CELL PROCESSES

Part of AS91156

Transport

•Passive Transport

•Active Transport

Passive Transport

• Particles move along a concentration gradient around, into or out of the cell by the process of diffusion and without any energy expenditure by the cell.

• Examples: osmosis, plasmolysis and facilitated diffusion.

Diffusion

Spreading of a substance by the movement of particles along a concentration gradient.

Diffusion through a membrane

Cell membrane

Inside cell Outside cell

Diffusion through a membrane

Cell membrane

Inside cell Outside cell

diffusion

Diffusion through a membrane

Cell membrane

Inside cell Outside cell

EQUILIBRIUM

Osmosis

Movement of water from a high concentration [of water] to a low concentration [of water] through a semi-permeable membrane.

Plasmolysis in Plant Cells

If enough water leaves a plant cell the cell membrane shrinks away from the cell wall. The cell is said to be plasmolysed.

Plasmolysed Oxygen Weed Cells

Turgid Oxygen Weed Cells

Facilitated Diffusion

• Movement of selected types of particles across the membrane along the concentration gradient.

• Faster than diffusion.

• Movement is aided by transport proteins in the membrane.

Active Transport

• The use of energy by the cell to move particles into or out of the cell against the concentration gradient.

• Examples: exocytosis, endocytosis and ion pumping.

Exocytosis

Vesicles from golgi bodies or the endoplasmic reticulum expel their contents to the outside through the cell membrane.

Endocytosis: Pinocytosis

Absorption of liquids into vesicles formed from part of the cell membrane. (Cell drinking.)

Endocytosis: Phagocytosis

Absorption of solids into food vesicles formed from part of the cell membrane. (Cell eating.) Lysosomes then fuse with food vacuoles to digest particles.

Ion Pumping

Ion pumps are proteins that move ions across a membrane against their concentration gradient.

Sodium Potassium Nerve Cell Pump

Cell Division

MITOSIS

Cells divide to provide new cells for growth

MITOSIS

Cells divide to repair damaged tissues

MITOSIS

Cells divide to keep a large surface area to volume ratio.

The Cell Cycle

Deoxyribonucleic Acid

Deoxyribonucleic Acid

• Bases: adenine, thymine, guanine, cytosine

• Double helix• Function: genetic memory

DNA Base Pairing

DNA Base Pairing

Semi-conservative DNA Replication 1

Semi-conservative DNA Replication 2

Semi-conservative DNA Replication 3

Mitosis Photomicrographs

Interphase

Early Prophase

Late Prophase

Metaphase

Anaphase

Telophase

Cytokinesis

Centrioles

• Made from two hollow cylinders at right angles to each other.

• Forms spindle fibres to separate chromosomes in mitosis.

Enzyme Activity

Enzyme Structure

Enzymes are Globular Proteins.

Amino Acid

Three Different Amino Acids

1o Protein Structure:a chain of amino acids

Enzyme: Beef Ribonuclease

2o Protein StructureAlpha Helix

3o Protein StructureFolded Helix

Enzymes

• Biological catalysts that speed up metabolic reactions

• Globular proteins

• Can be reused.

• Name often ends in -ase.

• Act on chemicals called substrates.

Enzyme Specificity Examples

Enzyme Substrate

Amylase Amylose (starch)

Pepsin Protein

Lipase Lidpid (fat)

Nuclease Nucleic acid

Sucrase Sucrose (table sugar)

Lactase Lactose (milk sugar)

Enzyme Specificity

Lock and Key Model 1

• All enzymes have active sites.

• The lock is the enzyme

• The key is the substrate.

• Only the correct key (substrate) fits into the key hole (active site) of the lock (enzyme).

Lock and Key Model 2

Induced Fit Model

The enzyme changes shape on to fit the substrate only after binding to the substrate.

Enzymes as Catalysts

Enzymes lower the activation energy.

Speed of enzyme controlled reactions depends on

• Temperature

• pH

• Concentration

• Co-factors

Effect of Temperature

Effect of pH 1

Effect of pH 2

Effect of Substrate Concentration

Effect of Co-factors

Co-factor examples: Ca2+, Mg2+, Vitamin K, Vitamin B1, folic acid

Enzyme Inhibitors

Examples of inhibitors: mercury, cadmium, lead, arsenic

Cellular Respiration

C6H12O6 + 6O2 6H2O + 6CO2 + energy

ATP: Adenosine triphosphate

Hydrolysis of ATP

Respiration: Glycolysis (1)

Respiration: Glycolysis (2)

Conversion of pyruvate to Acetyl-CoA

Mitochondrion

Respiration: Kreb Cycle (matrix)

Respiration: Respiratory Chain (cristae lining)

• Each FADH2 produces 2ATP and regenerates FAD.

• Each NADH2 produces 2ATP and regenerates NAD.

• Hydrogen combines with oxygen to form water.

Anaerobic Respiration

• Without oxygen the respiratory chain stops so NAD and FAD are not regenerated.

• Pyruvate enters an anaerobic pathway to produce some ATP and regenerate some NAD.

Anaerobic RespirationLactic Acid Fermentation

Anaerobic RespirationEthanol Fermentation

Comparing Aerobic and Anaerobic Energy Yeilds

Yield ATP Yield Kilo joule

Aerobic Respiration

36 2880

Lactic Acid Fermentation

2 150

Ethanol Fermentation

2 210

Photosynthesis

light energy + 6H2O + 6CO2 C6H12O6 + 6O2

Photosynthesis Summary

Photosynthesis: Light Reactions

Photosynthesis: Calvin Cycle

Factors Affecting the Rate of Photosynthesis

• Light intensity• Carbon dioxide

concentration• Temperature

END