Biology topic 2B (cells)

The basic structure of all cell membranes are

the same

cell surface membranes are

partially permeable

The fluid mosaic model

phospholipid molecules form a continuous bilayer, which is fluid as phospholipids are constantly moving.

proteins are scattered through the bilayer (like tiles in a mosaic) -channel and carrier proteins.

glycoproteins

proteins with a carbohydrate attached

glycolipids

lipids that have a carbohydrate attached

cell membrane structure (diagram)

role of phospholipids

forms a barrier to dissolved (water-soluble) substances

how phopholipids form a barrier

arrange themselves- heads→ hydrophilic (outside)

tails→ hydrophobic (inside)

so centre is hydrophobic so water-soluble substances cannot dissolve through

role of cholesterol

provides stability

binds to hydrophobic tails causing them to pack tightly together and restrict movement of phospholipids.

Simple diffusion

when particles diffuse directly through the cell membrane (small molecules such as oxygen and carbon dioxide)

is diffusion active or passive

passive

limitations imposed by phospholipid bilayer

only small molecules can pass through- can pass through spaces in the phospholipids

only non-polar molecules can pass through as they are soluble so can dissolve in the hydrophobic layer.

facilitated diffusion in a carrier protein

-large molecule attaches to carrier protein

-protein changes shape to release molecule on other side

facilitated diffusion in channel proteins

forms pores in the membrane for charged particles to diffuse down

Osmosis

diffusion of water molecules across a partially permeable membrane from an area of high water potential to an area of low water potential. This is a passive process.

water potential

likelihood of water molecules to diffuse out of or into a solution

isotonic

if two solutions have the same water potential

hypotonic

solutions with a higher water potential than in the cell

hypertonic

solutions with a lower water potential than the cell

Active transport -carrier proteins

-attaches to carrier protein

-changes shape to move molecule to other side → from low to high concentration

-requires energy from ATP (undergoes a hydrolysis reaction- splitting into ADP and an inorganic phosphate which releases energy)

co- transporters are

a type of carrier protein that bind two molecules at a time.

the concentration gradient of one molecule is used to move the other molecule against its own concentration gradient.

mammalian ileum

the concentration of glucose is too low for glucose to diffuse out into the blood

so glucose is absorbed from the lumen of the ileum by co transport

antigens

molecules that generate an immune response when detected by the body

found on the surface of cells

foreign antigens

not normally found in the body

pathogens

have antigens on surface- detected by antigens as foreign

organisms that cause disease

Toxins

immune system responds to these molecules

cells from other individuals

blood transfusion- cells will have antigens that are different from ur own

triggers an immune response

antigens enable the immune system to identify

-pathogens

-cells from other organisms of the same species

-abnormal body cells

-toxins

phagocyte

a phagocyte found in the blood or tissues responds to an immune system trigger

phagocytosis of pathogens

-phagocyte recognises foreign antigens on pathogen

-cytoplasm moves round the pathogen engulfing it

-phagocytic vacuole in the cytoplasm of a phagocyte

-lysosome fuses with the phagocytic vacuole. The lysozymes break down the pathogen

-phagocyte presents the pathogens antigens on its surface → antigen presenting cell

T cells

type of white blood cell

receptor proteins on its surface bind to complementary antigens

helper T cells

release chemical signals that activate and stimulate phagocytes