2# Debra Flashcards
Why must all cells have a plasma membrane?
Phosphate membrane will regulate what moves into and out of the cell
Identity
Responds to signals
Why do we say that membranes are semipermeable and why is this important?
semi permeable membrane: membrane determines what goes into and out of the cell
Important in regulating the internal contents of a cell
Why do phospholipids form bilayers when mixed with water?
phospholipids
G 1. Phosphate (hydrophilic/charged)
2. Fatty acid (hydrophobic/not charged) 3. Fatty acid
middle of the membrane is hydrophobic and very fatty
Why must membranes be fluid to function?
Membranes are fluid in order to be flexible
Proteins in the membrane can change position
What are 3 methods cells use to adjust membrane fluidity?
- Temperature: alter the melting temperature of fatty acids
* By adding more unsaturated fatty acids- fluidity increase* - Change the properties of the polar head groups
- Add chemicals to the bilayer
* add cholesterol = decrease fluidy*
What does amphipathic mean?
Interact with hydrophilic molecules and hydrophobic molecules
What determines what can move across membrane on its own or not?
middle of the membrane is hydrophobic and very fatty
deciding what crosses
What sorts of molecules can pass through lipid bilayer membranes?
Small non polars (fatty)
Small uncharged polar molecules
Gases - CO2, O2, N2
Ex: steroids (hydrophobic) will go through
Why do cells need integral membrane proteins ?
Integral membrane protein allows polar molecules to cross the membrane
What is the general model for the structure of biological membranes?
Carbohydrates: used for cell identity
Eukaryotic Cell
Cholesterol in fatty acids because hydrophobic
diagram
What keeps integral membrane proteins from leaving the membrane?
Integral proteins remain in place due to hydrophobic interactions in the middle of the membrane and hydrophilic interactions on the outside and inside of the membrane
How do we know that proteins can diffuse within membranes?
Proteins can change position within a membrane
Experiment by Eddin and Frye
- fused human and mouse cells
- after 40 minutes, proteins were dispersed through hybrid cell
How can proteins form holes through membranes?
Several different membrane-spanning domains aggregate amino acids line the hole
Hydrophilic amino acids line the pore so polar molecules can be moved across the membrane
What is special about the structure of the plasma membrane, and what sorts of proteins do you find in it and name 3 function of those proteins?
Lipid bilayer forms fluid, semipermeable barrier
Proteins embedded in the membrane are free to move with the membrane, but they cannot get out
Trans(across)membrane (integral) proteins: proteins in the membrane
Peripheral proteins: inside edge or outside of the membrane
Glycolipid = sugar attached to a phosphate head Glycoprotein = attached to protein
Glycocalyx composed of glycoprotein (carbohydrate attached to protein) and glycolipid (carbohydrate attached to phospholipid) on only CELL SURFACE
USED FOR CELL IDENTIFICATION
Attached to cytoskeleton by supporting fibers
Proteins form transport channels
Some proteins are enzymes
Cell surface receptors
What are the functions of the plasma membrane?
Passing water Passing bulk materials Selective transport of molecules Receiving and transmitting information Express cell identity Physical connections with other cells
What is osmosis and why does it occur?
Osmosis-diffusion of water across a semipermeable membrane to equalize water connection on either side
Water will move from a hypoosmotic solution to a hyperosmotic solution
What kinds of cells want to be isosmotic, and what kinds want to be hyperosmotic?
Cells without cell walls want to be isosmotic with their environment
Ex: RBC
In cell: 0.9% water out: 0.9% water
Cells stay same size because same amount of water goes in and out
Cells without cell walls
Animal cells(ex)
Any cell with cell wall Plant cells(ex) want to be hyperosmotic to their environment Plant cells(ex) want to be in a hypoosmotic environment so water enters cell
Terms for comparing 2 solutions:
- definition
- what happens to cell
- what cell want it
- isosmotic: two solutions have the same concentration of water and solute; equal amounts of water move into and out of the cell; cell size stays the same; animal cells want this
- hyperosmotic solution: solution with less water and more solute than the solution you are comparing it to
- hypoosmotic solution: solution with more water and less solute than the solution you are comparing it to
Solution is made of…
Solvent: part of solution in greater amount (water)
Solute: that which is dissolved in the solvent; lesser amount than solvent (lemonade crystals)
Why do cells shrink when placed in a hyperosmotic solution?
