Cells Flashcards
Cytoplasm (Or cytosol)
Contains enzymes for metabolic reactions
Also contains amino acids, salts and sugars
Nucleus
Contains hereditary material
Produces RNA (mRNA, tRNA, rRNA)
Controls the activities of the cell
Contains nuclear pores to allow substances (mostly mRNA) in and out of the cell
Mitochondria
Site of aerobic respiration
ATP formed
Double membrane
Inner membrane = highly folded = cristae
This increases surface area to fit more enzymes so faster respiration
Inside cristae there is a fluid called matrix - Contains DNA and ribosomes
Ribosome
Protein Synthesis
Smallest organelle in the cytoplasm
80S in eukaryotic and 70S in prokaryotic
Endoplasmic Reticulum
Join to the nuclear envelope, layers of flattened sacs called cisternae
Rough endoplasmic reticulum
Encrusted with ribosomes that synthesise proteins
Smooth endoplasmic reticulum
No ribosomes
Synthesises stores and transports lipids and carbohydrates
Gulgi apparatus/vesicles
Multiple flattened sacs form cristanae
Products from ER pass through it
Modifies substances and packages them into golgi vesicles
Also make lysosomes
Finished products transported to cell surface in golgi vesicles where they fuse with the membrane and are released
Lysosomes
Produced by the golgi apparatus
Sacs surrounded by a single membrance
Contain hydrolytic enzymes (enzymes that break down biological molecules)
Destroy unwanted chemical, worn out organelles, engulfed viruses/bacteria, dead cells (autolysis)
Products then recycled to synthesise new substances
Chloroplasts
Double membrane which is high selective
A thylakoid is a single disc containing chlorophyll
A granum is stacks of thylakoids
Lamella connect granum together
Stoma
Fluid filled matrix where sugars are synthesised during photosynthesis. Enzymes and starch grains often found here
Vacuole
Contains a solution of salt, sugar and amino acids (makes cells turgid)
What is the cytoplasm of a bacterial cell made of
Peptidoglycan and murein
Light microscope
Limited by x1500
Allows individual cells and some larger structures such as the nucleus to be observed but no smaller structures
Resolution is approximately 0.2 micrometres
Why do light microscopes have a low resolution
Light microscopes have a long wavelength of light
Electrons are used to increase resolution as they have much shorter wavelength
How an electron microscope works
Specimen must be thin for electrons to pass through
Electron gun fires electrons
electromagnets focus electrons towards specimen
Fluorescent screen - detects numbers and scattering of electrons and produces an image
Advantages of light microscope
Cheaper
Produce coloured images - add stains to specimen
Easy to use
Portable
Disadvantages of a light microscope
Lower resolution
Lower magnification
Advantages of electron microscope
Higher resolution
Higher magnification
Disadvantages of a electron microscope
Expensive
Specimen has to be dead which requires a vaccum
Black and white images
Not portable
Difficult to use
Artefacts can be produced (false images)
Transmission electron microscope (TEM)
An electron gun produces and fires electrons which focuses on the specimen by a electromagnet
Beam passes through a thin specimen, part of it absorbs the electrons and the others allow the electrons to pass through, forming a bright image
The resolving power is 0.1nm
Produces a micrograph
Disadvantages of a Transmission Electron Microscope (TEM)
Vacum - living organisms cannot be observed
Staining required despite image not being in colour
Specimen must be extremely thin
Image may contain artefacts
Scanning Electron Microscope (SEM)
Directs/fires a beam of electrons on to the surface of the specimen rather than penetrating it
Beam passed back and forth in a regular pattern, electrons are scattered by the specimen
Produces a 3D image through computer analysis
Disadvantages are the same as the TEM however the specimen does not need to be thin which is an advantage
The resolving power is 20nm
Cell fractionation and Ultracentrifugation - Homogenisation
Homogenisation is the breaking up of cells
The sample must be;
Ice-cold to reduce the activity of enzymes
Isotonic (same water potential as the cells) to prevent water moving into the cells via osmosis
Buffered to prevent enzymes from being degraded
The solution is then homogenised using a homogeniser which is a blender like machine which grinds up the cells
This breaks the plasma membrane of the cells and releases the organelles into a solution called the homogenete
Cell fractionation and ultracentrifugation - filtration
The homogenate is filtered to separate out large cell debris
Cell fractionation and Ultracentrifugation - Ultracentrifugation
Filtrate placed in a tube and then the tube is placed in a centrifuge. (a centrifuge is a machine that seperates materials by spinning)
The filtrate is first spun at low speed causing heaviest organelles ie nucleus to settle at the bottom as a pellet
The rest of the organelles stay suspended in the solution above (supernatent)
The supernatent is drained off and placed at another tube, which is spun at higher speed
Once again however organelles (mitochondria) settle at bottom forming another supernatent
