A&P Chapter 4

Nucleic acid

A polymer made of nucleotide monomers.

Nucleotide

The monomer of DNA and RNA; consists of a sugar, a phosphate group, and a nitrogenous base.

Nitrogenous base

A single- or double-ringed component of a nucleotide that varies among nucleotides.

Purine

A nitrogenous base with two carbon-nitrogen rings; adenine and guanine are purines.

Pyrimidine

A nitrogenous base with one carbon-nitrogen ring; cytosine and thymine are pyrimidines.

Adenine (A)

A purine nitrogenous base found in DNA and RNA.

Guanine (G)

A purine nitrogenous base found in DNA and RNA.

Cytosine (C)

A pyrimidine nitrogenous base found in DNA and RNA.

Thymine (T)

A pyrimidine nitrogenous base found in DNA but not RNA.

DNA (deoxyribonucleic acid)

A long nucleic acid molecule that carries the genes and provides instructions for protein synthesis.

Double helix

The spiral-staircase structure of DNA formed by two sugar-phosphate backbones held together by paired nitrogenous bases.

Sugar-phosphate backbone

The sides of the DNA double helix, composed of alternating phosphate groups and deoxyribose sugars.

Base pair

A pair of complementary nitrogenous bases joined by hydrogen bonds across the two DNA strands; A pairs with T and C pairs with G.

Hydrogen bond

A bond that holds complementary nitrogenous bases together between the two DNA strands.

Complementary base pairing

The rule that adenine pairs with thymine and cytosine pairs with guanine, so the sequence of one DNA strand determines the sequence of the other.

A–T base pair

A DNA base pair consisting of adenine and thymine, held together by two hydrogen bonds.

C–G base pair

A DNA base pair consisting of cytosine and guanine, held together by three hydrogen bonds.

Gene

An information-containing segment of DNA that codes for production of an RNA molecule, which in most cases plays a role in synthesizing one or more proteins.

Protein-coding gene

A gene whose RNA product ultimately directs the synthesis of a protein.

Noncoding DNA

DNA that does not code for proteins but can have roles in chromosome structure and regulation of gene activity.

Chromatin

A fine filamentous material consisting of DNA complexed with proteins.

Chromosome

A long filament of chromatin containing DNA and proteins; most human cells have 46 chromosomes.

Histone

A protein around which DNA winds during the packaging of chromatin.

Chromosome territory

A spheroidal region of the nucleus occupied by a chromosome and permeated by channels that allow regulatory chemicals access to genes.

Sister chromatids

The two genetically identical copies of a chromosome produced when its DNA is replicated.

Centromere

The pinched region where sister chromatids are joined together.

Kinetochore

A protein plaque on each side of a chromosome's centromere that plays a role in cell division.

RNA (ribonucleic acid)

A nucleic acid generally consisting of a single nucleotide chain that uses ribose and contains uracil instead of thymine.

Ribose

The sugar found in RNA nucleotides.

Uracil (U)

The nitrogenous base found in RNA in place of thymine.

Messenger RNA (mRNA)

RNA that carries genetic instructions from DNA to the cytoplasm and serves as a code for assembling a protein.

Transfer RNA (tRNA)

A relatively small RNA that binds a free amino acid and delivers it to the ribosome during protein synthesis.

Ribosomal RNA (rRNA)

RNA that is a component of ribosomes and participates in protein synthesis.

Noncoding RNA (ncRNA)

RNA that does not direct protein synthesis and can have regulatory or enzymatic roles.

DNA sugar

Deoxyribose.

RNA sugar

Ribose.

DNA nitrogenous bases

A, T, C, and G.

RNA nitrogenous bases

A, U, C, and G.

DNA strand structure

Two nucleotide chains arranged as a double helix.

RNA strand structure

One nucleotide chain, although it can fold back on itself in certain regions.

DNA location of action

Functions in the nucleus and does not leave it.

RNA location of action

Leaves the nucleus and functions mainly in the cytoplasm.

DNA function

Codes for synthesis of RNA and proteins.

RNA function

Carries out the instructions in DNA and participates in protein assembly.

Genome

All the DNA, both coding and noncoding, in one 23-chromosome set.

Genomics

The comprehensive study of the genome and how its genes and noncoding DNA affect the structure and function of an organism.

Genomic medicine

The application of knowledge of the genome to the prediction, diagnosis, and treatment of disease.

Single-nucleotide polymorphism (SNP)

A variation involving a single nucleotide that contributes to human genetic variation.

Proteome

The collection of all the different proteins that can be produced by the body.

Genetic code

The system that enables the four DNA nucleotides to specify the amino acid sequences of proteins.

