BIOL-101 Lecture 11: Molecular Biology

Nucleotides are composed of

Pentose (5-carbon) sugar

Phosphate group

Nitrogenous base

Types of nitrogenous bases

Purines (A G)

Pyrimidines (C U T)

Purines

Adenine and Guanine

Pyrimidines

Cytosine, Uracil and Thymine

Bond strength of nucleotide base pairs

A and (T or U) have double bonds; C and G have triple bonds

Frederick Griffith

-Demonstrated transformation by changing genotype and phenotype of a cell by assimilation of genetic material from an outside source

-studied Streptococcus pneumoniae (R strain: non-pathogenic; S strain: pathogenic)

Oswald Avery, Maclyn McCarty, and Colin MacLeod

identified the "transforming agent" as DNA

By slightly tweaking Griffith's experiment by using heat-killed bacteria, purifying all chemicals from the cells (lipids, N.A., proteins), and adding each chemical to live cells

Hershey and Chase

Studied infected E. coli bacteriophages by tagging their proteins with radioactive isotopes of Sulfur and Phosphorus

Demonstrated that only DNA entered the bacterium

Chargaff's Rule

Proved the bondage of A=T, A=U, and C=G through chemical analysis

Wilkins and Franklin

Used X-ray crystallography diffraction to determine DNA shape

"Discovered" 3D DNA double helix (stole Rosalind Franklin's work)

Watson and Crick

Won Nobel Prize for determining the true structure of DNA: two strands of alternating deoxyribose and phosphate held together by H bonds between bases twisted into double helix; information is carried in long sequences of nitrogenous bases

Biological properties of DNA

Carries information generationally

Has to copy itself accurately

Sometimes mutates

Must be translated and its information put into action

DNA replication

Occurs during S phase of interphase

Located within nucleus of eukaryotic cell

Involves production of new DNA from existing DNA templates (semiconservative)

Helicase

Unwinds and unzips DNA helix

DNA polymerase

Builds a new DNA strand by adding complementary bases to single strand DNA template

Builds new bases to repair mistakes

Leading Strand vs. Lagging Strand

works toward replication fork / works away from replication fork; both always move in the 5' ➝ 3' direction

Leading strand

3' to 5' replicated continuously while moving in 5' to 3' direction

Lagging strand

A discontinuously synthesized DNA strand that elongates by means of Okazaki fragments, each synthesized in a 5' to 3' direction away from the replication fork (antiparallel) and connected by DNA ligase

Nuclease

Removes damaged DNA during synthesis

Central dogma

Flow of genetic material in a eukaryotic cell

DNA -[transcription]➝ RNA -[translation]➝ protein

Transcription

Production of RNA from single strand DNA template

Helicase unzips DNA helix, producing single strand DNA template at TATA box

1. Initiation- begins at TATA box, promotor region of DNA

2. Elongation- everything after TATA box is transcribed

3. Termination- terminator sequence of DNA that stops transcription

Codons

A three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal

RNA polymerase

Produces new RNA nucleotides from single strand DNA template

mRNA

Translated and produces proteins

tRNA

carries amino acids to the ribosome and matches them to the coded mRNA message

rRNA

Structural RNA that makes up the ribosome

Translation

Process by which mRNA is decoded and a protein is produced

tRNA carries amino acid with anticodon complementary to mRNA codon

Amino acids are linked by what bonds to build a protein (polypeptide)?

Peptide bonds

Ribosome structure

A site- accepts tRNA, delivering amino acid

P site- processes tRNA, growing an amino acid chain

E site- exit that releases previously used tRNA molecules

Start codon

AUG or methionine

Initiates translation

Stop codons

UGA, UAG, UAA

Stops translation and allows for release of new protein

Polyribosomes

Chains of ribosomes allow for production of many protein molecules

Point mutation (base substitution)

Silent mutation- doesn't change amino acid

Missense mutation- changes amino acid

Nonsense- stop codon forms, no protein results

Frameshift mutation

Alters base sequence after mutation

Base addition- shifts reading frame to the right

Base deletion- shifts reading frame to the left