Cambridge International AS & A Level Biology: Cell Structure and Biological Molecules

Comprehensive vocabulary flashcards covering cell structure, organelles, microscopy, biological molecules, enzymes, and cell membranes based on the Cambridge International AS & A Level Biology coursebook.

cell

The basic unit of all living organisms; it is surrounded by a cell surface membrane and contains genetic material (DNA) and cytoplasm containing organelles.

organelle

A functionally and structurally distinct part of a cell, e.g. a ribosome or mitochondrion.

nucleus

A relatively large organelle found in eukaryotic cells, but absent from prokaryotic cells; it contains the cell's DNA and therefore controls the activities of the cell and is surrounded by two membranes known as the nuclear envelope.

eukaryote

An organism whose cells contain a nucleus and other membrane-bound organelles.

prokaryote

An organism whose cells do not contain a nucleus or any other membrane-bound organelles.

cell surface membrane

A very thin membrane (about $7\,nm$ diameter) surrounding all cells; it is partially permeable and controls the exchange of materials between the cell and its environment.

chromatin

The material of which chromosomes are made, consisting of DNA, proteins and small amounts of RNA; visible as patches or fibres within the nucleus when stained.

chromosome

In the nucleus of the cells of eukaryotes, a structure made of tightly coiled chromatin (DNA, proteins and RNA) visible during cell division.

nucleolus

A small structure found inside the nucleus which functions to manufacture ribosomes using the information in its own DNA.

protoplasm

All the living material inside a cell (cytoplasm plus nucleus).

cytoplasm

The contents of a cell, excluding the nucleus.

mitochondrion

The organelle in eukaryotes in which aerobic respiration takes place; it is usually about $1\,\mu m$ in diameter and surrounded by an envelope.

cell wall

A wall surrounding prokaryote, plant and fungal cells; the wall contains a strengthening material which protects the cell from mechanical damage, supports it and prevents it from bursting by osmosis.

plasmodesma

A pore-like structure found in plant cell walls; they line up to form tube-like pores allowing the controlled passage of materials from one cell to the other.

vacuole

An organelle found in eukaryotic cells; plant cells typically features a large, permanent central one for storage and osmotic regulation.

tonoplast

The partially permeable membrane that surrounds plant vacuoles.

chloroplast

An organelle, bounded by an envelope (i.e. two membranes), in which photosynthesis takes place in eukaryotes.

photosynthesis

The production of organic substances from inorganic ones, using energy from light.

grana

Stacks of membranes known as thylakoids inside a chloroplast.

microvilli

Small, finger-like extensions of a cell which increase the surface area of the cell for more efficient absorption or secretion.

nuclear envelope

The two membranes, situated close together, that surround the nucleus; the envelope is perforated with nuclear pores.

nuclear pores

Pores found in the nuclear envelope which control the exchange of materials, e.g. mRNA and ribosomes, between the nucleus and the cytoplasm.

endoplasmic reticulum (ER)

A network of flattened sacs called cisternae running through the cytoplasm of eukaryotic cells; continuous with the outer membrane of the nuclear envelope.

ribosome

A tiny organelle found in large numbers in all cells; eukaryotic ribosomes are 80S (about $25\,nm$ diameter) while prokaryotic ribosomes are 70S (about $20\,nm$).

Golgi apparatus

An organelle found in eukaryotic cells consisting of a stack of flattened sacs (cisternae), constantly forming at one end and breaking up into Golgi vesicles at the other.

Golgi vesicles

Vesicles that carry contents to other parts of the cell or to the cell surface membrane; the Golgi apparatus chemically modifies these molecules, such as adding sugars to proteins to make glycoproteins.

lysosome

A spherical organelle containing digestive (hydrolytic) enzymes and having destructive functions such as removal of old cell organelles.

cristae

Folds of the inner membrane of the mitochondrial envelope on which are found stalked particles of ATP synthase and electron transport chains.

