Topic 2 Flashcards
Features that increase the rate of gas exchange
- Lots of alveoli = large surface area for diffusion to occur across
- alveolar epithelium and capillary endothelium are each only one cell thick = short diffusion pathway
- all alveoli have good blood supply from capillaries —> they constantly take away oxygen and bring carbon dioxide maintaining the concentration gradient
- breathing in and out refreshes the air in the alveoli keeping the concentration gradient
Properties of gas exchange surfaces
- the surfaces have a high volume to surface area ration e.g. alveoli
- they surfaces are thin so there is a short diffusion pathway
- the organism also maintains a steep concentration gradient of gases across the exchange surface
Ficks Law
Rate of diffusion = (area of diffusion surface x difference in concentration) / thickness of diffusion surface
Fick’s law calculates rate of diffusion
Phospholipid molecules in the membrane
- head contains phosphate group it is hydrophilic (attracts water)
- tail is made of two fatty acids it is hydrophobic (repels water)
- because of this the molecules automatically around themselves into a bilayer
- with the tails face inwards making the inside hydrophobic
- and the heads facing outward on either side of the membrane
- this means the membrane doesn’t allow water soluble substances like ions through it
Fluid Mosaic other molecules in the phospholipid bilayer
-protein molecules are scattered through the bilayer
(Like tiles in a mosaic)
- because the phospholipid bilayer is fluid, the proteins can move around within in it
- proteins that have a polysaccharide attached are called glycoproteins
- some lipids also have a polysaccharide chain attached to them these are called glycolipids
- cholesterol is also present in the membrane it’s fits in between the lipids forming bonds with them —> this makes the membrane more fluid
- channel proteins allow larger molecules and ions to pass through the membrane
Osmosis
Osmosis is the diffusion of free water molecules across a partially permeable membrane from an area of higher concentration of water molecules to an area of lower concentration of water molecules
Facilitated diffusion: carrier and channel proteins
Carrier proteins:
- move large molecules into and out of the cell down their concentration gradient
- different carrier proteins facilitate the diffusion of different different molecules
1/ a larger molecule attaches to a carrier protein
2/ the protein changes shape
3/ realises the molecule on the other side of the the membrane
Channel proteins:
- form pores in the membrane for charged particles to diffuse through (down their concentration gradient)
- different channel proteins facilitate the diffusion of different charged particles
Active Transport
- a molecule attaches itself to the carrier protein
- the protein changes shape
- the molecule is released on the other side
- difference between Active transport and facilitated diffusion using carrier proteins: energy is used in Active transport
—> this energy comes from ATP - ATP is produced by respiration
- it’s an immediate source of energy
- when ATP is hydrolysed the energy is released
- this allows the molecule to move against its concentration gradient
Endocytosis
- some molecules are too large for carrier proteins
- instead the cell surrounds a substance with a section of its cell membrane
- the membrane forms a vesicle inside the cell containing the ingested substance
- also uses ATP for energy
Exocytosis
- substances produced by the cell need to be released by the cell e.g. digestive enzymes and lipids need to be released from the cell
- vesicles containing these pinch off from the sacs in the Golgi apparatus and move towards the cell membrane
- the vesicles fuse with the cell membrane and release their contents outside of the cell
- membrane proteins are inserted straight into the cell membrane
- exocytosis uses ATP as an energy source
Globular Proteins
- round compact proteins made up of multiple polypeptide chains
- chains are coiled up so that the hydrophilic parts are on the outside and the hydrophobic parts are on the inside
- this makes them soluble —> easily transported in fluids
- e.g. Haemoglobin
Fibrous Proteins
- long, insoluble polypeptide chains —> tightly coiled around each other to form a rope shape
- the chains are held together by lots of bonds e.g. disulphide and hydrogen bonds which make the proteins strong
- because they are strong they are found in supportive tissue
- e.g. collagen
Primary Structure (inc. bonds)
- The sequence of amino acids in the polypeptide chain
- amino acids are linked together by condensation reactions
- peptide bonds hold together the amino acids and therefore the primary structure
- the amino aid sequence determines what bind will from and how the protein will fold up into its 3D structure
- determines 3D structure and properties
Secondary Structure (inc. bonds)
- polypeptide chain does not remain straight and flat
- hydrogen bonds form between the amino acids in the chain
- making it automatically coil up into an alpha helix or a beta pleated sheet
Tertiary Structure (inc. bonds)
- the coiled or folded chain of amino acids is often folded further
- more bonds form between the different parts of the polypeptide chain:
- ionic bonds: attractions between negative and positive charges on different parts of the molecule
- Disulfide bonds: whenever two molecules of the amino acid cysteine come into close contact the sulphur Atom in one cysteine bonds to the the sulphur in the other (forming a disulfide bond)
- Hydrophobic and Hydrophilic interactions:
Hydrophobic groups automatically clump together this makes the hydrophilic groups get pushed to the outside this affects how the protein folds up into its final structure - hydrogen bonds
- the tertiary structure forms the final structure of proteins made from a single polypeptide chain
Structure of amino acids
R group
Amine or amino group -NH2
Carboxyl group -COOH2
Fluid mosaic model is partially permeable this means…
… small molecules can move through the gaps in between the phospholipids but larger molecules but use methods of facilitated diffusion
What do enzymes do
- catalyse metabolic reactions
e. g. cellular = respiration and organism = digestion
intracellular and extracellular
- intracellular = enzyme catalyses reactions inside the cell
- extracellular = enzyme catalyses reactions outside of the cell
what is an enzyme
- protein
- that catalyse chemical reactions by working as biological catalysts
structure of enzymes
- active site: specific shape, where the substrate binds
- highly specific due to their 3D structure, only catalyse specific reactions
How do enzymes speed up reactions?
- enzymes lower the energy required for a reaction to start (activation energy) of reactions
- this speeds up the rate of reaction
- they reduce the repulsion between molecules that need to be bonded - bond more easily
- active site puts a strain on molecules that need to be broken down - break down more easily
Lock and Key Model
- enzyme is the lock
- substrate is the key
- active site of enzyme is specific to a particular substrate the same way a lock has a specific key
Induced Fit Model
- explains why enzymes are so specific and only bind to certain substrates
- must be the right shape AND be able to make the active site change shape the right way
Tertiary structure of enzyme
- specific, usually only catalyse one reaction
- this is because only one complementary substrate will fit the active site
- active site shape is determined by tertiary structure which is determined by the primary structure of an enzyme
- tertiary structure altered = substrate doesn’t match active site = not enzyme-substrate complete and no catalyzed reaction
- tertiary structure may be altered by pH or temperature or mutation in primary structure
enzyme concentration affects the rate of reaction
- the more enzyme, the more active sites and the more likely a collision between the substrate and enzyme is
- therefore more likely to form enzyme-substrate complex and the rate of reaction is increased
- but if amount of substrate is limited there may become a point where there is more enzyme than substrate
- in this case adding enzymes has no further effect on the rate of reaction
