Biology 30 - Chapter 18

deoxyribonucleic acid (DNA)

a double-stranded nucleic acid molecule that governs the processes of heredity in the cells of organisms; composed of nucleotides containing a phosphate group, a nitrogenous base (adenine, guanine, cytosine, or thymine), and deoxyribose

ribonucleic acid (RNA)

a nucleic acid molecule that plays a role in gene expression and protein synthesis, composed of a phosphate group, a nitrogenous base (adenine, guanine, cytosine, or uracil), and the five-carbon sugar ribose; structure is similar to DNA

transforming principle

ability of dead pathogenic bacteria to pass on their disease-causing properties to live, non-pathogenic bacteria; phenomenon described by Frederick Griffith in 1928

Nucleotides

units making up nucleic acids (e.g., DNA, RNA), composed of a five-carbon sugar, a phosphate group, and one of five nitrogen-containing bases (adenine, cytosine, guanine, and either thymine or uracil)

Chargaff’s rule

in any sample of DNA, a constant relationship in which the amount of adenine is always approximately equal to the amount of thymine, and the amount of cytosine is always approximately equal to the amount of guanine

complementary base pairs

refers to the hydrogen-bonded, nitrogenous base pairs of adenosine and thymine, and of cytosine and guanine in the DNA double helix, or to the base pairs of adenosine and uracil, and of cytosine and guanine in hybrid molecules that link complementary strands of RNA and DNA

Antiparallel

describes the property by which the 5’ to 3’ phosphate bridges run in opposite directions on each strand of nucleotides in a double-stranded DNA molecule

Gene

the basic unit of heredity; a specific sequence of DNA that encodes a protein, tRNA, rRNA molecule, or regulates the transcription of such a sequence; governs the expression of a particular trait and can be passed to an offspring

Genome

the sum of all the DNA carried in an organism’s cells

Replication

in genetics, process of creating an exact copy of a molecule of DNA

Semi-conservative

term used to describe replication

replication origin

specific nucleotide sequence where replication begins; ranges from a single replication origin in prokaryotes to thousands in eukaryotes

Helicase

set of enzymes that cleave and unravel short segments of DNA just ahead of the replicating fork during DNA replication

replication bubble

oval-shaped unwound area within a DNA molecule that is being replicated

replication fork

during DNA replication, Y-shaped points at which the DNA helix is unwound and new strands develop

DNA polymerase

during DNA replication, an enzyme that slips into the space between two strands, uses the parent strands as a template, and adds nucleotides to make complementary strands

Elongation

the process of joining nucleotides to extend a new strand of DNA; relies on the action of DNA polymerase

Primer

in DNA replication, short strand of RNA that is complementary to a DNA template and serves as a starting point for the attachment of new nucleotides

leading strand

in DNA replication, the strand that is replicated continuously

lagging strand

in DNA replication, the strand that is replicated in short segments rather than continuously

Okazaki fragments

short nucleotide fragments synthesized during DNA replication of the lagging strand

DNA ligase

enzyme that splices together Okazaki fragments during DNA replication on the lagging strand or sticky ends that have been cut by a restriction endonuclease; catalyzes the formation of phosphate bonds between nucleotides

Primase

in DNA replication, enzyme that forms a primer used as a starting point for the attachment of new nucleotides

replication machine

complex involving dozens of different enzymes and other proteins that work closely together in the process of DNA replication and interact at the replication fork

Termination

in DNA replication, the completion of the new DNA strands and the dismantling of the replication machine

DNA sequencing

the process of identifying the precise nucleotide sequence of a DNA fragment

Human Genome Project

joint effort of thousands of researchers from laboratories worldwide that determined the sequence of the three billion base pairs making up the human genome

amino acids

an organic compound consisting of a carboxylic acid group (COOH), an amino group (NH2), and any of various side groups, linked together by peptide bonds to form proteins

genetic code

the order of base pairs in a DNA molecule

gene expression

the transfer of genetic information from DNA to RNA to protein

Transcription

the first stage of gene expression, in which a strand of messenger RNA (mRNA) is produced that is complementary to a segment of DNA

messenger RNA (mRNA)

strand of RNA that carries genetic information from DNA to the protein synthesis machinery of the cell during transcription

transfer RNA (tRNA)

type of RNA that works with messenger RNA (mRNA) to direct the synthesis of a polypeptide in a process known as translation

Translation

the second stage of gene expression, in which the mRNA nucleotide sequence directs the synthesis of a polypeptide (a chain of amino acids) with the aid of another RNA molecule, transfer RNA (tRNA)

Codon

in a gene, each set of three bases (for example, ACC or GAA) that code for an amino acid or a termination signal

RNA polymerase

main enzyme that catalyzes the formation of RNA from the DNA template

Promoter

during transcription, a sequence of nucleotides on the DNA molecule that tells the RNA polymerase complex where to bind