ATP (adenosine triphosphate)

The molecule that is the universal energy currency in all living cells; the purpose of respiration is to make ATP.

microtubules

Tiny tubes made of a protein called tubulin; they have functions including cell support, determining cell shape, and forming the spindle during nuclear division.

centriole

One of two small, cylindrical structures made from nine triplets of microtubules, found just outside the nucleus in animal cells in the centrosome.

centrosome

The main microtubule organising centre (MTOC) in animal cells.

cilia

Whip-like structures projecting from the surface of many cells with a '9 + 2' arrangement of microtubules, causing locomotion or fluid movement.

peptidoglycan

A polysaccharide combined with amino acids, also known as murein, which makes the bacterial cell wall more rigid.

plasmid

A small circular piece of DNA in a bacterium (not its main chromosome); often contains genes providing resistance to antibiotics.

virus

A very small ($20-300\,nm$) infectious particle which can replicate only inside living cells; consists of DNA or RNA surrounded by a protein coat (capsid).

macromolecule

A large molecule such as a polysaccharide, protein or nucleic acid.

polymer

A giant molecule made from many similar repeating subunits (monomers) joined together in a chain.

monomer

A relatively simple molecule used as a basic building block for the synthesis of a polymer.

condensation reaction

A chemical reaction involving the joining together of two molecules by removal of a water molecule.

hydrolysis

A chemical reaction in which a chemical bond is broken by the addition of a water molecule.

monosaccharide

A molecule consisting of a single sugar unit with the general formula $(CH_2O)_n$.

disaccharide

A sugar molecule consisting of two monosaccharides joined together by a glycosidic bond.

glycosidic bond

A C-O-C link between two sugar molecules formed by a condensation reaction.

polysaccharide

A polymer whose subunits are monosaccharides joined together by glycosidic bonds, such as starch, glycogen or cellulose.

triglyceride

A type of lipid formed when three fatty acid molecules combine with glycerol via ester bonds.

peptide bond

The covalent C-N link joining neighbouring amino acids together in proteins, formed by a condensation reaction.

primary structure

The sequence of amino acids in a polypeptide or protein.

secondary structure

The structure of a protein molecule resulting from regular coiling or folding of the amino acid chain, such as an $\alpha$-helix or $\beta$-pleated sheet.

tertiary structure

The compact structure of a protein molecule resulting from the precise three-dimensional coiling of the chain of amino acids.

quaternary structure

The three-dimensional arrangement of two or more polypeptides, or a polypeptide and a non-protein component like haem, in a protein molecule.

haemoglobin

The red pigment in red blood cells; a globular protein made of four polypeptides each containing a haem group with an iron atom.

collagen

The main structural protein of animals; an insoluble fibrous protein with high tensile strength featuring a triple helix structure.

enzyme

A protein produced by a living organism that acts as a biological catalyst by reducing activation energy.

active site

An area on an enzyme molecule where the substrate can bind.

induced-fit hypothesis

A hypothesis for enzyme action where the enzyme changes shape slightly as the substrate enters the active site to ensure a perfect fit.

activation energy

The energy that must be provided to make a reaction take place; enzymes reduce this required energy.

Vmax

The theoretical maximum rate of an enzyme-controlled reaction, obtained when all the active sites of the enzyme are occupied.

Michaelis-Menten constant (Km)

The substrate concentration at which an enzyme works at half its maximum rate ($\frac{1}{2}V_{max}$); used as a measure of enzyme affinity.

competitive inhibition

When a substance reduces enzyme activity by competing with substrate molecules for the active site.

non-competitive inhibition

When a substance reduces enzyme activity by binding to a site other than the active site, changing the enzyme's shape.

fluid mosaic model

The accepted model of membrane structure in which protein molecules are free to move about in a fluid bilayer of phospholipid molecules.

cholesterol

A small lipid-related molecule in animal membranes that gives stability and flexibility while reducing fluidity.

cell signalling

The molecular mechanisms by which cells detect and respond to external stimuli, involving communication between cells.

ligand

A biological molecule which binds specifically to another molecule, such as a cell surface membrane receptor, during signalling.

transduction

The process during cell signalling of converting a signal from one method of transmission to another.

diffusion

The net movement of a substance from a region of higher concentration to lower concentration down a concentration gradient due to random motion.