.
Function:
Regulates movement of substances into & out of the cell.
Found in: animal, plant, algal and fungal cells
What is the structure and function of the nucleus and in which cells can it be found?
Structure:
- Double membrane (nuclear envelope) encloses and protects DNA. Outer membrane of envelope is continuous with rer for easy transportation of substances.
- Nuclear pores allow entry & exit of substances.
- Nucleoplasm contains chromatin (during cell division condenses to form chromosomes) and nucleolus (makes RNA & ribosomes).
Function:
Controls all activities within the cell. Contains DNA required for protein synthesis.
Found in: animal, plant, algal and fungal cells
What is the structure and function of mitochondria and in which cells can they be found?
Structure:
- Double membrane isolates respiratory reactions from general cytoplasm (so high conc of enzymes + substrates can be maintained). Inner membrane folds to form cristae (increase SA for attachment of enzymes).
- Matrix (contains enzymes).
- Inner membrane spanned with proteins (allows entry of pyrovic acid + oxygen & exit of ATP + carbon dioxide).
- Contains DNA + ribosomes involved in protein synthesis.
Function:
Site of aerobic respiration whereby ATP is produced.
Found in: animal, plant, algal and fungal cells
What is the structure and function of chloroplasts and in which cells can they be found?
Structure:
- Double membrane isolates photosynthetic reactions from general cytoplasm.
- Stroma contains series of flattened sacs (thylakoid membranes) which can be stacked into grana (increased SA for assembly of chlorophyll + attachment of enzymes).
- Contains DNA + ribosomes involved in nucleic acid & protein synthesis.
- Contains starch grains
Function:
Site of photosynthesis. Absorbs light energy.
Found in: plant and algal cells
What is the structure and function of the Golgi apparatus & Golgi vesicles and in which cells can they be found?
Structure:
- Stack of membrane bound fluid filled flattened sacs (cisternae).
- Vesicles often seen on the edges of the sacs.
- Receives proteins from the ER & modifies them.
- Proteins then packaged into vesicles to be transported.
Golgi body function:
Processes & packages new lipids & proteins. Makes lysosomes.
Golgi vesicles function:
Stores lipids & proteins processed by Golgi body.
Found in: animal, plant, algal and fungal cells
What is the structure and function of lysosomes and in which cells can they be found?
Structure:
- Type of Golgi vesicle.
- Spherical sacs surrounded by single membrane.
- Contain powerful enzymes which digest and break down materials.
Function:
Contains lysozymes used to digest pathogens or worn out cell components.
Found in: animal, plant, algal and fungal cells
What is the structure and function of ribosomes and in which cells can they be found?
Structure:
- Very small organelle that floats freely in cytoplasm or bound to RER.
- Not membrane bound.
- Large & small subunit.
Function:
Site of protein synthesis.
Found in: animal, plant, algal and fungal cells
What is the structure and function of the rough endoplasmic reticulum (rer) and in which cells can it be found?
Structure:
- Series of flattened membrane bound sacs (cisternae) continuous with the nucleur membrane.
- Covered in ribosomes (protein synthesis).
Function:
Folds & processes proteins.
Found in: animal, plant, algal and fungal cells
What is the structure and function of the smooth endoplasmic reticulum (ser) and in which cells can it be found?
Structure:
- Series of flattened membrane bound sacs (cisternae) continuous with the nucleur membrane.
- No ribosomes (involved in making lipids).
Function:
Synthesises & processes lipids.
Found in: animal, plant, algal and fungal cells
What is the structure and function of the cell wall and in which cells can it be found?
Structure:
- Rigid structure.
- Made of cellulose (in plants).
- Made of chitin (in fungi).
Function:
Strengthens & supports cell, prevents them from changing shape.
Found in: plant, algal and fungal cells
What is the structure and function of the cell vacuole and in which cells can it be found?
Structure:
- Surrounding membrane called the tonoplast.
Function:
Contains cell sap to keep cell turgid (maintains pressure inside cell).
Found in: plant cells
How do prokaryotic cells differ from eukaryotic cells?
- They are much smaller
- They have no membrane-bound organelles
- They have smaller ribosomes
- They have no nucleus - instead they have a single circular DNA molecule that is free in the cytoplasm
- They have a cell wall that contains murein (a glycoprotein)
- Some may have one or more plasmids (small loops of DNA)
- Some may have a capsule surrounding the cell (secreted layer to protect against attacking immune cells)
- Some may have one or more flagella (for mobility)
What is the structure of viruses?
- They are are acellular & non-living - invade & reproduce inside host
- They contain genetic material (DNA or RNA)
- They are surrounded by a capsid (protein coat which encloses genome)
- They have attachment proteins (allow virus to attach to host cell)
What is magnification?
What is resolution?
Magnification - how much bigger the image is than the specimen.
