Module 2 definitions

• ACTIN: A thin type of protein filament found in a myofibril. Consists of two strands twisted around each other.
• ACTIVATION ENERGY: The minimum amount of energy needed to make a reaction take place. Enzymes provide an alternative pathway with a lower activation energy required for a substrate to change into a product.
• ACTIVE SITE: An area on an enzyme molecule where the substrate can bind.
• ACTIVE TRANSPORT: The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins.
• ADHESION: Water molecules are attracted to surfaces such as the walls of cells, vessels or tubes.
• ADP [ADENOSINE DI-PHOSPHATE]: A nucleotide consisting of the nitrogenous base, adenine covalently bonded to the pentose sugar ribose, [so forming adenosine] and two phosphate groups forming a short chain. ADP is formed from ATP during energy transfer in cells. The final phosphate group in ATP is removed by hydrolysis to release energy and inorganic phosphate.
• ALLELE: One of the alternative or different forms of the same gene e.g. in pea plants there is a gene for the colour of the seed pod. This gene has two different alleles, an allele which codes for green pods and another allele which codes for yellow pods.
• ALPHA GLUCOSE: A hexose monosaccharide with the formula C6H12O6. An isomer of beta glucose. The -OH group is below the carbon at position 1.
• ALPHA HELIX: A type of secondary structure of a protein. The polypeptide chain is coiled and held in place by hydrogen bonds. Hydrogen bonds form between the oxygen of the -C=O group of one amino acid and the hydrogen of the -NH group of an amino acid four places further along the chain.
• AMINO ACID: Molecules consisting of carbon, hydrogen, nitrogen and oxygen. They are monomers, that when joined together form proteins. Every amino acid has a central carbon atom to which are attached four different chemical groups. The amino [-NH2] group; carboxyl group [-COOH]; hydrogen atom [-H]; R group.
• AMYLOPECTIN: A component of starch. Consists of many alpha glucose molecules joined together in a chain by 1, 4 glycosidic bonds. It has short side branches of alpha glucose attached to the main chain by 1,6 glycosidis bonds.
• AMYLOSE: A component of starch. Consists of many alpha glucose molecules joined together by 1,4 glycosidic bonds. The chain is coiled into a helix.
• ANAPHASE: The centomeres divide and the newly separated chromatids are pulled by their centromeres to opposite poles of the cell. The spindle fibres shorten at both ends so pulling the chromatids apart.
• ANAPHASE: The centomeres divide and the newly separated chromatids are pulled by their centromeres to opposite poles of the cell. The spindle fibres shorten at both ends so pulling the chromatids apart.
• ANGIOSPERMS: A large group of higher plants that produce flowers and seeds with a testa or seed coat.
• ANTIPARALLEL: A term used to describe the opposite arrangement of the two strands of a double helix.The 5' prime end of one strand aligns with the 3' end of the other.
• ASEXUAL REPRODUCTION: A type of reproduction that does not involve the fusion of sex cells/gametes or a change in the number of chromosomes. Offspring are produced from a single individual and are genetically identical to the parent organism. E.g. vegetative propagation; parthenogenesis; budding; spore formation, fragmentation.
• ASEXUAL REPRODUCTION: A type of reproduction that does not involve the fusion of sex cells/gametes or a change in the number of chromosomes. Offspring are produced from a single individual and are genetically identical to the parent organism. E.g. vegetative propagation; parthenogenesis; budding; spore formation, fragmentation.
• ATP [ADENOSINE TRI-PHOSPHATE]: A nucleotide consisting of the nitrogenous base, adenine covalently bonded to the pentose sugar ribose, [so forming adenosine] and three phosphate groups forming a short chain. ATP is a compound that transfers energy within cells. It is the universal energy currency and used in metabolic processes, muscle contraction; active transport; exocytosis; activation of molecules.
• ATP HYDROLASE: An enzyme which catalyses the conversion of ATP and water to ADP, inorganic phosphate and energy. This is a hydrolysis reaction as water is used in the conversion of ATP to ADP.
