Cell Theory:
All organisms are composed of cells, and new cells arise from other cells.
Prokaryotes
DNA is in a circular loop, lack membrane-bound organelles and microtubules. Cell wall is present and flagella are different to Eukaryotes. 3 Groups: Bacilli, cocci and spirilla.
Eukaryotes
Nucleus is separated from cytoplasm by 2 layered nuclear envelope. DNA organised into chromosomes with other membrane-bound organelles present. Microtubules are present and sexual reproduction is widespread.
Plant Cells
Chlorophyll enables plants to convert water and CO2 into sugars and carbohydrates. Plants have a rigid cell wall, central vacuole, plasmodesmata and chloroplasts. They lack centrioles, lysosomes, cilia and flagella.
Animal Cells:
Typical eukaryotic cell, enclosed by plasma membrane but lacking a cell wall, unlike plant & fungi cells.
Nucleus
Controls cell activity through DNA by directing protein synthesis and cell division. The nucleus is separated from the cytoplasm by a two-layer nuclear envelope and is the control centre of the eukaryotic cell.
Chromosomes
The organisation of a cell’s DNA
Organelle
Membrane bound region of the cell designed for a specific purpose. Make up cells and have one or more special purposes which contribute to the overall functioning of the cell.
Cell Specialisation
During the development of organisms, cells differ from one another by their shape, type and number of organelles present.
Cell/Plasma Membrane
Encloses the cell and forms a boundary between the cell’s environment and the content of the cell. Cell materials entering or leaving the cell must pass through this membrane which is composed of thin layers of protein and fat molecules. Phospholipid bilayer, in which proteins are embedded; surrounded by cell contents.
Endoplasmic Reticulum
Membranous structure with connections to both the nuclear and cell membranes. Involved in the production, storage and transport of substances within the cell. Lipids and steroids are produced in the smooth ER, while proteins are synthesised on ribosomes of rough ER.
Ribosome
Composed of RNA; produced in the nucleus and found on rough ER or free in the cytoplasm; site of protein synthesis in cell.
Cytoplasm
Jelly that supports the organelles; includes the cell contents excluding the nucleus.
Mitochondria
Membrane bound, cellular organelle; has inner membrane forming folds (cristae) on which are found enzymes for aerobic respiration, and a fluid matrix. Found in the cytoplasm of eukaryotic cells, in animal cells they are the site of respiration where oxygen and nutrients are converted into energy.
Chloroplast
Plastid found in green plants, containing chlorophyll on membranous grana and enzymes in liquid stoma; photosynthetic organelle.
Vacuole
Cellular inclusion; small in animals (food storage and/or digestion); large in plants (storage and osmotic control).
Cell Wall
Rigid structure surrounding the cells of some organisms composed of cellulose in plants.
Permeability
Ability of a membrane to allow a substance to diffuse through it. Many substances diffuse readily across membranes from areas of high concentration to low.
Passive Transport
Movement of materials in and out of the cell without the expenditure of energy.
Simple Diffusion
Unaided movement of molecules or ions across a differentially permeable membrane along a concentration gradient.
Osmosis
Movement of water from an area of low solute concentration to a region of high solute concentration through a selectively permeable membrane to counteract the differences in concentration.
Active Transport:
Movement of materials into and out of the cell, usually against a concentration gradient, requiring cellular energy
Endocytosis
When a substance is enclosed within a vesitcle and incorporated into the cell. If solid particles are absorbed the process is called phagocytosis, if the materials are composed of liquid/small particles it is known as pinocytosis.
Exocytosis
The active process of extrusion or secretion where unwanted materials are removed into the surrounding environment. This occurs by active transport against the cell membrane by the formation of cytoplasmic vesticles.
Mitosis
Nuclear division resulting in daughter cells with chromosomes of exactly the same types and number as in the parent cell.
