What is the size of a water molecule ?
(1/1000 000 th of a mm!)
What is the plasma membrane ?
- A semi-permeable barrier that defines the outer perimeter of the cell
- Composed of lipids and proteins
- The membrane is dynamic, selective, active and fluid
What does amphipathic mean?
A molecule that contains both hydophillic and hydrophobic regions e.g. The phospholipid tail end contais isoluble fatty acids, and the head end is a hydrophillic charged phosphate head.
N.B The plasma membrane contains a bilayer of phospholipids.
What is the Glycocalyx ?
The sugar coat on the outer surface of the outer leaflet of the plasma membrane.
It aids in the attachment of some cells, facilitates cell recognition and helps bind APC's to the cell surface.
What is the differece between extrinsic and intrinsic proteins ?
- Extrinsic or peripheral proteins are associated with the outside of the membrane
- Itrinsic or integral proteins may be found spanning the plasma membrane
How do substaces cross the Eukaryotic plasma membrane ?
(Name 3 ways)
- Simple diffusion
- Carrier-mediated transport
- Endo/Exo - cytosis
Explain simple diffusion ?
Spontaeous movement of a substance from an area of high concentration to an area of low concentration.
What would happen if an erythrocyte was placed in a Hypertonic solution ?
The fluid bathing the erythrocyte contains a high level of solute relative to the cytplasm, therefore water would diffuse out of the cell, causing the cell to shrivel (Crenation).
What would happen to an erythrocyte placed in a Hypotonic solution ?
Here the fluid surrounding the cell has a low level of solute compared to the cytoplasm, therefore water would diffuse into the cell causing it to swell and possibly rupture (lyse).
Name two carrier-mediated transport systems ? What would bind to them ?
- Facilitated Diffusion - E.g. Ion channels transported down an electrochemical gradient
- Active transport - E.g. Uses ATP to transport solutes against their concentration gradiets e.g. Na+, K+. Also transports amino acids, sugars and other solutes
What is Endocytosis ?
The process by which the cell membrane invaginates, pinches off and is released intra-cellularly.
For a solid particle this is known as Phagocytosis.
For a fluid this is known as Pinocytosis.
Explain the use of Clathrin-Coated Vesicles ?
They are found in all cells, and are used to endocytose ligands E.g. LDL's, trasferrin, growth factors and antibodies.
They form areas in the plasma membrane called clathrin coated pits.
What is a Caveolae ?
The most commonly seen, non-clathrin coated plasma membrane buds on the surface of most cells.
Explain Exocytosis ?
The cell directs an intracellular vesicle to fuse with the plasma membrane, thus releasing its contents to the exterior.
(E.g. Neurotransmitters, pancreatic enzymes, cell membrane proteins, lipids etc...)
What are SNARE proteins and what do they do ?
They are found in Porosomes where proteins dock in the process of secretion and fusion. They mediate vesicle fusion through full fusion or open and close exocytosis.
Define the Cytoplasm ?
The interior of the cell.
This includes the Cytosol, Cytoskeleton, and the membrane-bound Organelles.
How does transport occur in the Cytoplasm ?
Cyclosis - The circular motion of Cytoplasm around the cell.
What is the Cytosol ?
The solution which bathes the Organelles and contains numerous solutes E.g. Amino acids, sugars, proteins etc...
What is the Cytoskeleton ?
It extends throughout the entire cell, and maintains the shape of the cell. It also has a function in extracellular transportation.
Explain Cellular adhesion ?
The Cytoskeleton makes extracellular complexes with other proteins forming a matrix so that cells can 'Stick together'.
What are the components of the Cytoskeleton ?
In increasing size:
What is the role of Microfilaments in the Cytoskeleton ?
They are also known as Actin filaments, and are important in cell movement and contraction.
They squeeze the membrane together in Phagocytosis and Cytokinesis. They are also important for muscle contraction and microvilli movement.
What is the role of the intermediate filaments and microtubules of the Cytoskeleton ?
They extend along the axons and dendrites of neurons to enable organelles or protein particles to shuttles to/from the cell body.
They also form:
The core of Cillia and Flagella
The mitotic spindles
What 3 things do Microtubules form ?
- The core of Cillia and Flagella
- The Mitotic spindles
What is a Flagellum ?
An Organelle of locomotion found in sperm and bacteria
What are Cillia ?
Hair-like, vibrating organelles which can be used to move particles along the surface of the cell.
E.g. Fallopian tubes
What is a basal body ?
It is found at the base of the Flagella and Cillia, two centrioles are found at right angles to each other.
What are Microvilli ?
Regularly arranged, finger-like projections with a core of Cytoplasm.
They are commonly found in the small intestine where they help to increase the absorptive and digestive surfaces (aka the brush border).
What are Mitochondria ?
The power-house of the cell, they produce ATP in aerobic respiration and are numerous in muscle cells. They have their own DNA and ribosomes and replicate independently from Eukaryotic cells.
N.B. Most proteins used in Mitochondria are coded by nuclear DNA, not mitochondrial DNA.
What is the role of the Mitochondria in respiration ?
The inner membrane has shelf like folds called Cristae. The matrix contains ezymes for the Krebs cycle and circular DNA.