Anticodon

specialized base triplet located on one lobe of a transfer RNA (tRNA) molecule that recognizes its complementary codon on a messenger RNA (mRNA) molecule

ribosomal RNA (rRNA)

linear strand of RNA that remains associated with the ribosomes

Genomics

the study of genomes as opposed to individual genes

Proteomics

the study of all proteins that are produced by a given genome

Mutation

a permanent change in a cell’s DNA; includes changes in nucleotide sequence, alteration of gene position, gene loss, or duplication and insertion of foreign sequences; an inheritable mutation has the potential to affect an entire gene pool

somatic cell mutation

permanent change in the genetic material of a body cell, not including germ cells, during the lifetime of an organism; is copied during DNA replication and passed on to daughter cells, but not passed on to future generations; compare germ line mutation

germ line mutation

permanent change in the genetic material of a reproductive cell during the lifetime of an organism that is passed on to future generations; compare somatic cell mutation

point mutation

permanent change in the genetic material of a cell that affects one or just a few nucleotides; may involve the substitution of one nucleotide for another, or the insertion or deletion of one or more nucleotides

silent mutation

permanent change in the genetic material of a cell that has no effect on the function of the cell

mis-sense mutation

permanent change in the genetic material of a cell that results in a slightly altered but still functional protein

nonsense mutation

permanent change in the genetic material of a cell that renders a gene unable to code for a functional protein

frameshift mutation

permanent change in the genetic material of a cell caused by the insertion or deletion of one or two nucleotides so that the entire reading frame of the gene is altered; usually results in a nonsense mutation

Mutagen

substance or event that increases the rate of mutation in an organism; may be physical or chemical

physical mutagen

agent that can forcibly break a nucleotide sequence, causing random changes in one or both strands of a DNA molecule; (e.g., X rays)

chemical mutagen

molecule that can enter the cell nucleus and induce a permanent change in the genetic material of the cell by reacting chemically with DNA; e.g., nitrites

Carcinogenic

cancer-causing; describes a factor, such as a chemical mutagen, that is associated with one or more forms of cancer

mitochondrial DNA (mtDNA)

DNA within the mitochondria; is genetically identical to that of the female parent because the cytoplasm of offspring is derived from the egg (ovum)

genetic engineering

manipulation of genetic material to alter genes and blend plant, animal, and bacterial DNA

recombinant DNA

a molecule of DNA that includes genetic material from different sources

restriction enzyme

enzyme in prokaryotes that catalyzes the cleavage of DNA at specific nucleotide sequences

restriction endonuclease

type of restriction enzyme that recognizes a specific short sequence of nucleotides within, rather than at the ends of, a strand of DNA and cuts the strand at that particular point within the sequence

restriction fragment

small segments of DNA cut from a DNA molecule by a restriction endonuclease

gel electrophoresis

tool used to separate molecules according to their mass and charge; can be used to separate fragments of DNA

DNA fingerprint

the pattern of bands into which DNA fragments sort during gel electrophoresis

Biotechnology

the use of natural biological systems to create useful new technologies and products

DNA microarray

a chip (usually a glass microscope slide or polymer membrane) that contains a grid of thousands of microscopic cells; each cell contains a nucleic acid sequence that can bind with one of the mRNA molecules transcribed during gene expression; allows scientists to analyze the activity of thousands of genes at once

copy DNA (cDNA)

artificial form of DNA synthesized from the mRNA of cell samples during a DNA microarray experiment

Transgenic

genetically engineered; organism is produced by incorporating the DNA from one organism into another to create a new genetic combination

Bioremediation

use of living cells to perform environmental clean-up tasks, such as using bacteria to degrade PCBs into harmless compounds

Clone

one of a pair of organisms (or more) that are genetically identical

Ultrasound

sound with a frequency greater than the upper limit of human hearing; used in a procedure by which sound waves sent through the body provide information about internal structures, such as a developing fetus

Amniocentesis

procedure by which a needle is used to withdraw a small sample of amniotic fluid from the uterus in order to perform a genetic analysis; for safety, cannot be performed before the 14th week of pregnancy

chorionic villi sampling

procedure where fetal cells are removed from the chorion (a tissue that surrounds the amniotic sac and makes up the fetal placenta) to perform a genetic analysis; can be performed around the 9th week of pregnancy

genetic marker

a characteristic that provides information about the genotype of an individual (18.4)genetic screening any of several methods of identifying people who are at risk of developing particular genetic conditions or of passing these conditions on to their children

DNA probe

molecule of DNA with a nucleic acid sequence that is labelled with a radioactive or fluorescent chemical tag; binds to a complementary DNA sequence and can be used to locate a specific genetic marker

gene therapy

the process of changing the function of genes to treat or prevent genetic disorders

DNA vector

in gene therapy, something (commonly, a modified form of virus) that carries recombinant DNA containing a desired gene into a host cell in order to incorporate the gene into a patient’s genome

somatic gene therapy

therapy that is aimed at correcting genetic disorders in somatic (body) cells

germ-line therapy

gene therapy used to modify the genetic information carried in egg and sperm cells; see also gene therapy