DNA and RNA Structures, DNA Replication

Phenotype

Observable traits or characteristics of an organism

Genotype

Genetic makeup of an organism (DNA sequence)

DNA blueprint concept

DNA contains instructions for building proteins and determining traits

Chromosomal theory of inheritance

Chromosomes carry genetic information

Transformation

Process where cells take up external DNA from their environment

Griffith’s experiment

Showed that a “transformation factor” could transfer disease-causing traits

Avery, MacLeod, McCarty experiment

Proved DNA is the hereditary material (not protein or RNA)

DNA as genetic material

DNA is responsible for storing and transmitting genetic information

Chromatin

DNA wrapped around histone proteins forming chromosomes

Nucleosome

Basic unit of chromatin (DNA wrapped around histone octamer)

Histone proteins

Proteins that help package DNA into chromatin

Euchromatin

Loosely packed chromatin; transcriptionally active (genes ON)

Heterochromatin

Tightly packed chromatin; transcriptionally inactive (genes OFF)

Nucleic acids

Biomolecules that include DNA and RNA

Nucleotide

Building block of nucleic acids (phosphate + sugar + base)

Phosphate group

Component of nucleotide linking sugars together

Pentose sugar

Deoxyribose (DNA) or ribose (RNA)

Nitrogenous bases

A, G, C, T (DNA) and A, G, C, U (RNA)

Purines

Adenine (A) and guanine (G) (double-ring structures)

Pyrimidines

Cytosine (C), thymine (T), uracil (U) (single-ring structures)

DNA bases

A, T, G, C

RNA bases

A, U, G, C

Phosphodiester bond

Bond linking nucleotides in a DNA/RNA strand

DNA structure

Double helix with two antiparallel strands

Antiparallel strands

One strand runs 5’→3’, the other 3’→5’

Base pairing rules

A pairs with T (2 H-bonds), G pairs with C (3 H-bonds)

Watson and Crick

Proposed double helix structure of DNA

Rosalind Franklin

Provided X-ray diffraction data for DNA structure

RNA

Single-stranded molecule involved in protein synthesis

mRNA

Messenger RNA carries genetic info from DNA to ribosome

Transcription

Process of copying DNA into mRNA

Translation

Process of building proteins using mRNA at ribosome

Gene

Sequence of DNA that codes for a functional product (protein or RNA)

Mutation

Change in DNA nucleotide sequence

DNA replication

Copying of DNA before cell division

Semi-conservative replication

Each new DNA molecule has one old strand and one new strand

Template strand

Original DNA strand used to build a new complementary strand

DNA polymerase

Enzyme that synthesizes new DNA strand

Complementary base pairing in replication

A-T and G-C pairing ensures accuracy

Chromatids

Identical DNA molecules formed after replication

Centromere

Region joining sister chromatids

Replication errors

Mistakes in DNA copying that may lead to mutations

DNA repair mechanisms

Systems that correct replication errors

UV damage to DNA

Causes mutations if not repaired

Xeroderma pigmentosum (XP)

Genetic disorder with defective DNA repair and UV sensitivity