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