1 nucleus the nucleus is the controller of the cell. it is surrounded by the nuclear envelope which...

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NucleusNucleus

• The nucleus is the controller of the cell.

• It is surrounded by the nuclear envelope which controls what substances may exit/enter the nucleus.

• It contains DNA and the nucleolus.

• DNA is termed the “genetic blueprint” and directs all protein synthesis.

• The nucleolus makes ribosomes.

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Nucleus-PlantNucleus-Plant

• The nucleus is the controller of the cell.

• It is surrounded by the nuclear envelope which controls what substances may exit/enter the nucleus.

• It contains DNA and the nucleolus.

• DNA is termed the “genetic blueprint” and directs all protein synthesis.

• The nucleolus makes ribosomes.

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RibosomesRibosomes

• Ribosomes are protein factories. All protein synthesis occurs within the ribosome.

• They may be fixed (attached to the endoplasmic reticulum) or free floating in the cytoplasm

• They are composed of rRNA and proteins.

• Free floating and fixed:

Cell

Endoplasmic Reticulum

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Ribosomes-PlantRibosomes-Plant

• Ribosomes are protein factories. All protein synthesis occurs within the ribosome.

• They may be fixed (attached to the endoplasmic reticulum) or free floating in the cytoplasm

• They are composed of rRNA and proteins.

• Free floating and fixed:

Cell

Endoplasmic Reticulum

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Endoplasmic Reticulum

• The endoplasmic reticulum or ER is a network of channels which assist in the synthesis and transport of cellular products.

• There are two types:

• smooth ER which is involved in the synthesis of lipid products such as steroid hormones.

• Rough ER which has ribsosomes attached to it & is involved in protein synthesis.

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Endoplasmic Reticulum-Plant

• The endoplasmic reticulum or ER is a network of channels which assist in the synthesis and transport of cellular products.

• There are two types:

• smooth ER which is involved in the synthesis of lipid products such as steroid hormones.

• Rough ER which has ribsosomes attached to it & is involved in protein synthesis.

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Golgi ApparatusGolgi Apparatus

• This organelle consists of tubular channels which function to assemble, and check proteins coming from the rough ER.

• The golgi apparatus also ensures that the completed proteins go to the appropriate

area of the cell. (that proteins for the cell membrane get to the membrane, proteins hormones exit the cell etc.)

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Golgi Apparatus-PlantGolgi Apparatus-Plant

• This organelle consists of tubular channels which function to assemble, and check proteins coming from the rough ER.

• The golgi apparatus also ensures that the completed proteins go to the appropriate

area of the cell. (that proteins for the cell membrane get to the membrane, proteins hormones exit the cell etc.)

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Lysosomes Lysosomes

• Lysosomes contain powerful digestive enzymes which break apart anything that gets inside it.

• They are important in protection (splitting bacteria) as well as, old organelles.

• Lysosomes are able to release the end products for reuse in the cell.

• It is important that the lysosome doesn’t rupture or the enzymes would digest the cell.

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Mitochondria

• Mitochondria are the “powerhouses” of the cell.

• They are responsible for carrying out aerobic cellular respiration.

• This process forms ATP from the food we eat and requires oxygen.

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Mitochondria-PlantMitochondria-Plant

• Mitochondria are the “powerhouses” of the cell.

• They are responsible for carrying out aerobic cellular respiration.

• This process forms ATP from the food we eat and requires oxygen.

Back

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Cytoskeleton

• The cytoskeleton functions as the “muscles and bones “of the cell.

• It consists of:• Microfilaments: which help

the cell to move (muscle contraction)

• Intermediate Filaments: which prevent the cell from being pulled apart.

• Microtubules: function in maintaining the cell shape.

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Central VacuoleCentral Vacuole

• Large organelle• Consists of mostly water, plant pigments, and

toxins.• Functions for storage of nutrients and

pigments, and retains waste products.• The pigments which give a flower its color are

stored in the vacuole.

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ChloroplastsChloroplasts

• Contain green pigment termed chlorophyll.

