Cell Biology Glossary

antibody

A protein produced by the body's immune system in response of an invading substance (called antigen) or organism. The antibody specifically combines with the invader, which leads usually to its destruction.

autophagosome

A vesicle which encloses material from inside the cytoplasm such as spent organelles or other structures and polymers to be degraded

ATP

Adenosine triphosphate: a high energy compound used by the cell to provide activation energy for chemical reaction. ATP transfers a phosphate to the substance to activated and ATP itself is converted to ADP (Adenosine diphosphate). For example glucose can react with ATP to form glucose-6-phosphate and ADP. This activates glucose and in this activated form it is highly reactive, e.g. it can convert itself to fructose and other compounds. The cell has covert ADP back to ATP in a process which requires energy.

axon

the branched ending of the extended section of a neuron. If an electrical stimulus arrives at the axon it can trigger the release of a neurotransmitter which travels to a receptor of an adjacent cell causing a specific response

beta oxidation

A process by which fatty acids are converted into acetyl CoA . A fat molecule (triglyceride) contains 3 fatty acid residues. After hydrolysis by a lipase, the fatty acids enter the mitochondria, where they are oxidized to acetyl CoA. Assuming 18 carbon atoms per fatty acid, at total of 9 acetyl CoA (acetyl : has 2 carbons) can be formed (27 per triglyceride) . In addition the process yields 1 NADH and 1 FADH₂ per acetyl CoA formed.

cell wall

A rigid layer surrounding most bacterial cells, plant cells and some protists.

chromatin

Dense complex consisting of double helix DNA and histones. Sub-structures are nucleosomes, which condense into chromatin fibers. See your textbook for illustration.

chromosome

In eukaryotes a very dense complex consisting of double helix DNA and protein (histones). At the beginning of cellular division the amorphous chromatin condenses into the recognizable shape of chromosomes. Each chromosome as a centromer which joins the sister chromatids together and serves as an attachement for microtubules. See your textbook for illustration.

capsule

See glycocalyx

centromer

Constricted region of a chromosome which serves as a site for microtubule attachment

clathrin

A large protein, which forms a cage around a vesicle about to bud of from the Golgi or the plasma membrane. The formation of this cage helps the budding off process. Endocytosis is aided by the formation of a clathrin coat.

Coenzyme A

CoA is a vitamin like substance ( vertebrates cannot synthesize it) which can carry acetyl groups. Acetyl-CoA is the form in which carbon from glycolysis and fat degradation enters the tricarboxylic cycle.

cytoplasm

All cellular content enclosed by the plasma membrane, except the nucleus in eukaryotes and the nucleoid region in prokaryotes . See also cytosol below.

Cytosol

the fluid content of the cytoplasm (excluding the membrane bound organelles).

DNA

See Structure of DNA

endocytosis

Uptake of particles of food by the cell through invagination of the exterior side of the plasma membrane and formation of a vesicle which buds off the inside of the membrane , diffusing into the cytoplasm .

Endosome

A vesicle formed by fusion of several other vesicles which were imported into the cytoplasm by receptor mediated endocytosis .

Enzymes

Enzymes are proteins which act as catalysts in cellular chemical reactions. They lower the activation energy, so that chemical reactions can occur at room temperature. All cellular reactions are controlled by enzymes.

eukaryotic

A eukaryotic cell has nucleus and cellular organelles such as mitochondria, rough ER smooth ER, Golgi etc.

flagella

Bacterial flagella are long, rotating filaments enabeling the bacteria to move in any direction. A flagellum consist of three structural units: a basal body anchored in the cell wall and cell membrane and a filament , consisting of the polypeptide flagellin, which is attached to the basal body via a layer of proteins called hook.

fimbria and pili

Thin filaments protruding from the cell wall of gram negative bacteria. Unlike flagella they don't serve for motility but they are used to attach bacteria to surrounding structures.

gene

A segment of DNA which encodes a m-RNA (which is translated into a protein), a t-RNA or a r-RNA . This segment of the DNA may include control sequences for the expression of the gene.

