Bio lesson 2.4 pdf
Learning Tip of the Day
Visual models simplify complex concepts & relationships. Learning to read them takes practice!
As you examine a figure, ask yourself:
Have I read the legend and section of text where the figure is called out? Do I understand what the words mean?
Are all the parts of the figure at the same scale, or different scales? At one time, or at different times?
Do I understand what the symbols in the figure represent?
Do I understand the use of color?
Lecture 2.4: Non-Enzyme Protein Functions
Proteins can be classified based on their primary cellular role.
Membrane Proteins
Membranes contain proteins that alter their _.
Cell membranes are a _ of different molecules.
Functions of membrane proteins include:
Transporters
Metabolic enzymes
Receptors
Anchors, etc.
Integral (transmembrane) proteins:
These proteins are embedded in the plasma membrane.
Characteristics include:
Located at both the outside and inside of the cell.
Peripheral membrane protein: found on one side of the membrane, covalent interaction.
Amphipathic proteins can integrate into lipid bilayers (meaning these proteins have both hydrophilic and hydrophobic parts).
Amino acids that could potentially cross the bilayer include: F, L, V, P, W, M, A.
Transport Mechanisms
In , a polar molecule moves through a transport protein _ its gradient.
The protein has a pore that is sized to accommodate a specific molecule or ion.
This pore is lined with _ that facilitate transport by forming bonds & interactions with the transported molecule/ion.
Two types: & .
Diffusion
Both processes are (no energy input needed as molecules are moving down a gradient).
Facilitated diffusion is the movement of water through proteins called _.
Depends on concentration of water relative to solute molecules dissolved in the water:
_ : equal solute concentrations
_ : lower solute concentration
_ : higher solute concentration
Aquaporins
Aquaporins are channel proteins with hydrophilic pores for water to pass.
Hypothesis: Aquaporin increases membrane permeability to water.
Methods:
Aquaporin mRNA is injected into an oocyte where it is translated into aquaporin protein.
The oocyte has aquaporins experimentally inserted into the cell membrane.
Results:
Water diffuses into the cell through the aquaporin channels, causing it to swell.
In contrast, oocytes lacking aquaporins do not swell as water cannot diffuse into the cell.
Conclusion: Aquaporin increases the rate of water diffusion across the cell membrane.
Aquaporins play a key role in ___ function and mutations can cause problems.
The tubule network allows reabsorption of ions & nutrients while excluding waste or toxins.
Aquaporins filter small solutes from blood, reabsorbing water and concentrating urine.
Type 2 Diabetes Mellitus
Type 2 Diabetes Mellitus is NOT caused by mutations in aquaporins.
This condition arises when the pancreas does not produce enough insulin and/or the body's cells cannot respond efficiently to insulin.
Insulin is a hormone that signals cells to uptake glucose when blood glucose levels are high.
In Type II Diabetes, glucose remains in the blood, leading to hyperglycemia (high blood glucose).
Channel Proteins
Channel proteins can be regulated by stimuli that alter their _.
Example:
Closed K+ Channel
Open K+ Channel
This involves conformational changes of the protein.
Carrier Proteins
Carrier proteins facilitate diffusion by specifically binding to their target molecule.
Example: Glucose uptake by the glucose transporter process includes:
The glucose carrier protein has a glucose binding site.
Glucose binds to the protein, causing a conformational change.
The altered protein shape releases the glucose.
The carrier protein returns to its original shape, ready to bind another glucose.
Different carrier genes are expressed (transcribed & translated) in different cell types.
Carrier protein activity is regulated by protein _ and _.
Carrier proteins can be relocated to the membrane in response to signaling.
Example scenarios include:
Brain: GLUT3 has binding to glucose.
Liver: GLUT2 has binding to glucose.
The brain consumes 120-130g of glucose per day (~25% of the body’s total glucose consumption) and needs to uptake glucose efficiently.
The brain primarily uses fatty acids for energy and stores excess glucose as glycogen, only uptaking glucose when body cells have sufficient levels.
Translocation Rates
Channels:
Their design allows for rapid transport when speed is a priority.
An open channel can move millions of ions per second, a rate exceeding 1,000 times faster than carrier proteins.
Ideal for rapid changes in concentration, signaling (e.g., nerve signals, water reabsorption in the kidneys).
Carriers:
Mechanism is slower but advantageous for regulated transport.
Determined by binding _ and .
Effective for controlled uptake of essential resources like glucose and amino acids.
Active Transport
transporters utilize energy to move molecules _ their gradient.
This is (not passive): Energy input is required to concentrate a solute on one side of the membrane.
Primary Active Transport
Primary active transporters utilize energy from ATP to move molecules against their gradient.
The structure of ATP includes:
Adenine
Ribose
Phosphate groups
As ATP forms ADP and P, energy is released, resulting in a lower free energy state.
Na+/K+ Pump
The Na+/K+ pump is a primary active transporter that uses energy to transport ions.
Diagram representation:
Outside of cell:
High Na+ concentration, low K+ concentration
Inside of cell:
High K+ concentration, low Na+ concentration
Process includes the following steps:
Three Na+ and one ATP bind to the protein "pump."
Hydrolysis of ATP releases ADP and phosphorylates an amino acid in the pump protein.
The shape change results in the release of Na+ ions outside the cell and allows two K+ ions to enter the pump.
Two K+ ions bind to the pump.
Dephosphorylation of the pump releases P₁, resulting in the release of two K+ ions into the cell interior and returning the pump to its original form.
Secondary Active Transport
Secondary active transporters use the energy of an existing gradient to transport molecules "uphill".
Example of Transporters in the Intestine
Multiple transporters are utilized in the intestine for glucose uptake into the blood, demonstrated as follows:
Low [Na+], high [glucose]
High [Na+], low [glucose]
Drug Targets
Active transporters are common drug targets. Examples include:
Prilosec: Blocks stomach H+ pumps.
Zoloft: Blocks serotonin transporters.
Cocaine: Blocks dopamine transporters.