Variety of life

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
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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. 

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Oxygen Dissociation Curves

(http://www.unm.edu/~lkravitz/Media/oxygencurve.jpg)

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Oxygen Dissociation Curves - CO2

(http://www.normalbreathing.com/images/bohr-effect5.JPG)

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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
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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
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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
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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
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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

 

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Differences between Plant and Animal Cells

(http://lusinagao.files.wordpress.com/2012/08/difference-between-plant-animal-cell-2.gif?w=540)

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