• Function in photosynthesis

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The importance of water to living The importance of water to living organismsorganisms

Metabolic role of water:• 1. Hydrolysis• 2. Medium for chemical reactions• 3. Diffusion and osmosis• 4. Photosynthetic substrate/raw material

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Water as a solvent: It readily dissolves many substances & therefore is used for• 1. Transport• 2. Removal of wastes• 3. SecretionsWater as a lubricant:• 1. Mucus• 2. Synovial fluid• 3. Pleural fluid• 4. Pericardial fluid• 5. Perivisceral fluid

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Supporting role of water: because of its incompressiveness, support is possible• 1. Hydrostatic skeleton• 2. Turgor pressure• 3. Humours of the eye• 4. Amniotic fluid• 5. Erection of the penis• 6. Medium in which to liveMiscellaneous functions of water:• 1. Temperature control• 2. Medium for dispersal• 3. Hearing and balance

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22.1.1 Structure of the water molecule

• normal water molecule: 1H216O

• isotopes:

• heavy water - 2H216O may be harmful to living

organisms

Protoplasm , colloid, diffusion and imbibitions

1050Oxygen atom

Hydrogen atomHydrogen atom Hydrogen atomHydrogen atom0.1539 nm

0.097 nm

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ColloidsColloids

• Cytoplasm is a colloid, made up largely of protein molecules dispersed in water.

• It is hydrophillic, i.e. attracts water molecules around them and prevent them to aggregate into large particles and settle out.

• Imbibition is the process by which water is absorbed by hydrophilic colloids inside seeds at the beginning of germination.

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Water Relations of A Plant CellWater Relations of A Plant Cell

Water potential of a system is the difference in chemical potential of water in a system and that of pure water at the same temperature and pressure.

The water potential of pure water at standard temperature and pressure is “0”.

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Osmotic potential is the component of water potential that is due to the presence of solutes.

Pressure potential is the component of water potential that is due to the hydrostatic pressure.

Incipient plasmolysis is the point at which the protoplast of the cell just lost contact with the cell wall.

Plasmolysis is a condition of the cell when the protoplast shrinks away from the cell wall due to osmosis.

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Molecular MovementMolecular Movement

• Diffusion - movement of a substance from an area of higher concentration and/or pressure towards and area of lower concentration and/or pressure

• Osmosis - the diffusion of water across a semipermeable membrane

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• Click here to see the water relations movies

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PotentialsPotentials

• Osmotic Potential - the effect of dissolved solutes on water potential

• Pressure Potential - the effect of pressure on water potential

Positive pressure potential is called turgor pressure

Negative pressure potential is called tension

Water Potential = osmotic potential + pressure potential

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PlasmolysisPlasmolysis

• the shrinkage of protoplasts away from cell walls caused by loss of water by osmosis

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ImbibitionsImbibitions

• movement of water into plant tissues due to water being attracted to polar substances, e.g. cellulose and starch

• first step in germination

• can produce tremendous pressures

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Plant Enzymes

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Characteristics of Enzymes

• Most are globular proteins that act as biological catalysts

• Holoenzymes consist of an apoenzyme (protein) and a cofactor (usually an ion) or coenzyme

• Enzymes are chemically specific• Frequently named for the type of reaction they

catalyze• Enzyme names usually end in -ase• Lower activation energy

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Characteristics of EnzymesCharacteristics of Enzymes

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Mechanism of Enzyme Action

• Enzyme binds substrate(s) at active site

• Product is formed at a lower activation energy

• Product is released

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Cofactors

• provide “chemical teeth” for enzymes• sometimes referred to as coenzymes • enzymes: proteins with catalytic activity

– simple enzymes: large protein (polypeptide) that catalyzes a reaction. The enzyme gets all the “tools” (chemical teeth) it needs from the amino acids. However, there are only 20 different amino acids

– conjugated enzymes : apoenzyme + cofactor = holoenzyme

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EXAMPLE: Proteases: enzymes that cleave peptide bonds

Enzymes perform catalytic reactions such as hydrolysis; theside chains of amino acids participate in the reactions

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example of a simple enzyme

A serine protease enzyme such as chymotrypsin

Usually electron-richside chains are involvedin the catalysis

Aliphatic chains are normally involved inhydrophobic interactions

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HYDROLYTIC CATALYSIS

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Example of a conjugated enzyme

Zinc protease suchas ACE