Cell organelles Flashcards
Mitochondria
-Role is the site of aerobic respiration, so to produce ATP
-Double membrane to control the entry and exit of material, inner is folded to form cristae, providing a large SA for enzymes and proteins
-Matrix is inside, containing enzymes involved in respiration
Endoplasmic reticulum
-A series of membrane folds spreading through the cytoplasm
-Space between the folds is filled with fluid that transports substances
-Rough ER has ribosomes on surface, it folds and processes proteins made at the ribosomes
-Smooth ER has no ribosomes on surface, it synthesises and processes lipids
Lysosomes
These contain digestive enzymes (lysozymes) which digest invading cells
Chloroplasts
-Role is to carry out photosynthesis
-Chloroplast envelope controls the entry and exit of substances (double membrane)
-Inner membrane is the thylakoid membrane which stack to form grana, which are linked by lamellae.
-Photosynthesis occurs in the grana or stroma
Plasma membrane
-Controls the entry and exit of substances into and out of the cell
-Made up of a phospholipid bilayer
Nucleus
-Largest organelle containing DNA
-Surrounded by the nuclear envelope
-Nuclear pores allow the passage of large molecules
-Nucleolus synthesises ribosomes (small dark structure)
-Nucleoplasm is the granular, jelly-like substance making up most of it
Ribosomes
-Very small cytoplasmic granules floating freely in the cytoplasm OR attached to the rough ER
-Sites of protein synthesis
-70S (prokaryotes) or 80S (eukaryotes)
Golgi apparatus
-A stack of membranes making up flattened sacs (cisternae) containing vesicles
-Processes and packages new lipids and proteins
-Also makes lysosomes
Golgi vesicles
-Fluid filled sacs surrounded by a membrane and produced by the golgi apparatus
-Stores lipids and proteins made by it and transports them out the cell
Cell wall
-Provides strength and rigidity
-Made up of cellulose (or chitin in fungi)
Vacuole
-A membrane-bound, fluid filled sac that contains cell sap.
-The membrane is called the tonoplast
-Helps to maintain pressure and keep it rigid
Algal cells
Have the same organelles as plant cells
Fungal cells
Similar to plant cells but have a chitin cell wall (not cellulose) and no chloroplasts as they don’t photosynthesise
What is a virus?
A non-cellular, non-living particle made up of genetic material and protein that can invade living cells. They are much smaller than DNA.
What organelles does a virus have?
-Attachment proteins allow the virus to attach to host cells
-Capsid is a protein coat which transfers the virus genome between cells
-Lipid envelope
-Genetic material
-Enzyme reverse transcriptase
-NO plasma membrane, ribosomes, or cytoplasm
Describe the process of viral replication
-Attachment proteins bind to complementary receptors on host cell membranes
-Therefore each virus can only infect one type of cell.
-They then inject their DNA or RNA into the host cell and use its own ‘machinery’ to replicate the viral particles.
Flagella
Hair like structures which rotate to make prokaryotic cells move
Capsule
Helps to protect prokaryotic cells from attacks by immune cells
Plasmids
-Small loops of DNA
-Contain genes for antibiotic resistance and can be passed between prokaryotes
-Not always present, but some cells have multiple
What is a prokaryote?
Any organism whose DNA is suspended freely in the cytoplasm
What organelles do prokaryotes have?
-Cytoplasm (70S ribosomes)
-Plasma membrane (ATP produced here as no mitochondria)
-Cell wall
-Capsule
-Flagella
-Plasmids
-Circular DNA
Describe the process of binary fission
1) Circular DNA and plasmids replicate
2) The cell gets bigger and DNA loops move to opposite poles of the cell
3) The cytoplasm begins to divide and new cell walls begin to form
4) The cytoplasm divided and 2 daughter cells are made. Each daughter cell has one copy of circular DNA but a variable number of plasmids
What is cell fractionation?
The process where cells are broken up and separated out into their different organelles
What happens before cell fractionation?
-The tissue is placed in a cold, buffered solution of the same water potential as the tissue.
-Cold to reduce enzyme activity that could break down the tissue.
-Buffered so that pH doesn’t fluctuate, which could affect organelle structure and enzymes)
-Same water potential so no shrinking or bursting due to osmotic gain/loss.
What are the 2 stages of cell fractionation?
Homogenation and ultracentrifugation
What is homogenation?
The process where cells are broken up by a homogeniser
Describe the process of homogenation
Organelles are released from the cell and the resultant fluid (homogenate) is then filtered to remove any complete cells and large pieces of debris.
What is ultracentrifugation?
The process where fragments in the filtered homogenate are separated in a centrifuge
Describe the process of ultracentrifugation
1) Tubes of homogenate are spun at low speeds in a centrifuge.
2) The heaviest organelles (nuclei) are forced to the bottom and form a sediment.
3) The fluid at the top (supernatant) is removed, leaving the nuclei sediment to collect.
4) The supernatant is then spun at a faster speed in a different tube and the next heaviest organelles are separated (mitochondria) and forced to the bottom.
5) Process continues like this until the desired organelle is separated and collected.
What is magnification?
How many times larger a sample appears to be compared to its actual size
What is resolution?
The ability to distinguish between 2 separate points.
What are the 3 types of microscope?
-Optical
-Transmission electron (TEM)
-Scanning electron (SEM)
Describe optical microscopes
-Use light to produce an image
-Maximum resolution of 0.2 um (can’t see small organelles)
-Maximum magnification of x1500
-Can see objects in colour due to wavelengths of visible light
-Cheap and easy to use
Describe transmission electron microscopes
-Use electromagnets to focus a beam of electrons which is transmitted through the specimen
-Denser parts absorb more electrons, making them look darker
-Good as they give high resolution images, so internal structures can be seen
-Can only be used on thin specimens
Describe scanning electron microscopes
-They scan a beam of electrons across a specimen, which knocks off electrons which then gather in a cathode ray tube to form an image.
-Images show the surface and can be 3D
-Good as they can be used on thick specimens
-However they do have lower resolution.
