Cells

anticodon - on the tRNA, a complementary three nucleotide site which recognizes and binds to a specific codon on the mRNA during protein synthesis.

base pairing rule - the way in which nucleotide bases chemically pair up in complementary nucleic acid chains of DNA or DNA/RNA. In general, A pairs with T in DNA and U in RNA; C pairs with G.

cell membrane - the part of the cell which separates the external environment from the cytoplasm; cell membranes have hydrophilic external surfaces and hydrophobic interiors.

cell wall - in plant cells, a tough, rigid structure made up of cellulose which is outside of the cell membrane; provides physical support and helps cells resist osmotic pressure.

cellular respiration - the intracellular, energy-producing process by which a cell obtains oxygen, distributes it to the mitochondria, uses it for oxidation of 6-carbon sugar and gives off carbon dioxide

chloroplast - an organelle present in algae and plant cells that contains chlorophyll and is involved in photosynthesis

codons - three nucleotide sequences in RNA which specify one amino acid (to be linked into a protein which is being synthesized).

complementary - with respect to nucleic acids, complementary means that one strand of nucleic acid (DNA or RNA) can pair with and serve as a template for its complementary strand; complementary strands are related by the base-pairing rules: A pairs with T or U and C pairs with G.

cytoplasm - gel-like substance in which all cellular components outside the nucleus are immersed.

cytoskeleton - protein lattice structure which gives shape to our cells.

DNA - deoxyribonucleic acid; the double-helical molecule that stores the genetic information in cells. A gene is a section of a DNA strand that codes for a produce (RNA and/or protein).

enzyme - a protein which can catalyze (increase the rate of) a chemical reaction inside of the cell.

Golgi apparatus - an organelle in the cytoplasm that packages proteins and carbohydrates into vesicles for export from the cell.

mitochondrion - organelle where final cellular respiration steps takes place (initial steps occur in the cytoplasm) and ATP is generated for use throughout the cell

nucleotides - the building blocks of DNA and RNA. The four nucleotides which make up DNA are adenine (A), cytosine (C), guanine (G), and thymine (T); the four nucleotides which make up RNA are adenine (A), cytosine (C), guanine (G), and uracil (U).

nucleus - organelle which contains the DNA, organized into chromosomes; site of mRNA synthesis from DNA.

organelles - membrane-bound structures found inside the cell cytoplasm.

peptide bond - a chemical bond linking two amino acid residues within a polypeptide; during protein synthesis, the peptide bond forms between two amino acids which are held side by side on the ribosome.

ribosome - subcellular structures (typically thousands per cell) that provide sites for protein synthesis; occur in cytoplasm and on rough endoplasmic reticulum.

RNA - ribonucleic acid; a single-stranded nucleic acid molecule involved in the creation of proteins directed by genes.

RNA polymerase - an enzyme which helps synthesize mRNA by transcribing the nucleotide sequence in DNA.

rough endoplasmic reticulum (RER) - a system of membranous tubes and sacs containing ribosomes which function in the manufacture of membrane-bound proteins.

selectively permeable - the characteristic of allowing only certain substances from the outside environment to enter the cell. The cell membrane and the membranes of organelles are selectively permeable.

smooth endoplasmic reticulum (SER) - a system of membranous tubes and sacs that functions in lipid synthesis.

subcellular structure - structures found in cells that are not enclosed in a membrane such as cytoskeleton, chromosome, and ribosomes.

transcription - the formation of RNA from a single strand of a DNA molecule; the process is catalyzed by the enzyme RNA polymerase.

transfer RNA (tRNA)- a small RNA molecule that "translates" a codon in mRNA by bringing in its corresponding amino acid during protein synthesis.

vacuole - large organelle in plant cells that contains water, often having dissolved pigments, waste materials, or other substances