Resolution - how well we can distinguish between 2 points close together, resulting in the level of detail observed.
What are the differences between optical microscopes & electron microscopes?
Optical:
- Uses light to form image.
- Max resolution of 0.2 micrometers (wavelength of light is long).
- Max magnification of x1500.
Electron:
- Uses electrons to form image.
- Max resolution of 0.0002 micrometers.
- Max magnification of x1500000.
What is a condenser (found in an optical microscope)?
Gather light from the microscopes light source & concentrate it onto the specimen being viewed.
What are the 2 types of electron microscope?
- Transmission electron microscope (TEM)
- Scanning electron microscope (SEM)
What are the features of TEMs & SEMs?
TEMs:
Work by: Using electromagnets to focus a beam of electrons which is transmitted through the specimen. (Denser parts of the specimen absorb more electrons, making them look darker in the image).
+ Give high resolution images.
- Image viewed is 2D.
- Have to view specimen in vacuum (only non-living specimens can be viewed).
- Can only view very thin specimens.
- Does not show colour.
SEMs
Work by: Scanning a beam of electrons across the specimen which scatters/knocks electrons from the specimens surface. These can then be detected in cathode ray tube to form image.
- Produces lower resolution images than TEMs.
+ Image viewed is 3D.
- Have to view specimen in vacuum (only non-living specimens can be viewed).
+ Can view thicker specimens.
How do you prepare a specimen for viewing in an optical microscope, TEM & SEM?
Optical - use pipette to place small drop of water onto centre of the slide - use tweezers to place thin section of specimen on - add drop of stain - add cover slip
TEM - specimen placed in fixing solution, dehydrated & embedded in resin - sections cut using ultramicrotome into very thin sections
SEM - drying of specimen - coating specimen with conducting material.
What are microscope artefacts and how did the first scientists distinguish between artefacts & organelles?
Things you can see down the microscope that aren’t part of the cell/ specimen you’re looking at. Usually made during the preparation of the specimen and shouldn’t be there.
(Common in electron micrographs as specimens need lots of preparation before viewing).
The first scientists could only distinguish by repeatedly preparing specimens in different ways. If an object could be seen with 1 prep technique & not another it was likely to be an artefact.
What is cell fractionation and what are the steps?
- Homogenisation (breaking up the cells)
- vibrating the cells or grinding them up in a blender
- breaks open plasma membrane & releases organelles into solution
- must be ice-cold (to reduce lytic enzyme activity (produced by bacteria/ viruses - enzymes that would break down cell wall/membrane)), isotonic (same concentration to prevent damage to organelles by osmosis (lysis/bursting)), buffer (maintain pH to reduce denature of enzymes) - Filtration (getting rid of the big bits)
- Homogenised cell solution is filtered through a gauze to separate any large cell debris/tissue debris from the organelles - Ultracentrifugation (separating the organelles)
- cell fragments poured into tube
- put in centrifuge & is spun at low speed
- heaviest organelles (like nuclei) get flung to bottom of tube & form thick sediment at bottom (the pellet)
- the rest stay suspended in fluid above (the supernatant)
- supernatant drained off, poured into another tube & spun at higher speed
- process repeats at higher & higher speeds until all organelles are separated in order of mass (nuclei, mitochondria, lysosomes, E.R, ribosomes) (plant cells: chloroplasts in between nuclei & mitochondria)
How do you calculate total magnification of a microscope?
Magnification of objective lens x Magnification of eyepiece lens
How do you calculate the magnification of an image?
Image size / Actual size
What is the measurement of 1 division of an eyepiece graticule?
Once calibrated with the stage micrometer 1 division is:
25µm at x400
100µm at x100
How do eukaryotic cells divide/replicate?
The cell cycle.
- interphase
- mitosis
- cytokinesis
Describe interphase in detail.
G1 stage - Organelles grow. Duplication of all proteins, organelles & other cell components.
S stage - Chromosomes replicate. Enzymes move along new DNA strands & check copying has been done correctly (check for mutations which could prevent the new cell functioning) + carry out repairs.
G2 stage - Cell keeps growing & proteins needed for cell division are made.
What division stages are there in mitosis?
Prophase, Metaphase, Anaphase, Telophase
(PMAT)
What is the structure of the chromosomes of a cell at the beginning of mitosis?
Chromosomes made of 2 strands joined in the middle by a centromere. The separate strands = chromatids.
The are 2 strands because each chromosome has already made an identical copy during interphase.
When mitosis is over they are 1 strand.
> < - chromosome < - 1 chromatid
Describe what happens to the cell during prophase.
- Chromosomes condense (get shorter & fatter) & are visible
- Centriole divides into 2 & each start moving to opposite ends of cell
- Centrioles forms a network of protein fibres across cell (the spindle)
- Nuclear envelope breaks down & chromosomes lie free in cytoplasm
