DNA and Its Role in Heredity Vocabulary

Flashcards for reviewing key vocabulary from Chapter 9: DNA and Its Role in Heredity.

Chromosome Theory of Inheritance

The theory that heritable information is carried by molecules, eventually found to be DNA.

Location of DNA

DNA is present in the cell nucleus and in chromosomes.

DNA during S phase

DNA doubles during the S phase of the cell cycle.

DNA in Diploid vs. Haploid Cells

There is twice as much DNA in diploid cells as in haploid cells.

Transformation Experiment

Demonstrated that DNA from one strain of bacterium could genetically transform another strain.

Bacteriophage Experiment

Showed that when a virus infects a bacterium, it injects only its DNA, not protein.

Polymer

DNA was known to be a polymer of nucleotide monomers by the mid-20th century.

Deoxyribose

The sugar component of a nucleotide.

Phosphate Group

A component of a nucleotide.

Nitrogen-Containing Bases

Adenine (A), Guanine (G), Cytosine (C), and Thymine (T).

Purines

Adenine (A) and Guanine (G)

Pyrimidines

Cytosine (C) and Thymine (T)

Chargaff's Rule

The amount of A always equals the amount of T, and the amount of G always equals the amount of C.

X-ray Crystallography

Positions of atoms in a crystallized substance can be inferred from the diffraction pattern of X-rays.

Rosalind Franklin

Prepared crystallographs of DNA suggesting a spiral or helical molecule.

Watson and Crick

Combined all the knowledge of DNA to determine its structure in 1953.

Antiparallel Strands

DNA strands must run in opposite directions, 5' to 3'.

Complementary Base Pairing

Explains Chargaff's rules and the constant thickness of the DNA molecule.

Van der Waals Interactions

Weak interactions that cause adjacent bases to stack like poker chips.

Major and Minor Grooves

Result from sugar-phosphate backbones being closer together on one side of the double helix.

Protein-DNA Interactions

Binding of proteins to specific base-pair sequences.

DNA as a Template

Each strand can act as a template to make a new strand because of complementary base pairing.

Semiconservative Replication

Each parental strand is a template for a new strand.

Conservative Replication

The two parental strands remain together in one daughter molecule.

Dispersive Replication

Parent molecule is dispersed among both strands in the two daughter molecules.

Density Isotope

15N is a heavy isotope that makes DNA more dense, was used in Meselson-Stahl experiment.

Meselson-Stahl Experiment

Showed that DNA replication is semiconservative.

Initiation (DNA Replication)

Unwinding the DNA double helix and synthesizing RNA primers.

Elongation (DNA Replication)

Synthesizing new strands of DNA using each of the parental strands as templates.

Termination (DNA Replication)

When synthesis ends.

Direction of DNA Synthesis

Always proceeds in the 5ʹ-to-3ʹ direction.

Template Strand Direction

Always read in the 3ʹ-to-5ʹ direction.

DNA Helicase

Catalyzes the separation of the two strands of DNA at each fork.

Primer

A short RNA strand synthesized by primase.

Primase

Synthesises a short RNA strand, the primer.

DNA Polymerases

Require a primer to start polymerization.

RNA Polymerases

Do not require primers.

Leading Strand

DNA is synthesized continuously in the same direction as fork movement.

Lagging Strand

Synthesis is in the opposite direction to fork movement and requires constant repriming.

Okazaki Fragments

Series of fragments created during lagging strand synthesis.

DNA Ligase

Catalyzes the final phosphodiester linkage between Okazaki fragments.

End-Replication Problem

When the last primer is removed from the lagging strand, a single-strand bit of DNA is left at each end.

Telomeres

Repetitive sequences at the ends of eukaryotic chromosomes.

Telomerase

Enzyme that can add telomeres back on.

Apoptosis

Cell death.

Mutations

Permanent, inherited changes in DNA sequence.

Incorporation Error Rate

Probability that an incorrect base will be inserted is about 1 in 100,000.

Proofreading

DNA polymerase recognizes a mismatch, backs up, removes mismatched nucleotide, then recommences synthesis.

Mismatch Repair

After replication, a protein complex scans for mismatched bases and replaces the mismatched fragment.

Base-Pair Substitutions

A single base is changed, inserted, or deleted.

Point mutations

A single base is changed, inserted, or deleted.

Spontaneous Mutations

Caused by polymerase errors or spontaneous chemical changes in bases.

Tautomeric Shift

Bases have two isomers (tautomers). When a base temporarily forms its rare tautomer it can pair with a different base, leading to a mismatch.

Deamination

Loss of an NH2 group in cytosine, forming uracil.

Induced Mutations

Caused by mutagens.

Mutagens

Chemicals or radiation that can damage DNA.

Excision Repair

Removes damaged nucleotides and replaces them with normal ones.

Thymine Dimers

Covalent linkages between adjacent thymines formed on exposure to UV radiation.

Photolyase

Uses light energy to repair Thymine Dimers.

Somatic Mutations

Occur in somatic (body) cells and are not passed to offspring.

Germ Line Mutations

Occur in germ line cells (gametes) and are passed to offspring.

Silent Mutations

Do not affect protein function.

Loss of Function Mutations

Prevent gene transcription or produce nonfunctional proteins; nearly always recessive.

Gain of Function Mutations

Lead to a protein with altered function, usually dominant; common in cancer cells.

Conditional Mutations

Affect the phenotype only under certain environmental conditions.

Chromosomal Mutations

Extensive changes in genetic material involving long DNA sequences.

Deletions

Loss of a chromosome segment; can have severe or fatal consequences.

Duplications

A portion of a chromosome is replicated, resulting in multiple copies.

Overexpression

extra gene copies may lead to overexpression of genes

Inversions

Result from breaking and rejoining, but the segment is flipped.

Translocations

Segment of DNA breaks off and is inserted into another chromosome.

Chromosomal Rearrangements

Involve double-strand breaks.

Aberrant Crossover

An aberrant crossover between homologous or nonhomologous chromosomes can lead to chromosomal rearrangements.

Ionizing Radiation

One method used to kill tumor cells.

Pre-replication Complex

A large protein complex that binds to the origin of replication.

Origin of Replication (ori)

A specific site where the pre-replication complex binds.

Replication Forks

Move away from the origin of replication during synthesis of new DNA strands.

Single-Strand Binding Proteins

Proteins that prevent the separated DNA strands from re-annealing during replication.

DNA Sequencing

The process of determining the order of nucleotide bases in a DNA molecule. Polymerases allow the development of this and PCR.

Polymerase Chain Reaction (PCR)

A technique used to amplify specific DNA sequences. Polymerases allow the development of this and DNA sequencing.