1
Q
plasma membrane
A
Plasma membrane is said to be a fluid mosaic model
- Means its always in a state if change, not a static structure
- It can respond to environment around It
2
Q
Structure and function of membrane
A
- Boundary of cells – encloses and supports contents
- Separates intracellular vs. extracellular materials/ environment
- Controls what moles come into and out of the cell
- Base structure is a phospholipid bilayer with the phosphate group on the outside because they are hydrophilic, meaning they like water and the lipid tails on the inside of the membrane are hydrophobic, don’t like water
- So water liking on both sides with the phosphate and water disliking in the middle with the phospholipids
- There also a number of proteins that are present in the membrane e.g. glycoprotein
- There are membrane channels which are just protein channels that allow things to move from one side to the other very easily
- Integral membrane proteins- membrane proteins that are inserted into the membrane
- Browny yellowy strands – these are part of the inferior cytoskeleton of the cell which tends to give the cell shape and also helps organelles themselves- so the cytoskeleton is actually attached to the plasma membrane so the hole cell is in really close connection with messages going back and forward all the time
3
Q
Plasma membrane — fluid mosaic model
A
- Attaches cells to other cells and to the surrounding matrix- cell to cell adhesion
- Cells communicate with their environment through their cell membrane
- Determines what can move into and out of the cell (selectively permeable)
Intra and extracellular environment is different - Difference in charge across membrane- membrane potential
- Structure is a fluid mosaic model
- Lipid bilayer
Phospholipids
Cholesterol - Proteins
Inserted in the lipid bilayer
Peripheral or integral
Many are involved in transporting molecules across the cell membrane, e.g. channel proteins, carrier proteins, ATP powered pumps
4
Q
Transport proteins – channel proteins
A
- A channel protein forms a tiny channel through the plasma membrane so that molecules of a certain size, shape and charge can pass through
- There’s non-gated ion channels
Always open - Gated ion channels
Opened or closed by certain stimuli
5
Q
Transport protein – Carrier protein
A
- Also called transporters
- Integral proteins move ions from one side of the membrane to the other
Specific binding sites
Protein changes shape to transport ions or molecules
Resumes original shape after transport
Uniporters (carries 1 molecule), symptorters (carries 2 molecules in the same direction across the membrane), antiporters (carries 2 molecules in opposite directions across the membrane)
6
Q
ATP-powered transport
A
- Requires energy in form of ATP
- Transports substances against their concentration gradient, so the cell can accumulate substances
- E.g. sodium potassium pump
- Sometimes you need more glucose even though it’s got a lot, e.g. glucose, to do so you need to do it with energy
7
Q
Diffusion and osmosis – first principles
A
All molecules are in a state of random motion (kinetic energy)
Solute
Dissolved substances in a solution
e.g. glucose, sucrose, ions (Na+, K+, Cl-)
Solvent
Liquid that holds solutes
Generally water
Solution
Mixture form when solute is dissolved in solvent
8
Q
Diffusion
A
- When molecules move from an area of high concentration to an area of lower concentration
- Continues until molecules have evenly distributed themselves throughout the solution
9
Q
Diffusion through cell membrane
A
- Firstly there are certain specific non-lipid soluble molecules or ions diffuse through membrane channels
- Other non-lipid soluble molecules, for which membrane channels are not present, cant enter the cell
- Lipid soluble molecules diffuse directly through the plasma membrane
10
Q
Facilitated diffusion
A
- Is a specialised form of diffusion that’s important for large water soluble molecules or molecules with an electrical charge
- Larger proteins that cant just move through a simple membrane so they have to have a specific transport mechanism
- Amino acids and glucose in, manufactured proteins out
- Passive- no energy, large molecules move down concentration gradient, from high concentration to low concentration
11
Q
osmosis
A