Mitosis | |
Interphase | Chromosomes are copied |
Chromosomes appear as threadlike coils (chromatin) at the start, but each chromosome and its copy change to sister chromatids at the end of the phase | |
Prophase | Mitois begins (Cells begin to divide) |
Centrioles (or poles) appear and begin to move to opposite ends of the cell | |
Spindle fibres form between the poles | |
Metaphase | Chromatids (pairs of chromosomes) attach to the spindle fibres |
Anaphase | Chromatids separate and begin to move to opposite ends of the cell |
Telophase | 2 New nuclei formed |
Chromosomes appear as chromatin (threads rather than rods) | |
Mitosis ends | |
Cytokinesis | Cell membrane moves inward to create 2 daughter cells, each with its own nucleus with identical chromosomes |
Enzymes
Organic catalysts which are produced by living cells and change the rate of chemical reactions in living organisms. Main function is to lower the activation energy required to start a chemical reaction and they are only needed in small quantities. Enzymes are specific, only catalysing one specific chemical reaction.
Active Site
Portion of an enzyme in contact with the substrate; at this point it will have a specific shape which corresponds to the shape of at least a portion of the substrate molecule.
Anabolic
Chemical reactions in which large molecules are built up, usually with a net output of energy.
Catabolic
Chemical reactions in which large molecules are broken down into smaller ones, usually accompanied by the release of energy.
Substrate:
Substance being changed; by either being broken down or built up by an enzyme.
Activation Energy
Energy required to start a reaction, with the change in energy (released or absorbed) from the initial state to the final state.
Exergonic
Energy is released during the reaction
Endergonic
Energy is higher in the final state than it was initially.
Lock & Key Theory
The function of an enzyme depends upon its shape. The substrate move into a designed part of the enzyme that fits them, and then lift off to result in the formation of the product.
Induced Fit Mechanism
Interaction between the substrate and the enzyme where the shape of the enzyme is changed to accommodate the substance it reacts with.
Competitive Inhibitors
Have a similar nature to the natural substrate and compete for the active site on the enzyme. The success of the inhibitor binding to the active site depends upon its relative concentration in relation to the natural substrate. Therefore the condition is reversible if there is an increase in substrate production.
Non-Competitive Inhibitors
Reduce enzyme activity by distorting the enzyme by binding to some site other than the active site.
Activators:
May be necessary to complete the structural relationship between the activation site and the substrate.
Enzyme Action
Temperature can destroy enzymes by denaturing them, where linkages between parts of the coiled protein molecules come apart affected its ability to interact with the enzyme. PH affects enzyme function.
Enzyme Factors
The greater the concentration of enzymes, the greater the rate of reaction. Substrate concentration limits the rate of enzyme action because once all the enzyme is committed to a reaction, it is unable to proceed any faster.
Blackman’s Law
A reaction is only as fast as the slowest step in that reaction.
Respiration
Energy is released through cell respiration, which involves the oxidisation of sugar in a series of steps each controlled by an enzyme. The energy is stored in the ATP molecule. Some steps in the process are endergonic (require energy) while others are exergonic (release energy) in the formation of ATP. There is an overall gain of 32 molecules of ATP during the respiration of one glucose molecule. C6H12O6 + 6O6 = 6CO2 + 6H2O + Energy.
ATP
Energy released from food cannot be used directly by the body; instead the energy is used to create molecules of ATP, which is a temporary store of energy which can be released when required. ATP is formed from the related substance ADP by the process of respiration which is used to bend the third phosphate group. This creates an energy rich phosphate bond which is easily broken when energy is required. ATP is renewable and is regenerated by adding a phosphate group to ADP by a catabolic reactions within the cell.
ATP Advantages
Uses up some of the energy that would otherwise be lost as heat as the respiratory enzymes broke down food. This increases the efficiency of respiration and the energy can be released from ATP in an instant instead of going through the 50 steps of respiration. ATP delivers energy in controlled amounts – each phosphate releases 34 KJ or 1 mole of ATP. Energy rich bonds can be transferred from ATP to other substances without any loss of energy, converting these substances from a relatively inert state to a highly reactive one.