Example
Hyperosmotic solution: more water in cell than outside so water will leave the cell and cell will shrink
Lab: plasmolysis of Elodea
Why do red blood cells explode when you place them in distilled water?
RBC in Distilled water:
cell is hyperosmotic environment
environment is hypoosmotic to cell
What is “turgor pressure” and what is it used for?
Turgor pressure will result when plant cells are in hypoosmotic environment
Pressure applied to cell wall of plant cell makes the wall stiff
Plant stands up
How is bulk transport accomplished?
Bulk transport is the use of membrane vesicles to transport large particles out of cell or into cell
What is the difference between endocytosis and exocytosis?
Endo = inside/within Exo = outside
Endocytosis: cell brings particles in
Exocytosis: cell gets rid of particles
What is the difference between phagocytosis and pinocytosis?
If a cell does phagocytosis, particles (solids) are brought into the cell (with other stuff out there too)
If a cell does pinocytosis, it will take liquids in (with other stuff out there too) from the environment
pina colada liquid
There are two types of endocytosis:
phagocytosis
pinocytosis
what doe exocytosis mean?
removing something from cell
What is “receptor-mediated endocytosis”?
How do they work?
Where are they located?
Bringing something into the cell
Receptor will select what is brought in
More specific
- receptors bind certain molecules, the molecules they want to bring in
- receptors are located in “coated pits”; once enough molecules attach to the receptors, vesicle will form and it will move into the cell
diagram
What are the differences between bulk transport and selective transport?
Bulk transport:
Requires a lot of energy
Uses membrane vesicles
Non-selective- takes up “whatever’s out there” in the environment”
Selective Transport:
Uses integral membrane protein to transport specific molecules across the membrane
Saves energy
Allows specificity
What is “selective transport” and what substances do cells move by selective transport?
This is how ions, glucose, small polar molecules like amino acids and nucleotides pass through
How do aquaporins prevent the passage of molecules other than water?
Specialized channels for water enhances the rate of water flow through a membrane, but do not alter the direction of water movement
Very narrow channels with positive charges in the middle that repel + and stop - ions from crossing
How can ion channels tell the difference between one type of ion and another?
They can tell the difference between ions based on the size and charge of the ion
How are ion channels regulated?
Water-filled pores through which SPECIFIC ions flow
- Driving force will be the concentration gradient
- Regulation is by opening and closing the channels
What are the differences [4] between ion channels and facilitated diffusion?
What is the same?
Ion channels:
Pore within integral-membrane protein
Driving force is he concentration gradient
Specific
Non-saturable - if the channel is open, ions are free to move; if the channel is closed, ions cannot move
Facilitated diffusion:
Facilitated = helper Diffusion = no energy / high concentration to low concentration
Receptor protein in the membrane which binds the molecule to be transported and carries it through the membrane
Driving force is concentration gradient
Specific (carries across)
Saturable (time limit on how fast it can take the protein and move it on another side)
BOTH CASES THEY MOVE SUBSTANCES DOWN A CONCENTRATION GRADIENT = no energy
Why is facilitated diffusion saturable, whereas channels are not?
Facilitated diffusion requires a receptor protein to CARRY the molecule across the membrane = ‘shepard taking sheep across a fence’
Ion channel is either open or closed; if open, ions move through; non saturable = “opening the gate”
What are the differences between facilitated diffusion and active transport?
Facilitated diffusion
- Requires protein carrier in the membrane
- Saturable
- Substances are transported down their concentration gradient
- No energy required
Active transport
- Substances are transported up their concentration gradient from an area of lower concentration to an area of higher concentration
- Requires Energy
How can you tell if a substance is moved by active transport?
Substance will be accumulated on one side of the membrane
How can cells have 35 fold higher concentrations of K+ inside than in the surrounding blood?
Through active transport
How do cells remove sodium?
Requires the sodium potassium pump (active transport)
Uses an integral membrane protein
PROCESS…
- 3 Na+ enter the pump (protein) on the inside of the cell
- Binds an ATP to the protein; pump is kinased (using phosphate from ATP)
- Protein will change shape and release Na+ to the outside of the cell
- Two K+ will enter the pump on the outside of the cell
- Phosphate is removed
- Protein changes shape and releases K+ to inside of the cell
Why does the toxin from poison arrow frogs kill you slowly and painfully?
