Genetics chapter 10

X ray diffraction

X ray diffraction

Provides information about the structure of molecules. Utilized by Rosalind Franklin to obtain images of DNA.

Antiparallel nature of DNA

Complementary DNA strands run in the opposite directions. Form a double helix

H-DNA

Formed when DNA unwinds and one strand pairs with double-stranded DNA from another molecule. AKA triple stranded, triplex

Hairpin structure

Formed in single stranded nucleotides when sequences on the strands are inverted compliments.

Stem structure

Formed when complementary single stranded nucleotides are contiguous

Key characteristics of genetic material

Must contain complex information

Must replicate faithfully

Must encode the phenotype

Must have the capacity to vary

Meischer

Isolated the nuclei from WBC in pus and discovered a novel substance he called nuclein, later renamed nucleic acid by a student.

Kossel

Determined DNA contained four bases, Adenine, Cytosine, Thymine, and Guanine

Chargaff’s rules

Amount of A equals the amount of T, amount of C equals the amount of G

Griffith’s experiments

Demonstrated that a living nonvirulent bacteria mixed with a dead nonvirulent bacteria and injected into a mouse would result in the mouse dying, and living virulent bacteria being recovered.

Avery, MacLeod, and McCarthy

Performed an experiment that revealed Griffith’s transformative principle to be DNA

T2

Bacteriophage that infects E.Coli

Hershey and Chase

Demonstrated that DNA carries the genetic material in phages, not proteins

Watson and Crick

Discovered the 3 dimensional structure of DNA, 1953

Genetic information

Some viruses use RNA instead of DNA as this

Tobacco Mosaic Virus

Uses RNA as its genetic material. Made up of RNA and proteins. When Type A and Type B RNAs and proteins are mixed, the RNA determines the type of the new hybrid virus.

The primary structure of DNA

Consists of a string of nucleotides joined o\together by phosphodiester linkages.

Nucleotides

The repeating units of DNA. Comprised of three parts, a sugar, phosphate, and nitrogen containing base.

Pentose sugars

The 5 carbon sugars of nucleic acids. Differ slightly between DNA and RNA

Ribose

RNAs sugar. Contains a hydroxyl group at the 2’ carbon.

Deoxyribose

DNAs sugar. Contains one less hydroxyl group than ribose

Purine

six membered ring attached to a five membered ring. Purines in DNA and RNA are adenine and guanine

Pyrimidine

Consists of a six membered ring. Cytosine is found in DNA and RNA. Thymine is found in DNA. Uracil is found in RNA.

Phosphate

Phosphorus atom bound to four oxygen atoms.

Found in every nucleotide

Carries a negative charge, which makes DNA acidic

The secondary structure of DNA

Refers to its three-dimensional configuration, the helical structure.

The double helix

Two polynucleotide strands wound around each other

Hydrogen bonds

Link the bases on opposite strands

Easily broken

Phosphodiester bonds

Link the phosphate and sugar groups of adjoining nucleotides.

Backbone

Two hydrogen bonds

Adenine and thymine

Three hydrogen bonds

Cytosine and guanine

Complementary DNA strands

Strands are aligned so that complementary bases match.

B-DNA structure

DNA structure identified by Watson and Crick

Exists when the molecule is surrounded by plenty of water, and there are no unusual base sequences

Most stable, and likely predominant structure in the cell

Right handed helix

B-DNA. Clockwise spiral

A-DNA structure

Exists if less water is present.

Right handed helix

Shorter and wider then B-DNA

Z-DNA

Left handed helix

Sugar phosphate backbone zigzags

May play a role in gene expression, its proteins bind to DNA being transcribed into RNA

Special structures in DNA and RNA

Single strands of nucleotides my be complementary to one another and able to pair, producing a double stranded region.

Hairpin structure

Forms when the sequences of nucleotides on a single strand are inverted compliments. The stem is made up of the paired bases. The loop is made up of intervening unpaired bases.

Stem structure

When complementary sequences are contiguous, no loop is formed.

H-DNA

Three stranded (triplex) structure. Forms when DNA unwinds, and a single strand from one part of the molecule pairs with a double strand from another part.

Often occurs in long sequences of only purines or pyrimidines

Common in mammalian genomes

DNA methylation

Methyl groups are added to certain positions on nitrogenous bases.

In eukaryotes, often related to gene expression

Effects the 3d structure of DNA

5-methylcytosine

Formed in eukaryotic cells when cytosine bases are methylated.