Lec 7 and 8: Plasma Membrane, Transport and Organelles Flashcards
what are the functions of the plasma membrane?
- It regulates what enters and exits the cell, altering pH and charge
- Is involved with cell recognition
- Plays a major role in cell signalling e.g. from hormones
- Has enzymatic functions
- Aids in cell linking and cross-talk
*NOTE* image of plasma membrane
what does the lipid bilayer consist of?
- Phospholipids (75%)
- Cholesterol (20%)
- Polar Glycolipids in the external layer (5%)
what is the role of cholestrol in the plasma membrane?
- Cholesterol immobilises the first few hydrocarbon groups of the phospholipids molecules.
- drecreases permeability to small water-soluble molecules
why is fluidity important for the plasma membrane?
•allows the movement of membrane components required for cell processes and formation of cellular junctions
what is the glycocalyx?
•glycoprotein’s containing covalently bonded to oligosaccharides
what are roles of membrane proteins?
- Required for detection of ‘self’ in immunity
- Aids in cell- cell adhesion
- Makes RBCs slippery and protects the GI from drying out
If a membrane was depleted of cholesterol what would happen to the membranes structure?
Why do you think intracytoplasmic sperm injection doesn’t rupture the target egg cell?
what is the plasma membrane selectively permeable to?
•The lipid bilayer is permeable to non-polar molecules such as O2, CO2 and hormones
what is the plasma membrane impermeable to?
Ions and large molecules such as Na+ and glucose.
They need trans-membrane channel and carrier proteins
what is the plasma membrane slightly permeable to?
small uncharged polar molecules such as water
what is the importance of membrane permeablility?
- allows cells to build concentration gradients
e. g. O2and Na+ are more concentrated in the extracellular fluid: the opposite is true for K+ & CO2 - pH can be regulated
- membrane potential is created from electrical gradients
the inside of the cell is more positive or negative?
positve
what is passive transport and what are the different types?
passive transport = No cellular energy is used as substances move down their own concentration gradient.
types of passive transport:
– 1. Diffusion through lipid bilayer
– 2. Channel mediated facilitated diffusion
– 3. Carrier mediated facilitated diffusion
what are the two types of diffusion?
channel mediated diffusion: gated, timed or signal regulated
carrier mediated diffusion: subject to transport, maximum and saturation
How can insulin speed up the entry of glucose into the cell?
insulin facilitates the diffusion of glucose into cells
by up-regulating glucose transporters via its receptors
what is osmosis?
diffusion of water through a semi-permeable membrane.
diffusion through the lipid bilayer occurs through specific transmembrane protein channels called aquaporins
what is the difference between hypertonic, isotonic and hypotonic solutions?
In what clinical condition is a hypertonic solution used?
hypertonic: high water potential so water moves out of cells
isotonic: water potential is maintained so no net movement of water molecules
hypotonic: low water potential in cells so water moves into the cells
Infusion of hypertonic solution to relieve cerebral edema
what is active transport? what does it help to maintain?
- process that uses energy from the hydrolysis of ATP
- used to transport ions against their conc gradient
helps to maintain tonicity, volume and charge
what are the two types of active transport?
Primary active transport (uses energy from the hydrolysis of ATP)
Secondary active transport (uses energy stored by an ionic concentration gradient)
what is primary active transport?
give an example
- Movement against a concentration gradient (mainly ions)
- ATP changes the shape of the carrier protein, pumping the substance across
- Most common example is sodium-potassium pump
what is secondary active transport (co-transport)?
where transporter protein couples the movement of an ion (Na+ or H+) down it electrochemical gradient
to the uphill movement another molecule or ion against a concentration/electrochemical gradient.
what is the difference between symport and antiport?
- Symport is where the molecules travel in the same direction (used for Ca2+ regulation and H+ regulation)
- Antiport is where they go in opposite directions
what is transcytosis?
- Combination of endo and exocytosis
- Substances are passed through a cell
- Is common in endothelial cells which line the blood vessels
what is vesicular transport used for?
- endocytosis (bringing substances into the cell)
- exocytosis (expelling from the cell, in secretory cells and nerve cells)
- inter-organelle transport
what are the 3 types of endocytosis?
- Receptor mediated endocytosis
- Phagocytosis and
- Pinocytosis
what are the steps involve in receptor mediated endocytosis?
Process used for transporting LDL, vitamins and hormones
- Binding
- Vesicle formation
- Unseating
- Fusion with endosome
- Recycling of receptor
- Degradadtion in lysosomes
what is clathrin?
•protein for enriching membrane domains
what is phagocytosis?
where large particles (worn out cells and bacteria) are englufed
carried out by macrophages and neutrophils
what are the steps involved in phagocytosis?
- chemotaxis and adheremce of microbe to phagocyte
- ingestiion of microbe of phagocyte
- formation of phagosome
- fusion of the phagosome with a lysosome to form a phagolysosome
- digestion of ingestion microbe by enzymes
- formation of residual body containign indigestible material
- discharge of waste materials
what is pinocytosis?
ingestion of droplets of extracellular fluid into a cell
without the use of receptors
It is non selective and occurs most in absorptive cells in the intestines and kidneys
what are the types of cell junctions (5)?