glutathion

Tripeptide : H₃N-CH(COO^-)-CH₂-CH₂-CO-NH-Cys-Gly , which has two major functions. Prevent formation of S-S bonds in the cytosol and promote S-S formation in the RER. Glutathion is the major SH containing molecule in eukaryotic cells

glycocalyx

Bacterial glycocalyx is a sticky polymer which surrounds the bacterial cell wall. It consist of polysaccharides and polypeptides. It can be loosely attached to the cell wall (slime layer) or firmly attached (capsule)

haploid

Having only one copy of each chromosome. Sperm or egg cells (gametes) are haploid, compared to somatic cells which are diploid is located.

heterozygous

Having two different alleles of the same gene.

homologous chromosome

One of two copies of a chromosome . One copy is derived from the male parent and the other copy is derived from the female parent

homozygous

Having two identical alleles of the same gene.

locus

The position on a chromosome where a gene is located.

lysosome

An organelle that contains hydrolytic enzymes, which can degrade biopolymers such as DNA, RNA (nucleases), polysaccharides such as glycogen and starch (glycosidases), protein (proteases), cell wall components and biomembrane components (phosphatases).

lysosomal enzymes

Hydrolytic enzymes that can degrade any type of biological polymers. See also lysosome .

meiosis

Process of cellular division which produces egg or sperm cells. After replication an initially diploid cell undergoes two divisions, resulting in four haploid daughter cells.

mitosis

Process of cellular division which maintains the number of chromosomes. Cell proliferation proceeds via mitosis.

m-RNA

Messenger RNA is synthesized in the nucleus in a process called transcription using a DNA segment as a template. m-RNA encode for proteins, which are synthesized on ribosomes using the m-RNA as a blue print for the amino acid sequence.

neurotransmitter

A substance released from the axon terminal of a nerve cell (neuron) which travels across the synaptic cleft to bind to a specific receptor. If this is a muscle cell receptor, muscle contraction will be initiated.

nucleoid

In prokaryotes a region of the cell which contains chromosomal DNA . The nucleoid is physically apart from other cytoplasmic components. Eukaryotes have a nucleus which contains the chromosomal DNA.

nucleotide

Basic building block molecule of DNA or RNA. Consists of ribose or deoxyribose, nucleic acid base and phosphate. See your textbook for an illustration

nucleus

The nucleus of eukaryotes is a membrane bound organelle, which contains the chromosomal DNA . Prokaryotes do not have a nucleus but a nucleoid region

peptidoglycan

Peptidoglycan is a bacterial cell wall polymer which consists of a N-acetylglucosamine and N-acetylmuraminc acid sugar backbone, which is crosslinked by short peptide chains. The amino acids occur in their D and L configuration. In the biosynthesis of peptidoglycan the antibiotic Penicillin inhibits the cross linking reaction between D-Ala and the Gly peptide chain, thus preventing the completion of the cell wall assembly. No longer protected by its cell wall the bacteria is not viable anymore.

phagosome

A vesicle which encloses material from coming from the outside of the cell by endocytosis .

prokaryotic

A prokaryotic cell has no nucleus and no cellular organelles. Bacteria are prokaryotes.

protists

respiration

The process of generating energy from the oxidation of organic compounds, with the electrons transferred to oxygen as the final electron acceptor. Respiration includes TCA, electron transport chain, proton gradient and ATPase, see lecture notes.

ribosome

Site of protein synthesis. Ribosomes consist of small and large ribosomal RNA segments and protein.

r-RNA

Ribosomal RNA is a basic building block for ribosomes Together with protein they make up ribosomes.

teichoic acid

Cell wall constituent of gram positive bacteria. Teichoic acid is a polymer consisting of repeating units of glycerol or ribitol , linked together by phosphate groups.

t-RNA

Transfer RNA is a form of RNA that binds to amino acids. There are different t-RNAs for every protein amino acid. The amino acid t-RNA complex travels to ribosomes where the amino acids are needed for protein assembly.