Oubain block dephosphorylation (remove phosphate)
Cannot remove phosphate from ATP
Cannot pump ions; cells will swell and burst
Why are cardiac glycosides useful for treating heart patients?
Cardiac glycosides have similar effects as oubuain
Ex: digitoxigenin
Cause a slight build up of Na+ in the heart muscle cells by slightly interfering with dephosphorylation of ATP
*heart cells will swell, stimulate heart contraction
What is the similarities and difference between active transport and coupled channels?
Both require energy
Active transport will use ATP as the energy source
ATP is NOT the source of energy in coupled channels
Coupled channels will use the energy of substances moving down their concentration gradient to move another substance UP its concentration gradient
Why are coupled channels often called “secondary active transport?”
Before you can use a coupled channel, the Na/K pump has to pump the Na+ out of cell
Cells use active transport to move Na+ against its concentration gradient and accumulate it outside the cell
Then couple channels use the movement of Na+ down its concentration gradient to “POWER” the movement of something else against its concentration gradient
What is the difference between symport and antiport?
Symport: both substances are moving in the same direction
Ex. Na+ moving down its concentration gradient releases enough energy to transport sugar against its concentration gradient
- Both are moving into cell
Antiport:
Use energy from a substance moving down its concentration gradient to another substance up its concentration gradient
‘Revolving Door’
- Substances will bind to opposite integral proteins and are exchanged
Why do cells lining the small intestine have two different kinds of glucose transport proteins?
Intestines use symport if glucose and sodium…
Cells use concentration of Na+ to import glucose against its concentration gradient
What are ionophores, and why are they so deadly?
Ionophores are antibiotics that transport ions across a membrane
*Picture
Ionophores dissipate concentration gradients so concentration gradient cannot be built without a concentration gradient, you can’t have coupled channels
What is metabolism, and what is the difference between anabolism and catabolism?
Chemical reactions that occur in cells
Anabolism: reactions that build molecules
Catabolism: reaction that break down molecules (hydrolysis)
Why do cells need energy, and what is the difference between potential energy and kinetic energy?
Cells need energy to do “work” - maintain processes associated with life
Potential energy: stored energy
(living organisms store energy in their chemical bonds)
Kinetic energy: energy of motion
What are the first and second laws of thermodynamics?
1: energy cannot be created or destroyed; energy can be converted from one form to another
#2: entropy (disorder) of the universe is increasing
“S” = entropy
Ex: your bedroom being messy
What is free energy?
Energy needed to break and form chemical bonds
“G” = free energy
Have to consider…
Increases enthalpy (H) which is energy in chemical bonds
AND
2 disordering influences: temperature and entropy
Free energy = ordering influences - disordering influences
Chemical reactions usually result in a change in free energy
Δ = change in
ΔG = ΔH - TΔS
Change in free energy = change in enthalpy - temperature x change in entropy
*eq used to determine if reaction is spontaneous or not (not need energy or do)
How can you predict in which direction a reaction will proceed?
What is photosynthesis?
- equation
- free energy
Using ΔG
(change in free energy)
-ΔG = exergonic reaction; products have less energy than reactants; energy released
+ΔG = endergonic reaction; products have more energy than reactants; energy absorbed by the reaction (put energy into this reaction)
CO2 + H2O → sugar + O2
(highly endergonic-photosynthesis)
→ = sun (energy)
+ΔG
How did you measure how well lactase worked in the enzyme lab?
Lactase was the enzyme that worked on the substrate ONPG
If working, then ONPG was broken down, the solution turned yellow, the absorption (measured with the spectrophotometer) increased
What is an exergonic reaction and how does it differ from an exothermic reaction?
Exergonic: reaction that releases energy; products have less free energy or more disorder than reactants
Ex: firecracker going off
Exothermic: reaction that releases heat; spontaneous if ΔS > ΔT
Why did the ONPG change color in the enzyme lab?
ONPG changed color when the enzyme, lactase, broke it down
Why can one lactase enzyme create thousands of products?
Enzymes can be used over and over
Why did the activity of the lactase enzyme vary as you changed the pH?