Base triplet

A sequence of three DNA nucleotides that represents one amino acid.

Codon

A three-base sequence in mRNA that represents an amino acid or a stop signal.

Stop codon

A codon that signals the end of the instructions for a protein; UAG, UGA, and UAA are stop codons.

Start codon

The codon AUG, which signals the beginning of protein synthesis and codes for methionine.

AUG

A start codon in mRNA that also codes for the amino acid methionine.

Protein synthesis

The process by which genetic instructions in DNA are used to produce proteins through transcription and translation.

Transcription

The process of copying genetic instructions from DNA into RNA.

RNA polymerase

An enzyme that binds to DNA, reads one DNA strand, and assembles a complementary RNA molecule during transcription.

Pre-mRNA

The initial, immature RNA molecule produced by transcription that contains both exons and introns.

Exon

A segment of pre-mRNA that remains in the mature mRNA and can be translated into a protein.

Intron

A segment of pre-mRNA that is removed before translation.

Splicing

The process of removing introns and joining exons together to produce functional mRNA.

Alternative splicing

A process in which different combinations of exons from one pre-mRNA are joined together, allowing one gene to produce more than one protein.

Translation

The process of converting the language of nucleotides into the language of amino acids to produce a protein.

mRNA

The RNA molecule that carries the genetic code from the nucleus to the cytoplasm and provides the instructions for protein synthesis.

mRNA protein cap

A protein structure acquired by mRNA during its synthesis that allows it to pass through a nuclear pore and helps a ribosome recognize where to begin translation.

tRNA

A small RNA molecule that binds a free amino acid and delivers it to the ribosome for addition to a growing protein chain.

Anticodon

A three-base sequence on tRNA that pairs with a complementary codon on mRNA.

Ribosome

A cellular structure that reads mRNA and facilitates the joining of amino acids into a protein.

Peptide bond

The bond formed between amino acids as they are joined into a growing protein chain.

Initiation

The first stage of translation, in which the ribosome recognizes the start codon AUG and an initiator tRNA carrying methionine binds to it.

Elongation

The stage of translation in which successive tRNAs pair their anticodons with mRNA codons and the ribosome joins the amino acids into a growing protein chain.

Termination

The final stage of translation, in which the ribosome reaches a stop codon and the completed protein is released.

Initiator tRNA

A tRNA carrying methionine that recognizes the AUG start codon at the beginning of translation.

Posttranslational modification

Changes made to a newly synthesized protein after or during its assembly, including removing amino acid segments, folding the protein, forming disulfide bridges, and adding carbohydrates.

Rough endoplasmic reticulum (rough ER)

The organelle where proteins destined for certain cellular locations or secretion are assembled and processed.

Transport vesicle

A membrane-bound vesicle that carries newly synthesized proteins from the rough ER to the Golgi complex.

Clathrin

A protein coating that helps select proteins for transport vesicles and helps shape the vesicles as they form.

Golgi complex

An organelle that modifies, sorts, and packages proteins received from the rough ER.

Cis Golgi cistern

The Golgi cistern closest to the rough ER that receives cargo arriving from the ER.

Trans Golgi cistern

The Golgi cistern farthest from the ER that produces Golgi vesicles containing processed cell products.

Secretory vesicle

A vesicle that carries a cell product to the plasma membrane for release by exocytosis.

Exocytosis

The process by which a secretory vesicle fuses with the plasma membrane and releases its contents outside the cell.

Gene regulation

The control of when and how much a gene is expressed.

Gene expression

The process by which a gene is turned on and produces a detectable effect in the individual.

Regulatory protein

A protein that regulates gene activity, including proteins that can activate transcription.

Transcription activator

A regulatory protein that promotes transcription of a gene.

Gene silencing

The prevention of gene expression by making a gene less accessible for transcription.

Hormonal gene activation

Activation of a gene in response to a hormonal signal, in which intracellular signaling ultimately activates regulatory proteins that promote transcription.

DNA replication → The process of copying DNA before cell division so that each daughter cell receives a complete and identical copy of the genes.

Replication fork → The point where DNA is opened up as the double helix separates during DNA replication.

DNA helicase → An enzyme that opens the DNA double helix by separating its two strands, exposing their nitrogenous bases.

DNA polymerase → An enzyme that reads the exposed bases of a DNA strand and assembles complementary free nucleotides to make a new DNA strand.

DNA ligase → An enzyme that joins the short DNA segments produced on one strand into a continuous DNA strand.

Semiconservative replication → DNA replication in which each daughter DNA molecule contains one strand from the original parental DNA molecule and one newly synthesized strand.