Chapter 4- Cell Membrane Flashcards
describe the structure of phospholipids
Their heads face the water as they are polar while their tails face out of the water as they are non-polar
describe the structure of a cell membrane/ features of the fluid mosaic model
- they are a bilayer of phospholipids
- They have proteins that are either polar or non-polar
- the phospholipid tails point inwards which forms a hydrophobic interior while head faces outwards
- proteins are found in the inner layer, outer layer or span along the whole membrane
- Most float and some are fixed
- many proteins are either glycoproteins or glycolipids
- molecules of cholesterol are found as well
- some phospholipid tails are saturated and unsaturated. The more saturated they are the longer the tails, hence, the less fluid the membrane is
why are cell membranes described as a fluid mosaic model
Fluid: both the phospholipids and proteins can move about and have a fluidity nature. phospholipids can move sideways while proteins can move within.
Mosaic: This is due to the scattered arrangement of proteins within the bilayer
what is the role of phospholipids in the cell membrane
these contain a lipid bilayer and can control what substances enter and what cannot leave based on their polarity
They can also act as signalling molecules
what are the roles of cholesterols in the cell membrane
-Maintains mechanical stability by getting in between the phospholipids to reduce fluidity
-can prevent polar molecules from passing through
-maintaining the correct fluidity at different temperature
>Cold temperatures: Avoid the phospholipids from packing close together
>High temps: decreasing the fluidity
what are glycoproteins and glycolipids
proteins or lipids are attached to a short carbohydrate chain which project like antenna into the water and can create hydrogen bonds to stabilise the membrane structure
What are the roles of glycoproteins and glycolipids and proteins in the cell membrane
1-Can act as receptor molecules
2-Cell to cell recognition
3-Transport proteins
4-Enzymes
5-Cytoskeleton
what do glycoproteins/lipids act as when it comes to cell recognition
They act as cell markers and are cell surface antigens. All cells have their own type of antigen
what are the 2 types of transport proteins, and what do they have that allows polar molecules to pass through
They have hydrophilic channels for polar molecules.
carrier and channel proteins
what is cell signalling
A molecular mechanism by which cells detect and respond to external stimuli including communication between cells
outline the 3 main steps taken in cell signalling
1) there’s the secretion of chemicals called ligands
2)these are transported to the target cells
3)These ligands bind to the cell surface receptors
how do receptors attach to the ligand
They are specific to the ligand
What is a transduction
The conversion of the original signal from one method of transmission to another
outline the typical signalling pathway
-the signal arrives at a protein receptor in a cell surface membrane
-The receptor is able to recognise this signal.
- the signal brings about a change to the receptors shape
-cell transduction occurs whereby the receptor can interact with the next component of the pathway
How is a second messenger introduced
- This is stimulated by a G protein.
- several second messengers can be released in response to only one receptor being stimulated
- This can represent an AMPLIFICATION of the original signal
How does the second messenger operate
These activate enzymes which further activate more enzymes which bring about a required change in cell metabolism
What is the name of the sequence of events triggered by the G protein
Signalling Cascade.
What are 3 alternative ways a receptor can alter cell activity
>
- Opening an ion channel resulting into a change in membrane potential
- act directly as a membrane bound enzyme
- Acts as an intracellular receptor
what different mechanisms may occur for movement into and out of the cell
-Osmosis
-simple diffusion
-facilitated diffusion
-Bulk processes
-active transport
which molecules pass through via diffusion
-water molecules- small enough
-hydrophobic molecules
-Oxygen and carbon-dioxide
Which factors affect diffusion
-temp
-surface area
-nature of molecule
-steepness of the concentration gradient
Examples of where in the body surface area increases diffusion
-Microvilli in the ileum
-Cristae in the mitochondria
-interconnected alveoli in the lungs
relationship between diffusion and surface area to volume ratio
Proportional
Relationship between size of cell to surface area to volume ratio
-Inverse
-the larger the cell the smaller the S.A to volume ratio
What is facilitated diffusion
The diffusion of substances through a transport protein, either carrier or channel (gated). These proteins provide a hydrophilic passage allowing polar molecules/ions to pass.
Describe Channel proteins
-fixed shape
-water filled pores which select the molecules passing through
Describe Carrier proteins
-Can change shape based on which molecule is entering
How is the rate of F.D facilitated
-Depends on the number of channel and carrier proteins available and open/closed.
What is osmosis
*KEY WORDS
Net diffusion of water molecules from a region of higher water potential to a region of lower water potential through partially permeable membrane, until an equilibrium is reached.
What is water potential
a measure of the tendency of water molecules to move from one place to another
What affect water potential
-Concentration of the solutes
-Pressure
water potential is measured in
Kilo pascals with the highest being 0kPa
What are the 3 solutions discussed in osmosis
-Hypertonic: concentrated
-hypotonic: dilute
-isotonic
What is Haemolysis
When animal cells are placed in dilute solutions they become turgid after absorbing water however eventually burst due to no presence of a cellulose cell wall.
What is crenation
When animal cells are placed in a hypertonic solution, they become flaccid after losing water to the environment and eventually shrink
what happens when plant cells are placed in a hypotonic solution
-this results in the cell gaining water which increases its water potential and the cell wall resists the expansion of the protoplast and the cell is said to be turgid.
what is plasmolysis
After exposed to a hypertonic solution, the water molecules leave the plant cell and pressure goes down. the water molecule move down their water potential gradient. This results into the protoplast gradually shrinking and pulling away from the cell wall.
What is active transportation in cell membranes
This is the movement of molecules or ions through TRANSPORT PROTEINS across a cell membrane AGAINST their concentration gradient using energy from ATP
What is another name for carrier proteins in A.T
Protein PUMPS
How do carrier proteins use energy
-This energy is used to change the shape in order to allow molecules to move across the membrane
What is co-transport
-this process involves 2 molecules being transported across the cell membrane at the same time which the movement of each is dependant on each other
what is a strength of co-transport
Uses less energy.
Bulk transport requires energy, TRUE/FALSE
TRUE
What is endocytosis
This is the bulk movement of lipids or solids INTO the cell by the infolding of the cell surface membrane to form vesicles containing the substance it requires.
what are the 2 forms of endocytosis
1)phagocytosis- bulk transport of SOLIDS
2)Pinocytosis- bulk transport of LIQUIDS
What is exocytosis
This is the bulk movement of molecules OUT of the cell by FUSION of the vesicles containing the substance to be removed from the cell. It requires ATP
examples of substances secreted by exocytosis
-Digestive enzymes
-Materials to build cell walls
-hormones
both endo- and exocytosis are affected by the _____ nature of the cell membrane
FLUID