5.5, 7.5, 9.5
Lactase worked best at 7.5
At 5.5 environment was too acidic, enzyme denatured- no longer functional
At 9.5 environment was too basic, enzyme denatured- no longer functional
Why can’t thermodynamics tell you how fast a reaction will go?
ΔG only tells you if the reaction is exergonic or endergonic
Need to know the activation energy to determine the speed of a reaction; first need to break existing bonds; reactions with high activation energy proceed slowly
What is activation energy?
What happens If its lowered?
The minimum amount of energy needed to start a reaction
Need activation energy to break existing bonds; if you lower activation energy, the reaction will proceed faster
What is a catalyst?
catalyst lowers activation energy by stressing (putting stress on existing) chemical bonds
Therefore it increases the rate of reaction
What is an enzyme?
Biological catalyst
Increases rate of reaction of biological reactions by lowering the activation energy
Controls metabolism
Why do cells need enzymes?
Enzymes are required to make reactions associated with life go much faster
e.g. gene disorder
How do enzymes work?
Enzyme will convert the substrate to a product
- Substrate binds to a part of the enzyme called the active site
- Enzyme changes shape and stresses existing bonds in the substrate; reduced EA; reaction occurs
- Enzyme releases product
you can use the enzyme again
What is a substrate?
the molecule on which the enzyme acts
Why can some RNA molecules catalyze reactions?
RNA molecules that act as catalysts are called ribozymes
Ribozymes can change shape and put pressure on existing bonds, reducing the energy of activation
What is an active site (in an enzyme)?
The part of the enzyme that binds the substrate
What is the difference between the “lock and key” and “induced fit” models?
Lock and key: suggest that the enzyme and substrate are exact matches
Induced fit: suggests that when substrate binds to enzyme, the enzyme CHANGES SHAPE and stress existing bonds of the substrate, thus reducing activation energy; reaction occurs quickly
Why is the induced fit model favored?
Induced fit explains how the enzyme stresses bonds of the substrate
Explains why enzyme releases product
What is the catalytic cycle of an enzyme? IE(how does an enzyme work)
Need enzyme & substrate
Substrate binds to active site of enzyme
Active site changes shape to fit substrate and then stresses existing bonds of substrate to lower activation energy
Reaction occurs
Product released
Enzyme ready to find another substrate & do another reaction
Why do we know that binding and catalysis are separate activities?
Binding of substrate and catalysis are separate activities
Some drugs prevent binding; some drugs prevent catalysi
Why can we measure an enzyme’s activity by measuring the rate at which its products accumulate?
Give a lab example
The more active an enzyme is, the more products it will produce
Lab… substrate?...ONPG enzyme?...lactase products?... ONP and galactose ??is the reaction occurring?? Solution turned yellow, and then you measured the absorbance
What factors affect how well enzymes work?
Factors that affect rate of ANY chemical reaction:
- Concentration of product (increase (as you accumulate) product→ rate decrease)
- Concentration of substrate (increase substrate→ rate increase)
- Temperature
- Presence of catalyst (enzyme)
Factors that affect protein folding:
- High temperature will disrupt hydrogen bonding and hydrophobic interactions; all enzymes have an optimum temperature
- pH alters proportion of ionized amino acids; all enzymes have an optimum pH
- Salt competes with protein for hydrogen bonds with water
- Hydrophobic solvents disrupt hydrophobic interactions
- Reducing agents break disulfide bonds
- Covalent addition of a phosphate causes an enzyme to change shape; not always a bad thing; can be used to activate enzyme
How does temperature affect enzyme activity?
As temperature increases, enzyme activity increases until optimum temperature is reached; then enzyme becomes denatured
Ex: high fever 104F (will die because enzymes/proteins will denature)
Denature = enzyme loses shape
At cooler temperatures, rate of movement of substrate and enzyme is slower, decreasing the chance that they will get together; but enzymes are not denatured at cooler temperatures
at pH to high and too low it denatures at both
What is the difference between competitive and non-competitive inhibitors?
Competitive inhibitors:
Will bind to the active site and block the substrate from binding
No reaction / Slow reaction
Noncompetitive inhibitors:
Will bind to allosteric site and the active site will change shape and substrate cant bind
No reaction / Slow reaction
How are enzymes regulated?
