Membrane Structure And Function 2 Flashcards
What is the major function of the plasma membrane?
Barrier, transport, signal transduction
What is the major function of the mitochondrial inner membrane?
Energy transduction
What is the major function of the mitochondrial outer membrane?
Physical barrier
What is the major function of the rough ER membrane?
Translation and protein processing
What is the major function of the smooth ER membrane?
Synthesis of complex lipids
What is the major function of the Golgi membrane?
Post-translational modification and processing for secretion
What is the major function of the nuclear membrane?
Attachment of chromatin
What is the major function of the lysosomes membrane?
Hydrolytic enzymes
What is the major function of the peroxisome membrane?
Fatty acid oxidation
What does the ratio of the protein: lipid depend on?
The type of membrane and its function
Why is the lipid content of the myelin so high?
Insulator
What are the two membranes that have similar functions and a 50:50 ratio of lipid to protein?
Erythrocyte and hepatocytes
What are the membrane ratios in the mitochondrial membranes?
Outer = 50:50 cuz barrier role Inner = 75:25 protein: lipid due to electrons used in ATP production
In a purely phospholipid membrane what is the permeability of lipid soluble molecules?
Move either way
Name some lipid soluble molecules
Hydrophobic, small uncharged or polar molecules
How do lipid soluble molecules move through the phospholipid membrane?
Simple diffusion from high conc to low conc
Name the passive non mediated mechanism
Simple diffusion
Name the passive carrier mediated mechanism
Uniporters
What is a co transport symporter?
Molecules that are generally transported in the same direction
What does a cotransport symporter need to work?
Both molecules
What is a cotransport antiPorter?
Molecules move in opposite directions
What does a small amount of solute do to the rate of solute transport in carrier mediated transport?
A huge increase in transport rate
What does a small amount of solute do to the rate of solute transport in simple diffusion?
It is a straight line
What happens to carrier mediated when there is an excess of solute?
It plateaus because it gets saturated
What happens to simple diffusion when there is an excess of solute?
The rate of solute transfer keeps increasing
What is the Kt?
Affinity of the transporter for the substrate
Which of simple diffusion and carrier mediated movement is driven by concentration gradient?
Both
Which of simple diffusion and carrier mediated movement needs energy?
Neither
Which of simple diffusion and carrier mediated movement needs specificity?
Carrier mediated
Which of simple diffusion and carrier mediated movement is slow and which is fast?
Simple diffusion is slow, carrier mediated is fast
Which of simple diffusion and carrier mediated movement is capacity limited?
Carrier mediated
What is the resting circulating concentration of glucose?
4mM
What is the circulating concentration of glucose after a meal?
10-15mM
Where are GLUT 1 and 3 found?
In all mammalian tissues
What is the kt of GLUT 1 and 3?
1mM
When are GLUT 1 and 3 fully active?
At resting concentration
What GLUT protein is activated at High glucose concentrations?
GLUT 2
Where is GLUT2 found?
Liver and pancreatic beta cells
What is the kt of GLUT 2?
15-20 mM
What do liver cells do?
Take glucose up and store as glycogen or fatty acids
What do pancreatic beat cells do?
Regulate the production of insulin
What do GLUT 4 and 5 do?
Maintain the glucose levels in normal cells so they can function
Where is GLUT 4 found, and what is its kt?
Muscle and adipose tissue- kt = 5mM
Where is GLUT 5 found?
Small intestine
How do carrier mediated transporters function?
Binds to the transporter, which undergoes a series of conformational changes allowing the molecule to move across the membrane. The transporter then returns to its original confirmation
How is the gradient of glucose maintained?
Glucose -> G6P
Which glucose isoform is transported?
D-glucose
How can you increase the transport of glucose?
Increasing the number of transporters on the cell surface
How are GLUT4 transporters increased on muscle and adipocytes?
Insulin
What is the conc of Na+ Ions outside the cell?
143mM
What is the Na+ conc inside the cell?
14mM
What does the active transport of Na+ require?
An integral membrane protein
What does SGLUT1 do?
Transports glucose when sodium is present
What enzyme is involved in the Na+/K+ cotransport mechanism?
NA+ - K+ ATPase
What is SGLUT1?
A Na+-glucose symporter
How is cellular asymmetry in cells maintained?
The plasma membrane of adjacent cells coming together to form tight junctions
What do tight junctions prevent?
The redistribution of transport proteins around the cell?
What is rehydration therapy?
Therapy to combat the loss of water, electrolytes and food nutrients during bouts of diarrhoea
What is rehydration therapy made of?
1L water, 8tsp sugar and 1tsp salt
What does rehydration therapy do?
Means the sodium and glucose is absorbed into the gut and the glucose can be used as an energy source. Sodium also draws in water to rehydrate the individual
What is compartmentalisation and what does it enable?
Intracellular membranes create local environments to separate reactions. It enables electrochemical gradients to be established
What does the inner mitochondrial membrane being very impermeable allow?
The concentration gradient of ATP to fall
What are the lysosomes full of, and what pH do they work best at?
Hydrolytic enzymes work best at pH 4 or less
What is the cytosolic pH?
7.2
How do lysosomes maintain their low pH?
Have a proton pump which pumps H+ into the lumen
What does the lysosomal proton pump require, and what does it mean?
Requires the hydrolysis of ATP but means the activities of the enzymes can be maximised
What are peroxisomes important for?
The breakdown of long chain fatty acids
How many enzymes are present within peroxisomes?
Over 50
What is the internal pH of peroxisomes?
6.5-7.1
How is a protein directed towards a specific organelle?
Signal sequences that target them to specific organelles
How many amino acids long are the protein signal sequences?
2-3 amino acids
How do you prove protein direction?
Tag a cytosolic protein with a fluorescent marker.
Add a small nuclear localising sequence to it
It is then not seen in the cytoplasm but in the nucleus
What happens if you add a carbohydrate signal to a protein?
Protein is made, post translationally modified to add a mannose signal. The mannose is then phosphorylated, which directs the hydrolytic enzymes to the lysosome
What happens if the protein responsible for the phosphorylation of mannose is absent?
This particular enzymes will not appear in the lysosome but will be secreted into the cytoplasm, so the substrate will accumulate in the lysosome
What does I- cell disease do?
Leads to cellular disfunction
What happens if there is I-cell disease?
Significant neurological impairment