• ATP SYNTHASE: An enzyme which catalyses the conversion of ADP and inorganic phosphate into ATP. This is a condensation reaction as water is removed in the process.
• BASEMENT MEMBRANE: A thin delicate membrane of protein fibres and polysaccharides separating an epithelium from underlying tissue.
• BENEDICT'S REAGENT: A blue alkaline solution of copper(II) sulfate. It is used to test for reducing sugars containing an aldehyde functional group (-CHO). When a reducing sugar is heated with Benedict's reagent, soluble copper (II) sulfate forms as insoluble precipitate of copper(I) oxide.
• BETA GLUCOSE: A hexose monosaccharide with the formula C6H12O6. An isomer of alpha glucose. The -OH group is above the carbon at position 1.
• BETA PLEATED SHEET: A type of secondary structure of a protein. The polypeptide chain folds in a concertina like way, with hydrogen bonds forming between the oxygen of a -C=O group of one amino acid in one sheet and the hydrogen of the -NH group of an amino acid in an adjacent pleated sheet.
• BINARY FISSION: A form of asexual reproduction in bacteria and some single celled eukaryotes such as Amoeba and Paramecium. During binary fission, the fully grown parent cell divides into two and each half becomes an independent organism.
• BINARY FISSION: A form of asexual reproduction in bacteria and some single celled eukaryotes such as Amoeba and Paramecium. During binary fission, the fully grown parent cell divides into two and each half becomes an independent organism.
• BIURET TEST: A chemcial test for the presence of amine groups and thus for the presence of proteins. Biuret reagent is added to the unknown substance where a change from blue to purple indicates the presence of proteins.
• CALIBRATE: To determine, rectify or mark the graduations of a measuring instrument. e.g. using a stage micrometer to determine the length of each divison on an eye piece graticule.
• CAMBIUM: Stem cell tissue in plants which produces xylem vessels and phloem sieve tubes. The cambium is an example of a meristem. There are meristems at the root and shoot tips.
• CAPSULE: A thick polysaccharide layer which can cover the outer layer of bacterial cell walls. The capsule prevents bacterial dessication; helps to resist phagocytosis by macrophages and provides protection against bacterial viruses and hydrophobic toxins such as detergents.
• CARDIAC MUSCLE: Found exclusively in the heart. Myogenic. Cardiac muscle cells appear striated under the microscope with many mitochondria. Cardiac muscle cells are connected by intercalated discs.
• CARRIER PROTEIN: A protein which spans the plasma membrane. A carrier protein combines with a specific molecule such as glucose, causing the carrier protein to change shape so that the molecule is released to the inside of the membrane.
• CARTILAGE: An example of connective tissue. It is composed of specialised cells called chondrocytes that produced an extracellular matrix consisting of collagen fibres, which stiffen and strengthen the tissue, and elastin fibres which give flexibility. The function of cartilage is to protect and strengthen. In mammals, it is found in synovial joints; rib cage; nose, ear, trachea and bronchi.
• CATALYST: A substance that increases the rate of a chemical reaction but does not become altered or changed during the reaction, so can be reused.
• CELL CYCLE: A sequence of changes during the lifespan of a cell, involving sequences of cell divisions separated by periods of cell growth. The cell cycle has three stages: interphase; nuclear division; cytokinesis. The length of the cell cycle varies for different types of cell e.g. bone marrow cells approx 18 hours; yeast cells 1.3-3 hours.
• CELL CYCLE: A sequence of changes during the lifespan of a cell, involving sequences of cell divisions separated by periods of cell growth. The cell cycle has three stages: interphase; nuclear division; cytokinesis. The length of the cell cycle varies for different types of cell e.g. bone marrow cells approx 18 hours; yeast cells 1.3-3 hours.
• CELL DIFFERENTIATION: The process by which a cell develops into a specialised cell with a specific function.
• CELL FRACTIONATION: The process used to break up cells and isolate their different organelles to study their structure and function.
• CELL RESPIRATION: Complex sequence of many enzyme controlled reactions that occur in cells and result in the release of energy, that is used to make adenosine triphosphate (ATP).