Biological membranes

What do membranes cover

The surface of every cell

Functions of membranes

Partially permeable barrier between cell and environment allowing selected molecules in and out, PPM between organelles and cytoplasm allows processes to occur separately, site for biochemical reactions, site of all cell communication

Phospholipids

Type of lipid made from 2 fatty acid chain tails and a phosphate group head

What adjectives describe the head

Polar and hydrophilic

Polar

Molecules have an uneven distribution of charge

Hydrophilic

Water loving

Adjectives to describe fatty acid tails

Non polar, hydrophobic

Hydrophobic

Water hating

Why are phospholipids shape/structure what they are

Due to their polar nature and the way they interact with water

What structures do phospholipids form

Micelles, phospholipid bilayer

Micelles

Phospholipids arranged in a circle with tails pointing into the centre and heads pointing out

Bilayer

2 layers of phospholipids, tails on inside heads on outside

What kind of molecule is cholesterol

Lipid

Role of cholesterol

Controls membrane fluidity

What does more cholesterol mean

Less fluid membrane to less permeable

What makes up 45% of mass of membrane

Proteins

Type of proteins

Intrinsic and extrinsic

Intrinsic proteins

Span the width of the membrane

Functions of intrinsic proteins

Channel proteins- are carrier molecules, transport substances such as ions sugars and amino acids that can’t diffuse across the membrane

Function of extrinsic proteins

Receptors- on cytosolic side of protein(pointing out to cell) are involved in cell signalling

Glycoproteins

Are a branching carbohydrate portion of a protein that acts as a recognition size for chemicals,,hormones, enzymes or used in cell adhesion

Glycolipids

Are lipids with attached carbohydrate chain, act as a recognition site for the immune system

Cell signalling

Cells can signal each other via direct contact or messengers

Examples of messengers

Neurotransmitters, hormones

Small non polar messengers

What kind of messengers can pass through the membrane

What do messengers do that can’t pass through the membrane

Must bind to membrane bound receptors such as glycoproteins

Antagonists

Drugs that bind to normals messengers

Example of antagonists

Antiemetics- anti sickness drug

Agonists

Drugs that bind to receptors and mimic the body’s normal messengers

What is the model of cell membrane structure called

Fluid mosaic model

Absolute uncertainty

Scale on measuring device

Percentage error

Uncertainty/ volume measured x 100

Diffusion

The net movement of particles down a concentration gradient

What type of transport is diffusion

Passive

Passive transport

Only requires kinetic energy not metabolic energy (ATP)

Equilibrium

No net movement of molecules in one direction

Factors affecting the rate of diffusion

Temperature, concentration difference, surface area, thickness of membrane, size of molecules

How does temperature affect the rate of diffusion

Higher temp= higher RoD as particles have more kinetic energy and move at higher speeds

How does concentration difference affect the rate of diffusion

Large conc difference= higher RoD as overall movement will be larger

How does surface area affect the rate of diffusion

The larger the surface area of an exchange surface= higher RoD

How does thickness of membrane affect the rate of diffusion

Thinner the exchange surface = faster `RoD

How does size of molecule affect the rate of diffusion

Smaller= faster rate

Simple diffusion

Diffusion in the absence of a barrier or membrane

What do particles pass through during diffusion

Phospholipid bilayer

What needs to be true to allow for diffusion

Membrane must be permeable to particles which need to be small and non polar

Why can’t polar molecules pass through the phospholipid bilayer

The hydrophobic interior repels the positive or negative charge so ions and other polar molecules can’t pass through

Why can water pass through at a slow rate

It has slight charges so moves through but slowly

Why are membranes described as partially permeable

Some polar molecules pass through, some don’t some polar molecules pass trough easier than larger ones

How do polar and large molecules diffuse

Through the channel(intrinsic) protein

How do polar and large molecules diffuse

Through the channel(intrinsic) protein

Active transport

Movement of molecules against concentration gradient

What do cells use in active transport

Carrier proteins to pump molecules and ions across the membrane, energy

What is the energy used in active transport in the form of

ATP

ATP

Adenosine triphosphate

What produces atp

Mitochondria though respiration

When doe cells use active transport

They need more of a substance inside than outside the cell, they need a substance Whicker than simple diffusion can get it

What do cells that undertake a lot of active transport need

Lots of mitochondria

Examples of active transport

Glucose absorption from intestines, magnesium from soil, calcium in muscle cells, bulk transport (exocytosis releasing large quantities of protein from a cell)

Similarities between AT + facilitated diffusion

Through carrier proteins, both transport substances across a membrane

Differences between AT+ facilitated diffusion

AT: needs ATP, against concentration gradient, only one way

FD: doesn’t need energy, down concentration gradient, goes both ways

What does concentration refer to

The mass of solute present

Water potential

The tendency of water molecules in a system to move

What is water potential measured in

Kilopascals (kPa)

What is the symbol for water potential

Psi

What has the highest water potential

Pure water

What have lower wp than pure water

Solutions- have negative water potentials

Water potential of pure water

0 kPa

What has the higher water potential -100kPa or -40pkPa

-100

Where do water molecules move between

From a region of high water potential to a region of low/ more negative WP

Osmosis

The net movement of water molecules from an area of high water potential to a region of low water potential down a water potential gradient across a plasma membrane

Why does water move in and out of cells

The cytoplasm of a cell is a fairly concentrated solution of salts and sugars so water will either move into or out of the cell depending on the concentration of the solution in it

Why can’t plants control water potential

Due to the fluid around them

What happens to cellulose cell walls in plants when water enters via osmosis

Hydrostatic pressure increases and pushes the membrane shading the rigid cell walls

What is the pressure extend on the cell walls called

Turbot pressure

What happens when a plant cell is in a solution with a lower water potential than their own

Water is lost from the cells resulting in a reduction in volume of the cytoplasm

What does a reduction in volume of the cytoplasm lead to

The cell surface membrane is pulled away from the cell way- cell is plasmolysed

What happens when an animal cell is placed in a solution with a higher water potential that that of the cytoplasm

Water will move into the cell via osmosis and the hydrostatic pressure inside the cell will increase

Width of cell surface membrane

7nm

Why is it bad for the cell to intake more water

The cell surface membrane can’t withstand the increased pressure as it is very thin and theres

What is it called when a cell breaks/ bursts

Cytolysis

What happens when an animal cell is placed in a solution with a lower water potential than that of the cytoplasm

It will lose water causing a reduction in its volume resulting in the cell surface membrane to pucker

What is it called when the csm puckers

Crenation

What prevent cytolysis and crenation

There are control mechanisms in place that make sure that cells are surround by equal water potentials so water is not lost or absorbed by the cell