AP BIO UNIT 5

DNA and Protein Synthesis

A site

The “aminoacyl tRNA” binding site on a ribosome during translation — it receives the charged tRNA carrying the next amino acid.

aminoacyl-tRNA

A tRNA molecule that is “charged” (i.e., covalently bound) with its corresponding amino acid, ready to add that amino acid to a growing polypeptide chain.

aminoacyl-tRNA synthetase

The enzyme that attaches the correct amino acid onto a specific tRNA (charging the tRNA) in preparation for translation.

base pair 

Two nitrogenous bases in DNA (or RNA) connected by hydrogen bonds in a complementary fashion (e.g., A-T in DNA, A-U in RNA, G-C).

centrioles

Cylindrical structures in animal cells composed of microtubules, playing a role in organizing the spindle fibers during cell division.

centromere 

The region of a chromosome where the two sister chromatids are most tightly attached; also the site where the kinetochore forms.

complementary 

Refers to the matching of base sequences in nucleic acids (e.g., one strand is complementary to the other because of base-pairing rules).

daughter cells

The two (or more) cells that result from the division of a parental (mother) cell (e.g., after mitosis or meiosis).

DNA polymerase

The two (or more) cells that result from the division of a parental (mother) cell (e.g., after mitosis or meiosis).

E site

The “exit” site on the ribosome during translation: after a tRNA has donated its amino acid and moved through the P site, it moves to the E site and exits.

exons

The expressed sequence segments of a eukaryotic gene that remain in the mature mRNA after splicing and encode portions of the final protein.

fertilization

The process by which two gametes (e.g., sperm + egg) fuse, combining their genetic material to form a zygote.

frameshift mutation

A mutation (insertion or deletion) of a nucleotide in DNA that shifts the reading frame of the codons, typically altering many downstream amino acids and often causing a nonfunctional protein.

Gene

A unit of heredity; a sequence of DNA that codes for a functional product (RNA or protein) and is passed from one generation to the next.

genetic code

The set of rules by which the nucleotide sequence of an mRNA is translated into the amino acid sequence of a protein; it includes codon-to-amino acid correspondences.

helicase

The enzyme that unwinds and separates the two strands of DNA at the replication fork during DNA replication.

hereditary

Pertaining to traits or genetic information passed from parent to offspring.

initiation

The first phase of a process (e.g., of transcription or translation): in translation, assembly of the ribosome, mRNA, and first tRNA; in transcription, binding of RNA polymerase to promoter and beginning RNA synthesis.

introns

Non-coding segments of a eukaryotic gene that are transcribed into the pre-mRNA but are removed during RNA splicing so they do not appear in the mature mRNA.

kinetochore

A protein complex assembled on the centromere of each chromatid; it attaches chromatids to spindle microtubules during cell division.

ligase

An enzyme that connects two fragments of DNA (or RNA) by forming a phosphodiester bond; in replication, DNA ligase connects Okazaki fragments.

nondisjunction

The failure of homologous chromosomes (in meiosis I) or sister chromatids (in meiosis II or mitosis) to separate properly during cell division, leading to abnormal chromosome numbers.

nuclease

An enzyme that cuts (hydrolyzes) the phosphodiester bonds between nucleotides in nucleic acids (DNA or RNA).

nucleosides

A molecule made of a nitrogenous base plus a sugar (ribose or deoxyribose); lacks the phosphate groups found in nucleotides.

nucleotides

The basic building blocks of nucleic acids: composed of a nitrogenous base, a sugar (ribose or deoxyribose), and one or more phosphate groups.

Okazaki fragments

Short newly synthesized DNA fragments formed on the lagging strand during DNA replication; later joined by DNA ligase.

operator

A regulatory DNA sequence (in prokaryotes) between the promoter and the genes of an operon where a repressor can bind to block transcription.

P site 

The “peptidyl-tRNA” binding site on a ribosome during translation; tRNA at the P site holds the growing polypeptide chain.

peptide bond

The covalent bond formed between the carboxyl end of one amino acid and the amino end of another during protein synthesis.

phenotypes

The observable physical or biochemical characteristics of an organism, as determined by both genetic makeup (genotype) and environment.

polypeptide 

A chain of amino acids connected by peptide bonds; once folded and processed, it may form a functional protein.

primase

An enzyme that synthesizes a short RNA primer during DNA replication, providing a starting point for DNA polymerase.

promotor 

A specific DNA sequence upstream of a gene where RNA polymerase binds to initiate transcription.

purine 

A class of nitrogenous bases (adenine and guanine) that have a double-ring structure.

pyrimidine 

A class of nitrogenous bases (cytosine, thymine in DNA; uracil in RNA) that have a single-ring structure.

regulator 

In gene expression, a molecule (such as a regulatory protein) that modulates transcription, translation, or other gene-expression steps.

ribosomes

Cellular organelles composed of ribosomal RNA and proteins; they are the site of protein synthesis (translation).

RNA polymerase

The enzyme that synthesizes RNA from a DNA template during transcription.

RNA primer

A short RNA sequence synthesized by primase during DNA replication; DNA polymerase uses it as a starting point.

silent mutation

A change in a DNA sequence that does not alter the amino acid sequence of the protein due to the redundancy of the genetic code.

snRNA

Small nuclear RNA; a class of RNA molecules involved in the processing (splicing) of pre-mRNA in the nucleus.

snRNPs

Small nuclear ribonucleoproteins; complexes of snRNA and proteins that form part of the spliceosome and remove introns from pre-mRNA.

spindle apparatus

The whole assembly of microtubules (spindle fibers) and associated proteins formed during cell division to segregate chromosomes.

spindle fibers

The individual microtubules that extend from centrosomes (or spindle poles) to chromosomes or other parts of the cell during mitosis or meiosis.

spliceosome

A large complex composed of snRNPs and other proteins that removes introns and joins exons in eukaryotic pre-mRNA.

sugar-phosphate backbone 

The alternating chain of sugar and phosphate groups that forms the structural framework of a DNA or RNA strand.

telomerase

An enzyme that adds repetitive nucleotide sequences to the ends (telomeres) of linear chromosomes, helping prevent shortening during replication.

topoisomerase

An enzyme that relieves the “twisting” tension in DNA (supercoils) ahead of replication forks or transcription by cutting and rejoining DNA strands.

transposons 

DNA sequences that can move (transpose) from one location in the genome to another; often called “jumping genes.”