2.1.5 Biological membranes Flashcards
What are the roles of membranes within cells?
- compartmentalisation between organelles and cytoplasm;
lysosome = hydrolytic enzymes need to be kept separate from other organelles;
controls what enters and leaves the organelle - allows for conc gradients to be established and maintained;
- embedding of enzymes into the membrane
What are the roles of membranes at the surface of cells?
- act as partially permeable barriers and control what enters and leaves the cell e.g water, ions, gases
- site of chemical reactions
- cell signalling
What is cell signalling?
communication between cells;
cell recognition;
cells working together;
to trigger a response inside the cell;
Why do phospholipids arrange themselves in a bilayer at the cell surface?
the hydrophilic heads orientate themselves towards water and the hydrophobic tails orientate themselves away from water;
there is water outside the cell; (extracellular fluid)
and there is water inside the cell (cytoplasm)
Why is the membrane called ‘fluid’?
- components in membrane move around + flexible
Why is the membrane called ‘mosaic’?
- lots of proteins embedded
What is the function of glycoprotein and glycolipids?
cell recognition;
cell signalling;
act as antigens;
act as antigens;
cell adhesion;
What do channel proteins transport?
large and polar substances
What do carrier proteins transport?
polar substances
What is the role of cholesterol?
- found between the tails of the phospholipids
- regulates fluidity
- more cholesterol = less fluid the membrane is
What 3 factors affect the permeability of cell membranes?
1) heat
2) ethanol
3) detergents
How does heat effect the permeability of cell membranes?
as temp increases, the phospholipids gain kinetic energy;
this causes gaps to appear between the phospholipids;
the membrane becomes more permeable;
at high temp the proteins denature
What occurs to cell membrane when put in cold temperature/freezing?
when water freezes it expands;
forms ice crystals which pierce and damage the cell membrane;
How does ethanol effect the membranes permeability?
ethanol dissolves the phospholipid bilayer;
high conc of ethanol make the membrane more permeable;
same with detergent
PAG; What should be controlled in the beetroot expt?
length of beetroot;
same species;
same volume of water;
PAG; Why do you dry beetroot samples when you have cut them?
to remove any excess pigment caused by damaging the membranes in the cutting process
What is diffusion?
the net movement of molecules from an area of high concentration to an area of low concentration
What is facilitated diffusion?
diffusion via proteins
channel: ions
carrier: large (glucose, amino acids)
What is active transport?
movement of molecules against the concentration gradient (low to high);
use of carrier proteins;
ATP required;
Describe the process of exocytosis?
cytoskeleton contracts;
to move the vesicle to the cell plasma membrane;
the membrane and the vesicle fuse;
releasing it’s contents
endocytosis the opposite
= both require ATP
What is osmosis?
the net movement of water molecules;
from a region of higher water potential to an area of lower water potential;
through a partially permeable membrane;
What is meant by hypotonic?
water moves inside of a cell as the external solution has a higher water potential
What is meant by hypertonic?
water moves out of the cell as the external solution has a lower water potential
What happens if red onion cells are placed in a hypotonic solution?
water moves in down the water potential gradient;
by osmosis;
water enters the vacuole;
vacuole pushes out and puts turgid pressure on the cell wall;
cells become turgid
