Week 2 Lecture 3 Cell Physiology

Question 1

Plasma membrane

Answer 1

-Flexible outer surface to allow cell to move and interact
-Separates the internal and external environment
-Selective barrier- maintain internal environment
-regulates flow of material in and out the cell
-role in communication - respond to other molecules
Flexible but strong barrier
Contains the cell cytoplasm
“Fluid mosaic model “
-Moving sea of lipids, many different proteins
Movement in and out the cells
-Lipid bilayer
-Proteins

Question 2

Cytoplasm

Answer 2

-contains the cellular material between the membrane and nucleus
- 2 components
Cytosol - intercellular fluid- water, solutes,suspended particles
Organelles - characteristic shape and function
-cytoskeleton
-ribosomes
-endoplasmic reticulum
-Golgi complex
- lysosomes
-mitochondria

Question 3

Nucleus

Answer 3

Large organelle
Contains most the cells DNA
Chromosomes
-genes
-control structure and function

Question 4

Lipid bilayer

Answer 4

phospholipids -75%
-lipids with phosphorus

Cholesterol - 20% - good for holding structure together
-steroid with OH group
-weak Amphipathic
-polar= OH group
-non-polar=steroid ring and hydrocarbon tail

Glycolipids - 5%
-lipids with carbohydrate group
-polar= carbohydrate group
-non-polar= fatty acid tails
-only face extracellular fluid

Amphipathic molecules
-polar= hydrophilic
-phosphate “head”

-non-polar = hydrophobic
-2 fatty acid “tails”

Facing outwards = communicating with other molecules.

Question 5

Membrane proteins integral proteins

Answer 5

Crossing whole of lipid bilayer, can resting to something that binds to the outside of the cell and cause some response inside
Extended into or through the lipid bilayer
Embedded
Transmembrane proteins
Amphipathic
Glycoproteins- types of them, will provide some sort of communication.
Proteins with carbohydrates
Protect into extracellular fluid
Oligosaccharides
-2-60 monosaccharides
-straight or branched chains

Question 6

Membrane proteins peripheral proteins

Answer 6

Not as firmly embedded
Attached to polar heads of lipids or Intergral proteins

Question 7

Glycocalyx

Answer 7

Carbohydrates of glycoproteins and glycolipids
Suagr coating = glycocalyx
Recognition
— carbohydrate pattern differs between cells
—allows cells to recognise each other
—defence
Adhesion
—cell to cell - protection
— fluid film- transport/movement

Question 8

Functions of plasma membrane

Answer 8

Barrier - separates inside and outside of cell, contain cellular material
Control- regulates the flow of substances in and out of cell
Identification - helps cell recognise other cells and respond accordingly
Signalling - intercellular communication

Question 9

Ion channels

Answer 9

Pore in the membrane
Selective transport
Specific ion can flow to get across membrane
May not be open all the time, may be gated , voltage gated -need a certain potential for channel to open.
Or gated by some other molecule, when ion binds =gate opens

Question 10

Carriers/ transporters

Answer 10

Selective movement
Polar substance/ ion
Transport specific substances across a membrane by undergoing a change in shape

Question 11

Receptors

Answer 11

Recognises and binds specific molecules
Ligand
Recognises specific ligand and alter cells function in some way

Question 12

Enzymes

Answer 12

Specific reactions
Inside or outside of cell
Catalyses reaction inside or outside cells dependent on which way the active site is facing

Question 13

Linker

Answer 13

Anchor filaments in one cell
Anchor proteins in adjacent cells
Internal and peripheral proteins

Anchor filaments inside and outside the plasma membrane, providing structural stability and shape for the cell. May Also participate in movement of the cell or link 2 cells together

Question 14

Cell identify markers

Answer 14

Tissue formation
Defence
Distinguishes your cells from anyone else’s

Question 15

Membrane transport gradients

Answer 15

Cell membranes have selective permeability
Concentration gradients
—difference in concentration in the inside vs outside of a cell

Electrical gradient
—difference in distribution or positive and negative ions
—inner surface more negatively charge, outer surface more positive
—membrane potential

Electrochemical gradient

Question 16

Passive processes

Answer 16

Move down the concentration or electrical gradient
Uses its own kinetic energy
Simple diffusion
High to low concentration

Question 17

Active processes

Answer 17

Moves against the concentration or electrical gradient
Uses cellular energy eg ATP
Eg endocytosis or exocytsosis

Question 18

Factors affecting rate of diffusion

Answer 18

Steepness of concentration gradient
Temperature
Mass of substance
Surface area
Diffusion distance

Question 19

Simple diffusion

Answer 19

Passive process
Substances move freely through the plasma membrane
Non- polar, hydrophobic molecules eg oxygen, carbon dioxide, fatty acids, steroids, fat soluble vitamins (A,D,E,K)
Small uncharged polar molecules eg water, urea

Question 20

Facilitated diffusion

Answer 20

Substances that are too polar or highly charged
Intergral proteins- channel or carrier

Question 21

Channel mediated facilitated diffusion

Answer 21

Most membrane channels are ion channels
Hydrophilic ions
Numerous - potassium and chloride ions
Fewer -sodium and calcium ions
Slower than free diffusion as limited by number of channels
Gated - change shape to allow ion into flow
—random
—regulate by chemicals/ electrical charge

Either membrane potential or other molecules

Question 22

Carrier mediated facilitated diffusion

Answer 22

Solute binds on one side
Carrier undergoes change in shape
Solute is relased on the other side
Equilibrium
Limited by number of carriers
Eg glucose, galactose, fructose

Question 23

Osmosis

Answer 23

Passive process
Water movement
—from area of high to area of low water concentration
—from area of low to area of high solute concentration
Simple diffusion- between phospholipids

Controls water content of cells
Production of CSF, aqueous humor,tears, sweat and salvia
Dysfunction related to cataracts, salivary gland dysfunction, neurodegenerative disease

Only occurs when membrane is permeable to water but not certain solutes
Equilibrium is reached
—hydrostatic pressure forces water back

Osmotic pressure
—higher solute concentration, higher the pressure
Prevents water movement

Question 24

Aquaporins

Answer 24

Aquaporins -water channels
—bi-directional
—osmotic gradient

Question 25

Osmosis- cell shape and volume

Answer 25

Cytosol osmotic pressure = interstitial osmotic pressure

Cell volume remains constant

Cell shape and volume changes if placed in solutions with different osmotic pressure

Tonicity of solution - change volume of cell by changing water content

Isotonic - concentration is the same

Question 26

Hypotonic solution

Answer 26

Lower concentration of solute than cytosol
Water entres cells after than it leaves
cells swell and rupture - lysis

Question 27

Hypertonic solution

Answer 27

Higher concentration of solute than cytosol
Water leaves cells faster than it enters
Cells shrink - crenation

Question 28

Clinical uses of solutions

Answer 28

• I.V. Isotonic solutions eg isotonic saline

Hypertonic solutions eg cerebral oedoma
—removes water from interstitial fluid into blood
— kidneys excrete excess water

Hypotonic solutions eg dehydration
—water moves from blood to interstitial fluid to cells