Module 2 Foundations in Biology OCR A Level Definitions Part 1

Actin

Protein forming the contractile microfilaments of the cytoskeleton

Activation energy

Energy required for a reaction to start

Active site

An area in an enzyme molecule which has a shape complementary to the shape of a specific substrate molecule

Active transport

The movement of particles across a plasma membrane against a concentration gradient (from an area of low concentration to high concentration), requiring energy.

Adenine

A purine, capable of forming two hydrogen bonds

Adhesion

When water molecules are attracted to other materials e.g. the sides of a tubeA

ADP

A nucleotide comprised of a base, a sugar and two other phosphate gorups

Alleles

Different forms/versions of a gene

Amine group

Part of an amino acid molecule comprised of a nitrogen atom and two hydrogen atoms

Amino acid

Monomers of a polypeptide

Amylopectin

Branched polysaccharide in starch formed from 1-4 and 1-6 glycosidic bonds

Amylose

Unbranched polysaccharide in starch formed from 1-4 glycosidic bonds.

Anabolic

Chemical reactions required for growth

Anaphase

Stage in mitosis in which chromatids are pulled to opposite poles of the cell by shortening spindle fibres

Anion

Negatively charged ion

Anticodon

Three bases on a tRNA molecule complementary to three bases (codon) on mRNA

Antiparallel

Two strands in DNA, running in opposite directions

Antisense strand

In protein synthesis, the strand which acts as a template strand during transcription. Sometimes called the non-coding strand

Artefacts

Structures produced as part of the preparation process of microscope slides. Common in electron microscopy.

Asexual reproduction

Type of reproduction resulting in genetically identical offspring.

ATP

A nucleotide comprised of a base, a sugar and three phosphate groups. Is an immediate energy source for the cell.

Benedict’s reagent

Chemical used to test for reducing sugars

Betalain

Red pigment found in beetroot

Bilayer

Formed by phospholipids when placed in solution

Biosensor

Devices which use biological components to determine the presence and concentration of molecules such as glucose

Bonding

Joining of two molecules togeth

Bone marrow

Part of the body in which red and white blood cells are produced from adult stem cells

Bulk transport

A form of active transport involving molecules which are too large to move through channel or carrier proteins.

Calibration

The proess of comparing an eyepiece graticule to a stage micrometer

Carbohydrate

Molecules containing only carbon, hydrogen and oxygen, usually in the ratio Cx(H2O)y.

Carboxylic acid group

Part of an amino acid containing a hydroxyl group (OH) and a double bond to an oxygen atom.

Carrier protein

Membrane proteins involved in transport of substances through the membrane

Catabolic

Reactions in which chemicals are broken down

Cation

A positively charged ion.

Cell cycle

The sequence of events occurring in a cell resulting in nuclear division and formation of daughter cells.

Cell signalling

Complex system of intercellular communication

Cell wall

Rigid structure made of cellulose or peptidoglycan. Found in prokaryotic cells and plant cells, but not animals.

Cellulose

Carbohydrate that makes up plant cell walls. Made of beta glucose joined by 1-4 glycosidic bonds.

Centriole

Component of cytoskeleton made of microtubules. Two of them form the centrosome which is involved in spindle fibre formation.

Centrioles

Part of the cytoskeleton composed of microtubules and involved in cell division.

Centromere

Region where two chromatids form.

Channel proteins

Membrane proteins that provide a hydrophilic channel through the membrane.

Checkpoints

Control mechanisms which ensure the the cell cycle proceeds as it should.

Chiasmata

Points at which chromatids break and rejoin during crossing over in meiosis.

Chloroplast

Contain stroma and thylakoids stacked as granum. Site of photosynthesis.

Cholesterol

A type of lipid involved in cell membrane structure, formed of a complex ring structure

Chromatids

Identical copies of DNA held together at a centromere

Chromatin

Uncondensed DNA in a complex with histone proteins

Chromosome

Condensed and coiled DNA forms these structure, visible during cell division under a microscope.

Cilia

Hair-like extensions protuding from the cell.

Ciliated epithelium

A tissue found in the tubes of the respiratory system

Cleavage furrow

During cytokinesis in an animal cell, this forms around the middle of the cell and causes the plasma membrane to be pulled inwards.

Codon

Three bases on mRNA which provide the code for a particular amino acid in the resulting polypeptide chain

Coenzyme

Organic cofactors of enzymes

Cofactor

Molecules required to enable an enzyme to work

Cohesion

When water molecules are attracted to each other, due to hydrogen bonding

Collagen

A fibrous protein. Connective tissue found in skin, tendons, ligaments and nervous system.

Colorimeter

Device used to measure absorbance or transmission of light in coloured solution.

Compartmentalisation

Formation of separate membrane-bound areas in a cell

Competitive inhibitor

A molecule with a similar shape to the substrate of an enzyme and blocks the substrate from entering the active site.

Complementary base pairing

When certain bases are able to pair up e.g. T with A and G with C.