Variety of life
- Biology
- Human, animal and plant physiologyBiological molecules, organic chemistry and biochemistryCellular processes and structure
- AS
- AQA
- Created by: Han2812
- Created on: 01-06-14 10:42
Haemoglobin
Haemoglobin are protein molecules, so have a quaternary structure and same pattern structure:
- PRIMARY STRUCTURE: Consists of 4 POLYPEPTIDES
- SECONDARY STRUCTURE: Each polypeptide chain is coiled into a helix
- TERTIARY STRUCTURE: Each polypeptide chain is folded into a precise shape, IMPORTANT factor - has ability to CARRY OXYGEN
- QUATERNARY STRUCTURE: All 4 polypeptide chains are linked together to form the almost spherical molecule. 4 O2 molecules can be carried as each chain has Fe2+ ion, carries O2
Role of Haemoglobin:
- Readily ASSOCIATES with oxygen at the SURFACE where gas exchange takes place
- Happens at the LUNGS --> ASSOCIATING OR LOADING
- Readily DISSOCIATES from oxygen at the TISSUES needing it
- Happens in the TISSUES --> DISSOCIATING OR UNLOADING
Different Haemoglobins
Organisms have DIFFERENT haemoglobins showing different characteristics to oxygen:
- Haemoglobins with a HIGH AFFINITY for oxygen - take up oxygen MORE EASILY but release it LESS READILY
- Haemoglobins with a LOW AFFINITY for oxygen - take up oxygen LESS EASILY but release it MORE READILY
WHY?:
- An organism living in an environment with LOW O2 requires haemoglobin that READILY combines with oxygen, if metabalism is low then doesn't matter if releases it less easily.
- An organism living in an environment with HIGH O2 requires haemoglobin that RELEASES O2 EASILY as they have a HIGH METABOLIC RATE so need more O2 in their tissues.
Different haemoglobin also have different shape molecules, as have a slightly different amino acid sequence. Depending on the shape, they either have a high or low affinity for oxygen.
Oxygen Dissociation Curves
Oxygen Dissociation Curves - CO2
Starch and Glycogen
STARCH:
- Is a POLYSACCHARIDE that is found in my plants in form of tiny grains.
- Major source of energy in most diets
- Chains of a-glucose -> GLYCOSIDIC BONDS BY CONDENSATION REACTIONS
Main role of starch is ENERGY STORAGE. Its suited for this because it's:
- INSOLUBLE - Doesn't tend to draw water into the cell by OSMOSIS
- - Doesn't diffuses easily out of cells
- Compact, so lot can be stored in small spaces
- HYDROLYSISED - forms a-glucose --> easily transported and readily used in respiration
GLYCOGEN:
- Very similar structure to starch but has SHORTER CHAINS + more HIGHLY BRANCHED
- Because made up of shorter chains - even easier to hydrolysis into a-glucose than starch
- Sometimes called 'animal' starch as major carb storage in animals in muscles + liver
- Structure suits it for storage for same reasons as starch
Cellulose
Cellulose is different from starch and glycogen because:
- Made up of B-GLUCOSE instead of a-glucose - MAJOR BUT SMALL VARIATION
- B-glucose produces fundemental differences in the structure and function of the polypeptide chains as the positions of the -H group and -OH group on a single carbon are reversed
- This means to FORM the GLYCOSIDIC BONDS, THE B-GLUCOSE MUST BE ROTATED 180 DEGREES compared to its neighbour, so some will be upside down
- This means that the -CH2OH group will be sometimes below and above the chain
- These chains are STRAIGHT, UNBRANCHED
- They run PARALLEL to one another, so HYDROGEN BONDS can form links between them
- The large number of them addeds to the strength of the cellulose, making it a very valuable structural molecule.
Cellulose is also used in plant cell walls too:
- Makes it RIGID, prevents it from BURSTING as water enters it by osmosis by exerting an INWARD PRESSURE that stops any more water coming in
- As a result, living plant cells are TURGID pushing against one another, making parts of the plant SEMI-TURGID, provides MAX SURFACE AREA FOR PHOTOSYNTHEISIS
Plant Cell Structure - Leaf Palisade Cell
MAIN FUNCTION: Carry out photosynthesis
STRUCTURE:
- LONG, THIN cell - forms a continous layer to absorb sunlight
- LOTS OF CHLOROPLASTS - arrange themselves in the best positions to collect maxiumum amount of sunlight
- LARGE VACUOLE - pushes the cytoplasm and chloroplasts to the edge of the cell
Plant Cell Structure - Chloroplasts
CHLOROPLASTS:
Chloroplasts vary in shape and size, but are typically DISC-SHAPED, 2-10um long, 1um diameter
- CHLOROPLAST ENVELOPE: Double plasma membrane that surrounds the organelle. HIGHLY SELECTIVE in what it allows to enter + leave the chloroplast
- THE GRANA: STACKS of up to 100 DISC-LIKE STRUCTURES called THYLAKOIDS. Inside these discs, is the photosynthetic pigment called CHLOROPHYLL. Some thylakoids have tubular extensions to link to others in other grana. 1ST STAGE OF PHOTOSYNTHESIS
- THE STOMA: FLUID FILLED matrix - 2ND STAGE OF PHOTOSYNTHESIS. Within the stoma, number of different structures, like STARCH GRAINS
Chloroplasts are adapted to their function of photosythesis - sunlight into energy by:
- Granal membranes provide LARGE SURFACE AREA for the chlorophyll, enzymes + electron carriers to carry out photosynthesis. These are attached to the membrane of the grana
- FLUID in the STOMA posseses all the enzymes needed to carry out 2nd stage of photosnthesi
- Chloroplasts contain both DNA and RIBOSOMES so can quickly and easily manufacture proteins needed for photosynthesis
Plant Cell Structure - Cell Wall
FEATURES:
- Consist of number of POLYSACCARIDES, such as CELLULOSE
- THIN LAYER called the MIDDLE LAMELLA, marks the boundary bewteen adjacent cell walls and cements adjacent cells together
FUNCTIONS:
- Provide MECHANICAL STRENGTH to:
- PREVENT THE CELL FROM BURSTING under the pressure created by the osmotic entry of water
- To the plant as a whole
- Allow water to pass along it and contribute to the movement of water through the plant
Differences between Plant and Animal Cells
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