On enzyme: active site & allosteric site (used by inhibitors or activators)
How can we tell whether an inhibitor is competitive or non-competitive?
If we have a competitive inhibitor, can overcome inhibition by adding more substrate; substrate would outcompete inhibitor for getting to active site of the enzyme
What is the difference between an active site and an allosteric site?
Active site is where the substrate binds an enzyme
Allosteric site is where an inhibitor or an activator binds and enzyme
What is an activator?
Activators bind an enzyme at the allosteric site; keep the enzyme in an ACTIVE CONFIGURATION to increase enzyme activity
e.g. enzyme-linked receptors: when signal binds, shape of enzymes changes and response will occur (increase activity)
What is a cofactor?
Cofactor- additional chemical component that aids enzyme activity
Nonprotein
Ex: metallic trace element (Mg)
What is a coenzyme?
Coenzyme- non protein organic molecule that functions as a cofactor (organic C-H)
Usually derived from vitamins
Why do you get pellagra if you don’t get enough vitamin B3?
Lack of B3 (niacin); B3 is a cofactor involved in redox reactions; it is an active part of NAD
Symptoms: inflammation of nerves, mental disorders
Why do cells have an energy currency?
Cells energy currency- intermediates that are used to transfer energy between reactions
-Most important: ATP: adenosine triphosphate NADH: electron carrier FADH2: electron carrier NADPH: electron carrier in photosynthesis CTP, GTP (krebs cycle), UTP
What is NAD and what does it do?
NAD: nicotinamide adenine dinucleotide
NADox: (oxidized form): DOES NOT HAVE ELECTRONS
NADH: DOES HAVE ELECTRON
NADH = carries 1H+ and 2 electrons
NAD+ and NADH participate in many metabolic reactions
[Cells Move Energy By Moving Electrons]
What is ATP and why is it used in so many different reactions?
ATP: Adenosine triphosphate
ATP = ADP + P-
ATP is the main energy currency for cells
Source of fuel for cells
ATP is used to drive endergonic reactions
ATP → ADP + P + Energy
How can cells perform endergonic chemical reactions?
ATP is an energy source to drive the reaction
What is a coupled reaction?
Coupled reactions run exergonic reaction and endergonic reaction simultaneously
Break down ATP into ADP + P releases energy; this energy is used for the endergonic reaction which requires energy
The exergonic reaction must release more energy than the endergonic reaction requires
What is a biochemical pathway?
Reactions in living cells that occur in sequence; product of the one reaction is the substrate for the next reaction
What is feedback inhibition, and why is it useful?
Final product of pathway binds to the allosteric site of the FIRST enzyme in pathway and inhibits
Its reaction STOPS
How do cells recover the potential energy stored in reduced organic chemicals?
Where does the energy go?
Oxidation of reduced organic molecule
Recover potential energy by extracting electrons is this
Oxidation
Reduction
Potential energy is stored in chemical bonds, especially C-H
Remove electrons from these molecules
Electrons have energy and we move energy by moving electrons
When electrons are removed through oxidation, the electrons will be picked up molecules like NAD which will become NADH
What is electron transport (when talking about respiration)?
Electrons are carried along a series of electron carriers that increase in electronegativity
As electrons are transferred from one carrier to another, energy released is used to pump H+ and ultimately to make ATP
Oxygen has to be at the bottom for the electron transport chain
NADH gets electrons and then goes to top of chain and then NAD+ goes back to get more electrons
As electrons are dropping through the chain energy is released and used to pump H+ and later make ATP
Makes some water at the end
O2 is most electronegative (rlly rlly want e-)
What is the role of oxygen in most eukaryotic cells?
Role of oxygen is to accept electrons moving down the ETC; becomes water
Oxygen is the final electron acceptor in oxidative respiration
What is the difference between oxidative respiration and fermentation?
Oxidative respiration: requires presence of oxygen to completely oxidize sugar molecules (ripping e- off sugar for NAD or FAD to pick up)
Fermentation will only occur under anaerobic conditions meaning NO O2
Organic molecule will be the electron acceptor in fermentation
Why does transporting electrons from H to O release energy?
If electrons are transported from H to O, energy is released
B/c hydrogen electrons have the most potential energy and release energy when transferred
Oxygen valence electrons have least potential energy
Oxygen is VERY electronegative