DNA Structure, Function, and Gene Expression: Key Concepts for Biology

Johannes Miescher

First described DNA but did not know its function.

Frederick Griffith

Studied pneumonia-causing bacteria and discovered a transforming substance that changed harmless bacteria into lethal ones.

Avery and McCarty

Showed that DNA was the transforming principle.

Hereditary Material

A molecule must transmit a full complement of hereditary information, be found in the same amounts in cells of a given species, be exempt from major change, and be capable of encoding a huge amount of information.

Hershey and Chase

Confirmed in 1940 that DNA meets the criteria for hereditary material through bacteriophage experiments.

Somatic Cell Nuclear Transfer

A method used to produce clones.

DNA Molecule Structure

Consists of two strands of nucleotide monomers running in opposite directions and coiled into a double helix.

DNA Nucleotide Composition

Contains one five-carbon sugar (deoxyribose), three phosphate groups, and one nitrogen-containing base (adenine, thymine, guanine, or cytosine).

Adenine (A)

One of the four DNA nucleotides.

Guanine (G)

One of the four DNA nucleotides.

Cytosine (C)

One of the four DNA nucleotides.

Thymine (T)

One of the four DNA nucleotides.

Chargaff's Rules

Bases of the two DNA strands in a double helix pair in a consistent way: A-T and C-G.

Watson and Crick

Shared ideas about the structure of DNA and built models from scraps of metal.

Franklin and Wilkins

Worked on identical samples of DNA and contributed to the understanding of DNA structure.

Erwin Chargaff

Discovered the relationships between DNA bases.

Rosalind Franklin

Discovered the structure of DNA by X-ray crystallography.

Maurice Wilkins

Provided experimental evidence of DNA structure.

James Watson and Francis Crick

Built the first accurate model of a DNA molecule.

Franklin's Data

Provided critical data about DNA's structure, including phosphate backbones on the outside of the double helix.

The Double Helix

Proposed by Watson and Crick as consisting of two strands of nucleotides, running in opposite directions, coiled into a double helix held together by hydrogen bonds.

DNA Sequence

The order of nucleotide bases in a DNA strand (DNA sequence) is genetic information.

Complementary Base Pairs

The two strands of a DNA molecule are complementary.

Chromosome

Condensed structure of DNA inside cell.

Histone

"Spools" of proteins that the DNA strand wraps around inside chromosome.

Chromosome Number

Sum of all chromosomes in a cell of a given type.

Diploid

Cells having two of each type of chromosome characteristic of the species (2n).

Karyotype

Image of an individual's complement of chromosomes arranged by size, length, shape, and centromere location.

Sister chromatid

One of two attached members of a duplicated eukaryotic chromosome.

Centromere

Constricted region in a eukaryotic chromosome where sister chromatids are attached.

Autosomes

Paired chromosomes with the same length, shape, centromere location, and genes.

Sex chromosomes

Members of a pair of chromosomes that differ between males and females.

DNA replication

It is a process by which a cell copies its DNA before it divides.

Semiconservative replication

One strand of each molecule is parental (old) and the other is new.

DNA polymerase

DNA replication enzyme; assembles a new strand of DNA based on sequence of a DNA template.

Primer

Short, single strand of DNA that base-pairs with a targeted DNA sequence.

DNA ligase

Enzyme that seals breaks in double-stranded DNA.

Mutation

A permanent change in DNA sequence.

Replication Error

Uncorrected errors in DNA replication may become mutations.

Ionizing radiation

Can knock electrons out of atoms, breaking DNA.

Nonionizing radiation

Forms nucleotide dimers that kink DNA and increase mutation rate.

Chemicals in tobacco smoke

Transfer methyl groups (CH3) to nucleotide bases in DNA, causing mispairs during replication.

Environmental pollutants

Breakdown products bind irreversibly to DNA, causing replication errors.

Gene

DNA sequence that encodes an RNA or protein product with a sequence of nucleotide bases (A, T, G, C)

Transcription

Process of enzymes using the gene's DNA sequence as a template to assemble a strand of messenger RNA (mRNA)

Translation

mRNA decoded in a sequence of amino acids; result is a polypeptide chain that folds into a protein

Gene Expression

Process by which the information in a gene becomes converted to an RNA or protein product

RNA Polymerase

The enzyme that adds nucleotides to the end of a growing RNA strand during transcription

Promoter Sequence

A sequence near the beginning of a gene where RNA polymerase binds to initiate transcription

Exons

Sequences that stay in the RNA after processing in eukaryotic cells

Introns

Sequences removed during RNA processing in eukaryotic cells

Poly-A Tail

A tail of 50 to 300 adenines added to the end of a new mRNA after splicing

Codons

Sets of three nucleotides in mRNA that form 'words' in the genetic code

Genetic Code

A system where sixty-four codons encode twenty amino acids, with some amino acids specified by more than one codon

tRNA

Transfer RNA that delivers amino acids to the ribosome during translation

rRNA

Ribosomal RNA that joins with proteins to form intact ribosomes

mRNA

Messenger RNA that carries the information from DNA to the ribosome for protein synthesis

Stop Codon

A codon that signals the end of translation

Amino Acids

Building blocks of proteins specified by codons in mRNA

Polypeptide Chain

A chain of amino acids that folds into a protein

Base Pairing Rules

Rules that dictate how nucleotides pair with each other during DNA replication and RNA synthesis

RNA Modifications

Changes made to RNA in eukaryotic cells before it leaves the nucleus

Cytoplasm

The part of the cell where translation occurs

Initiator tRNA

The tRNA that base-pairs with the first mRNA codon during translation initiation

Ribosome

A cellular structure that assembles polypeptide chains during translation

Base-pair substitution

Type of mutation in which a single base-pair changes.

Sickle-cell anemia

An example of a mutation that results from base-pair substitution.

Reading frame shift mutations

Mutations that shift the reading frame of the mRNA codons.

Deletion

The removal of one or more base pairs in a mutation.

Insertion

The addition of one or more base pairs in a mutation.

Beta thalassemia

An example of a mutation that results from reading frame shift mutations.

Differentiation

The process by which cells become specialized.

Transcription factor

Protein that influences transcription by binding to DNA.

Master gene

Gene encoding a product that affects the expression of many other genes.

Homeotic gene

Type of master gene that controls formation of specific body parts during development.

Gene knockout

Altering the expression of a homeotic gene by deleting it entirely.

PAX6 gene

In humans and many other animals, the PAX6 gene affects eye formation.

X chromosome inactivation

The process that equalizes expression of X chromosome genes between the sexes.

SRY gene

Master gene for male sex determination that triggers formation of testes.

Lactose tolerance

The ability to digest lactose, which most species lose after a certain age.

Lactase gene

Gene that is no longer transcribed after age five in most humans.

DNA methylation

Modifications that suppress gene expression by adding a methyl group to DNA nucleotides.

Epigenetics

Heritable changes in gene expression that are not due to changes in underlying DNA sequence.

Methyl group

A chemical group (CH3) that can be added to histone proteins or DNA nucleotides to affect transcription.

Bacterial breakdown of lactose

Occurs when lactose passes undigested through the small intestine, leading to gas production.

Dosage compensation

Theory that explains how X chromosome inactivation equalizes gene expression between sexes.