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:
● Selectively permeable → enables control of movement of substances in / out of cell
● Molecules / receptors / antigens on surface → allow cell recognition / signalling
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.
- 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 for energy release.
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) - also contains starch granules & lipid droplets.
- Lamella - thylakoid linking grana.
- Contains DNA + ribosomes involved in nucleic acid & protein synthesis.
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 (small membrane sacs).
- Receives proteins & lipids from the ER & modifies them.
- Proteins/lipids then packaged into vesicles to be transported.
Golgi body function:
Processes & packages new lipids & proteins. Makes lysosomes.
Golgi vesicles function:
Transports 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:
Releases lysozymes used to digest/break down 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 (ribosomal RNA and protein).
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 or bursting under pressure due to osmosis.
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 (nucleic acids))
- They have attachment proteins (allow virus to attach to host cell)
What is magnification?
What is 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
What are the differences between optical microscopes & electron microscopes?
Optical:
- Uses light to form image.
- Low resolution (wavelength of light is long).
- Max magnification of x1500.
Electron:
- Uses electrons to form image.
- High resolution.
- Max magnification of x1000000.
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.
+ Can see internal structures of organelles & ribosomes.
- 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.
- Complex preparation so artefacts often present.
SEMs
Work by: Using electromagnets to deflect/bounce electrons off 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.
- Complex preparation so artefacts often present.
- Does not show colour.
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
Describe how the size of an object viewed with an optical microscope can be measured.
Once calibrated with the stage micrometer 1 division is:
25µm at x400
100µm at x100
- 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
How do eukaryotic cells divide/replicate?
The cell cycle.
- interphase
- mitosis
- cytokinesis
Describe the stages of the cell cycle in eukaryotic cells.
- Interphase
● (S phase) DNA replicates semi-conservatively
- Leading to 2 chromatids (identical copies) joined at a centromere
● (G1/G2) number of organelles & volume of cytoplasm increases, protein synthesis - Mitosis
● Nucleus divides
● To produce 2 nuclei with identical copies of DNA produced by parent cell - Cytokinesis
● Cytoplasm and cell membrane (normally) divide
● To form 2 new genetically identical daughter cells