Stages of Respiration
Glycolysis, the Krebs Cycle and the Electron Transfer Chain.
Glycolysis
Occurs in the cytoplasm and is the anaerobic process where glucose is split in a series of steps involving the energy from 2 ATP molecules. Each glucose molecule is converted into 2 pyruvic acid molecules with an overall gain of 2 ATP molecules. If there is no oxygen present then the pyruvic acid is converted into lactic acid in animals and ethyl alcohol in plants. If oxygen is present then the pyruvic acid and the oxygen enter the mitochondria where it is broken down completely to CO2, water and 32 molecules of ATP by the Krebs (citric acid) Cycle and the electron transfer chain. The oxygen removes the hydrogen released by the Krebs Cycle.
Respiration | |
Glycolysis | Splitting of glucose |
Occurs in the cytoplasm | |
Anaerobic process | |
Involves the energy from 2 ATP molecules | |
Each glucose molecule is converted into 2 pyruvic acid molecules | |
There is a gain of 2 ATP molecules | |
No Oxygen | Pyruvic acid is converted into lactic acid or ethyl alcohol and CO2 |
Oxgen | Aerobic respiration |
Pyruvic acid and oxygen enter the mitochondria | |
Inner membrane is permeable to ions so an electrochemical gradient is established | |
This membrane contains the enzymes responsible for ATP | |
The matrix contains ribosomes, DNA and enzymes which assist respiration | |
The pyruvic acid is broken down completely into CO2, water and 34 molecules of ATP by the krebs cycle and electron transfer chain | |
| The oxygen removes the hydrogen released by the Kreb cycle | |
Acetyl CoA
Converted fats and amino acids which are used as energy sources for respiration and enter the Krebs Cycle. Fats are broken down for respiration when there is no more glycogen (in animals) or starch (in plants) available to convert into glucose. When the organism’s fat reserves are depleted, it will convert proteins.
Aerobic Respiration | |
Glycolysis | 6-C glucose molecule is converted into 2 3-C pyruvic acid molecules |
4 ATP molecules are formed = 2 ATP net gain | |
4 hyrogen ions and 8 electrons transfer to co-enzyme NAD+ = 2 NADPH plus 2 hydrogen ions | |
Each pyrivic acid molecule is converted to acetyl CoA | |
This process creates 4 more molecules of NADPH | |
The acetyl CoA enters the Krebs Cycle | |
Krebs Cycle | Formation of citric (6-C) acid by the combination of acetyl CoA with 4-C acid |
It is then broken down to produce 8 Hydrogen atoms which form: | |
6 NADPH | |
1 FADH2 | |
1 ATP | |
2 CO2 | |
Orginal 4-C acid for each acetyl CoA | |
2 of these molecules are formed as a result of the breakdown of 1 glucose molecule | |
Krebs cycle output: | |
12 NADPH | |
2 FADH2 | |
4 CO2 | |
Altogether 6 H2O molecules are used in this reaction | |
Electron Transfer Chain | 24 Hydrogen electrons (4 from glycolysis, 4 from the formation of acetyl CoA and 16 from the Krebs Cycle and used in NADH and FADH2) are used in the electron transfer chain |
12 pairs of electrons are transferred from these molecules (NADH & FADH2) to a co-enzyme chain | |
12 pairs of hydrogen ions (H+) are released | |
The electrons which have a high energy potential release bundles of energy as they pass from 1 co-enzyme to the next | |
This energy converts 32 ADP + 32 P to 32 ATP molecules | |
| The low energy electrons join with hydrogen ions and oxygen to form 12 water molecules at the end of the chain | |
Anaerobic Respiration
Some organisms derive sufficient energy by this process, such as complete anaerobes which never require oxygen or partial anaerobes which thrive in oxygen but can survive without it. There is a net gain of 2ATP and lactic acid (in animals) or ethyl alcohol and CO2 (in plants and fungi).
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