Is the diffusion of water across a selectively permeable membrane, e.g. the plasma membrane
A selectively permeable membrane lets water to pass through but any solutes dissolved in the water
If the beaker contains distilled water (water with no solutes), water molecules will move back and forth across the membrane at the same rate and the water level stays the same on both sides
12
Q
Effect of concentration of the solution
A
- we can see that the concentration of the solute determines how much water moves across the membrane
- So the more concentrated a solution is, the more that solution will ‘pull’ water towards it
- A dilute or weak solution with a small number of solutes will only have a weak ‘pull’ on water
- A concentrated solution with a large number of solutes will have a strong ‘pull’ on water
13
Q
osmolarity
A
- This ‘pull’ on water created by soliutes is termed the solution’s osmotic pressure or osmolarity
Measured in Osmoles/L or mOsmoles/L (milliolsmoles) - Generally in the body we are working with solutions which are fairly dilute so we can use the unit mOsmoles/L
- As we can see the osmolarity of a solution is directly related to the concentration of the solution – the more ions there are in the solutions the more pull it will have on water, hence higher osmolarity
- A weak solution will have a low osmolarity value
- A more concentrated solution will have a higher osmolarity value
- A solution that has an osmolarity of 100mOsmol/L will have a smaller ‘pull’ on water that a solution which has an osmolarity of 300mOsmol/L
14
Q
Osmolarity and body cells
A
- Body fluids have many dissolved solutes
- Body fluids can be divided into
Intracellular
Extracellular (intercellular and intravascular- inside blood vessels) - The osmolarity of the intracellular fluid of a normal cell under normal conditions is approximately 290mOsmol/L
15
Q
Isotonic solution
A
- When a cell is placed in a solution that has the same osmolarity as the inside of the cell, the solution is called isotonic
- Water will move between the intracellular and extracellular fluid at equal rates (no net movement of water) and the cell is happy
16
Q
Hypertonic solution
A
- If we place a cell in a solution that has a higher osmolarity than the inside of the cell, its said to be hypertonic
- The solution with the higher osmolarity contains greater concentration of the solutes
- Cells ends up shrinking
- The solution is hypertonic
So it exerts a stronger ‘pull’ on water
Water is literally pulled out of the cell
The cell loses water and shrinks
17
Q
Hypotonic solution
A
- Has a lower osmolarity than inside the cell which means it contains a lower concentration of solutes, so solution is said to be hypotonic
- So placing a cell in a solution that has a lower osmolarity than the inside of the cell, hypotonic
- Cell gets bigger
- The solution is hypotonic
In this case the cell exerts a stronger ‘pull’ on water
Water is literally pulled into the cell
The cell takes in water – swell – burst!
18
Q
Osmosis and body cells
A
Understanding these principles is important when explaining conditions which move water from one body compartment to another
- So if we had a patient who’s dehydrated
- Then they need to be infused with a solution via intravenous drip (IV drip) to treat extreme dehydration. Need to rehydrate and encourage fluid movement back into cells. What solution could you use?
Isotonic (slightly dehydrated)– will replace extracellular fluid, e.g. 290 mM solution
Hypotonic (severely dehydrated)– will help replace intracellular fluid e.g. 5% dextrose in water (when you first give it, then the dextrose is metabolised and there is ‘free water’ to move into cells. Give slowly and only to some patients)
- If you have Edema (bad excess fluid accumulating in their cells and tissues). Giving a hypertonic solution will encoiurage fluid to move out of the cells and tissues and into vascular system to be removed by the kidneys
Administer slowly and with caution
Not to be given to patients with kidney or heart disease
19
Q
Metabolism
A
- Total of all chemical processes that occur in the body
- Metabolism includes
Catabolism - Energy-releasing process
- When large molecules are broken down to smaller molecules
Anabolism - Energy-requiring process
- Where small molecules joined to form larger molecules