Tight junctions
Adherens junctions
Desmosomes
Hemidesmosomes
gap junctios
what do tight junctions do?
•prevent movement of substances
e.g cells lining the ddigestive tract
what is the function of ahdereing junctions?
maintain cellular position and resist seperation in contracile acitivities
made up of plaque which attaches to the membrane proteins and the microfilaments of the cytoskeleton
what are desomosomes and hemidesmosomes?
what is their function?
- anchoring junctions held together by linker protein filaments called cadherins or integrins extending from button like thickenings called plaques.
- Distributes tension and prevents tearing.
e.g. skin and heart muscle
what are gap junctions?
what is their function?
hollow cylinders called connexons made of trans membrane proteins
they create gaps that connect animal cells
found in heart and smooth muscle tissue
what are the two components within a cytoplasm?
- The cytosol (intracellular fluid)
- The organelles (specialised structure which co-operate to maintain homeostasis)
what does the cyosol contain and what is it’s function?
- Contains dissolved ions, glucose, amino acids, ATP, lipids and waste products
- Is the site for a wide range of enzymatically controlled reactions
what is the cytoskeleton?
a network of protein filaments extending throughout the cytoplasm
what are the three main types of cytoskeleton?
- Microfilaments
- Intermediate filaments and
- Microtubules
In the cytoskeleton what is the micro filament and what is does it do?
polymers of the proteins actin and myosin
that surround the edge of the cell
help generate movement, provide support needed for strength and shape
and create microvilli
In the cytoskeleton what are the intermediate filaments? what is their function?
a family of proteins such as keratin, vimentin and lamin
found in the cell subject to mechanical stress
that help stabilise the position of the organelles
In the cytoskeleton what are microtubules?
what is their function?
long unbranched hollow tubules made from tubulin
that form the centrosome
help with strength, shape and movement of organelles such as vesicles during division
provide structure to flagella
what is the centrosome?
what is the function of the centrosome?
consist of 2 centrioles which are cylindrical structures composed of a circle of nine clusters of microtubule triplets, both at right angles to each other
for growth of mitotic spindle during cell division
what is the difference in the centrosome in a cell that is is/is not undergoing division?
- When a cell is not undergoing division, a single centrosome is present.
- However, when the cell does begin to divide the centrosome replicates early in the process.
what are cillia and flagella?
what are their function?
motile projections on cell surface made from microtubules
transport of fluid along cell surface
what is each cilium anchored to?
how does smoking affecting cilia?
each cilium id anchored to the basal body
smoking destroys the cilia
causing a persistent cough to remove the build up mucus, dust and bacteria
causing female smokers to have an increase risk of an ectopic pregnancy
*Note* difference between cilia and flagella
similar in structure but flagella are much longer and often only one is found on a cell
what is the Endoplasmic reticulum?
•ER is a network of membranes in the form of flattened sacs and tubules extending from the nuclear envelope into the cytoplasm
*NOTE* Rough ER
Rough ER contains ribosomes attached
Proteins made by the ribosomes enter the ER space for processing and sorting
*NOTE* smooth ER
- Extends from the rough ER
- Contains no ribosomes but has a greater range of enzymes, making its functions more diverse
- Synthesizes fatty acids and steroids such as estrogens and testosterone
- In the liver it helps release glucose from gluc-6-p and detoxify lipid soluble drugs such as alcohol and pesticides
- Stores Ca2+ ions in muscle
what is the golgi complex
3-20 membranous cisternae(sac like structures) with bulging edges arranged in a stack.
The convex entry/cis face faces the ER and the concave exit/trans face faces the plasma membrane.
Sacs between are called medial cisternae
*trans=transports proteins away*
explain the processing and packaging done by the golgi
- Proteins surrounded by ER membrane and transported through the cell
- Transport vesicles move to entry face
- Fusion of several vesicles crates the entry face and releases proteins
- Proteins are modified and move into medial cisternae, then either taken back to the entry face or to the exit face
- Within the exit face proteins are modified and packaged
6-9. Proteins sent to their destinations
what is the function of a lysosome?
•Digestion of substances entering the cell, worn out organelles (autophagy) and entire cells (autolysis)
what is the result of the absence of the lysosomal enzyme Hex A?
absence Hex A causes Tay- Sachs disease
- Hex A normally breaks down a glycolipid prevalent in nerve cells
- with its absence the glycolipid builds up destroying nerve cell function
- patient suffers from seizures and muscle rigidity and become blind
what are peroxisomes?
how are they different to lysosomes?
organelles that contain enzyme oxidases that metabolise amino acids, fatty acids and oxidise alcohol
contain enzyme catalase for protection against hydrogen peroxide
smaller than lysosomes
what are three peroxisomal disorders?
- Zellweger syndrome (ZS)
- neonatal adrenoleukodystrophy (NALD)
- rhizomelic chondrodysplasia punctata (RCDP),
how proteasomes different from lysosomes?
proteasomes contain protease enzymes that degrade cytosolic proteins (uneeded proteins)
and are involved in negative feedback
where as lysosomes degrade proteins delivered in vesicles
*NOTE* mitochondria
*NOTE* nucleus
