UGA Biology 1107 Spring Unit 2 Study Guide

Mutation

change in a DNA sequence that affects genetic information. This occurs when the enzyme responsible for replication (DNA polymerase) makes an error and inserts the wrong nucleotide. DNA polymerase itself and other enzymes usually catch these mistakes and fix them

Mutagens

are chemicals or radiation that react with and alter DNA, such as arsenic, asbestos, and ultraviolet radiation. These changes make the molecule difficult for DNA polymerase to accurately read, and although many of the extra mistakes are caught and fixed by repair enzymes, some will slip through and increase the overall number of mutations in the cell

Point Mutations

are mutations that alter a single nucleotide pair in the DNA

Silent Mutations

will change a DNA sequence but do not impact the resulting protein, because the original and new codon represent the same amino acid

Missense Mutation

changes a codon such that a different amino acid is placed during translation

Frameshift mutation

occurs when nucleotides are added (insertion) or removed (deletion) from a DNA sequence, causing the reading frame for the gene to shift

Chromatin

DNA molecules are wrapped around proteins called histones to form a DNA-protein complex

Chromosome

A single molecule of DNA and the proteins it is wrapped around

Chromatid

one of two identical "sister" parts of a duplicated chromosome

Centromere

Region of a chromosome where the two sister chromatids attach

Zygote

fertilized egg; single cell

Conservative Replication

the two DNA strands in the original DNA molecule (parental DNA) remain together and make up one of the two copies that result from replication. Two new DNA strands (daughter strands) join together to form the other copy

Semiconservative Replication

each DNA molecule produced consists of one parental and one daughter strand

Dispersive Replication

both strands of both DNA molecules resulting from replication would have sections of original and new DNA that are mixed together

Isotopes

Atoms of the same element that have different numbers of neutrons

Topoisomerase

is an enzyme that prevents the twisting from forming into a knot and halting replication. This enzyme temporarily cuts the sugar-phosphate backboneof DNA to relieve the twisting and then repairs the cut

Helicase

enzymes recognize and bind to DNA sequences at the origins of replication and break the hydrogen bonds between nitrogenous bases that hold the two strands together

Single-Strand Binding Proteins (SSBPs)

keep the separated DNA strands apart, preventing them from reforming hydrogen bonds. This allows other enzymes to attach to the DNA strands to carry out replication.

Primase

is an enzyme that uses the template DNA to produce short stretches of complementary RNA

Primers

short segments of DNA that guide DNA polymerase to the section of DNA to copy

DNA Polymerase

Enzyme involved in DNA replication that joins individual nucleotides to produce a DNA molecule

DNA Ligase

A linking enzyme essential for DNA replication; catalyzes the covalent bonding of the 3' end of a new DNA fragment to the 5' end of a growing chain.

Replication Fork

A Y-shaped region on a replicating DNA molecule where new strands are growing.

Leading Strand

is built continuously in the 5' to 3' direction toward the replication fork by using the 3' to 5' strand as a template.

Lagging Strand

replication of that strand must be restarted again and again as helicase continuously unwinds the DNA. This results in the new strand

Okazaki Fragments

Small fragments of DNA produced on the lagging strand during DNA replication, joined later by DNA ligase to form a complete strand.

Telomeres

Cells with linear chromosomes deal with this problem by having specialized DNA sequences at the ends of the chromosomes. Telomeres are composed of a repetitive sequence of nucleotides that does not code for information needed by cells.

Telomerase

These cells are able to avoid chromosome shortening during DNA replication with the help of an enzyme

Polymerase Chain Reaction (PCR)

is a laboratory method that is used to make millions or billions of copies of a DNA segment that is of interest to researchers, such as a gene or a region used by forensic specialists to match tissues with individuals

Amplification

PCR only copies a small portion of the DNA present in a cell. Also, rather than making just one copy, the steps of PCR are repeated multiple times to produce many copies of a specific DNA region in a process

Taq Polymerase

is a type of DNA polymerase that is named after the heat-tolerant bacteria from which it was isolated (Thermus aquaticus). These bacteria live in hot springs and have enzymes that evolved to function at high temperatures. Taq polymerase can withstand temperatures close to boiling and is most active at 72°C, which is far too hot for other DNA polymerases. This heat stability makes Taq polymerase ideal due to the high temperatures involved in PCR

Denaturation (94-96°C)

Heat is applied to separate (denature) the DNA strands, which provides single-stranded templates for the next step.

Annealing (50-65°C)

Cool ingredients such that the primers can bind (anneal) to their complementary sequences on the single-stranded template DNA.

Extension (72°C)

Raise to optimal temperature for Taq polymerase to replicate DNA.