Anabolism - Is when 2 or more reactants chemically combine to form a new and larger product
Chemical bonds made, energy stored in bonds
Responsible for growth, maintenance and repair
Produce chemicals characteristic of life; carbohydrates, proteins, lipids and nucleic acids
Catabolism - A large reactant is broken down to form smaller products
Chemical bonds broken, energy release
Energy in carbohydrates, lipids, proteins is used to produce energy which drives anabolic reactions, e.g. active cell membrane transport, muscle contraction, protein synthesis
20
Q
Energy
A
- The capacity to do work
Potential energy - Stored energy that could do work but isn’t
Kinetic energy - Energy that is actually doing work and moving matter
Conservation of energy mass - Energy can be converted from one type to another but not created or destroyed
Our focus is chemical energy (and heat energy)
21
Q
Chemical energy and ATP
A
- Energy is stored in chemical bonds
- Breaking chemical bonds releases energy
- This energy can then do work
- There is a large amount of energy stored in the chemical bonds of nutrients
- When nutrients (e.g. glucose) are broken down energy is released
- This energy is used to combine adenosine diphosphate ADP with an inorganic phosphate molecule (Pi) to make ATP
- ATP stores the energy released from breaking the chemical bonds
- ADP + Pi -> ATP
- Some energy released from breaking a chemical bond is not captured and stored as ATP but is lost as heat
- Heat is used to maintain body temperature
22
Q
ATP and potential energy
A
- ATP is the cells preferred way to store energy
- The small amount of energy stored in each molecules of ATP is easier for the cell to access that the larger amount stored in nutrient molecules
- When the cell needs energy it breaks down ATP to ADP
- ATP -> ADP + Pi + energy
- This energy can be used by the cell to make new proteins, repair a damaged cell membrane, drive active transport across a membrane
- So the 2 equations we are interested in
- ADP + Pi + energy -> ATP
- ATP -> ADP + Pi + energy
23
Q
Cellular respiration
A
- Process that breaks chemical bonds in food to produce energy which is stored as ATP Three main stages 1. Glycolysis Cytoplasm 2. Citric acid cycle Mitochondrial matrix 3. Electron transport chain/ oxidation phosphorylation Inner mitochondrial membrane
24
Q
Glycolysis
A
- First stage of cellular respiration
- Occurs in cytoplasm
- Breaks down 1 glucose molecules (6 carbon sugar) into 2 pyruvate molecules (3 molecules)
- Uses 2 ATPs in early stages
- Produces 4 ATP = net production of 2 ATP
- Produces 2 NADH molecules
These are used in oxidative phosphorylation to produce more ATP - Is anaerobic – does not require oxygen
- If oxygen is available pyruvate moves into the 2nd stage – the citric acid cycle
- If oxygen is not available, pyruvate gets converted to lactic acid
- at the end of glycosys = 1 glucose 2 pyruvates + 2 ATP + 2 NADH
- Whats left over can be transferred to next stage
25
Citric acid cycle
- Stage 2
- Occurs in matrix of mitochondria
- Acetyl coenzyme A formation
- Before the citric acid cycle begins:
Pyruvate (3C) is converted to acetyl CoA (2C) producing 1 NADH and 1 CO2
Each glucose we started with produces 2 pyruvates
For each glucose molecule, we have: 2 Acetyl CoA + 2 NADH + 2 CO2
- Acetyl enters the citric acid cycle and is transferred to a 4 C molecule to make a 6 carbon molecule citrate
- The citrate then goes through a series of chemical reaction and loses two C groups as 2 CO2 end up back as 4 C molecules ready to go through another cycle
- Every turn of the cycle produces 1 ATP + 3 NADH + 1 FADH2 + 4CO2
- The cycle turns twice for every glucose that enters glycolysis
- 1 glucose 2 pyruvate 2 acetyl CoA 2 ATP + 6 ATP 2 FADH + CO2
26
What are NADH and FADH2
Stage 3 involved
- Molecules that carry electrons
- These molecules collect electrons that are produced when chemical reactions occur during glycolysis and the citric acid cycle
- E.g NAD+ + 2e- + 2H+ NADH + H+
- They transport these electrons to the electron transport chain in the inner mitochondrial membrane, donate the electrons to the membrane carriers, and oxidative phosphorylation occurs to generate ATP
- NADH and FADH2 make ATP in the electron transport chain
27
oxidative phosphorylation
32-34 ATP, most energy produced by this
HSF
flashcards
Decks in class (8)
# Cards
