Bio DNA Test

Genetic Material Must Be:

-Able to store information for development, structure, and metabolic activities of cell/organism
-Stable for accurate replication and transmission
-Able to undergo mutations to provide genetic variability

Frederick Griffith

A bacteriologist who concluded that virulence could be passed form a dead strain to a non-virulent living strain

Details of Griffith’s Study

Injected a virulent but dead virus and a non virulent but living virus into a mouse, the mouse died and living lethal virus was taken from the dead mouse

Oswald Avery

A scientist who discovered that DNA is the transforming substance and genetic material

Details of Avery’s Study

With the heat-killed S strain bacteria, found that:

-the addition of DNase prevents transformation

-adding proteinase or RNase has no effect on transformation

Alfred Hershey and Martha Chase

Used a virus containing radioactive DNA and capsid coated proteins to inject a bacteria

Conclusion of Hershey and Chase’s Study

-After injection, bacteria were transformed and there was still presence of the DNA, but not of the protein
-Concluded that DNA MUST be the genetic material

Erwin Chargaff

Researched and concluded that:
-The amount of A,T,G, and C in DNA varies between species
-In each species, the amount of A=T and the amount of G=C

Rosalind Franklin

Studied and generated an image of DNA fibers with X-Ray diffraction

Found that DNA is a double helix

James Watson and Francis Crick

Were unsuccessfully trying to build a model of DNA (before Franklin’s discovery)
They were then able to construct an accurate model fitting the picture and Chargaff’s rules

DNA Structure

-2 Antiparallel strands of DNA
-A is bonded to T (hydrogen bond)
-G is bonded to C (hydrogen bond)
-Purines bond with Pyrimidines, creating a uniform shape
-Backbones of strands made from sugar and phosphate

Semiconservative Replication

DNA replication is semiconservative because each new DNA double helix contains an old strand form the parental DNA as well as a new synthesized daughter strand

Replication Step 1: Unwinding of the DNA

-DNA helicase unwinds DNA and separates the parental strands (creates 2 replication forks that move away from each other)
-Separate strands become templates for 2 new DNA molecules
-Single stranded binding proteins help by attaching to newly separated DNA and prevent it from re-forming a helix

Replication Step 2: Complementary Base Pairing

-DNA Primase places primers

-DNA Polymerase begins synthesizing new DNA with RNA primers(nucleotides form complementary base pairs with the original strand)
-DNA Polymerase corrects mistakes

Replication Direction

Occurs in a 5’ to 3’ direction
-Leading strand is exposed that 5’ to 3’ is easy
-The lagging strand must be synthesized in the opposite direction, so it has short segments with many starts and stops (okazaki fragments)

Replication Step 3: Termination

-DNA polymerase converts the primers into DNA
-DNA Ligase “glues” all of the Okazaki Fragments

-Results in 2 double helix models that are identical to each other and the original

Gene Expression

The process/flow of info from DNA to RNA to an expressed protein

Structure of RNA

-RNA is made up of Adenine, Guanine, Cytosine, and Uracil

-Single-stranded (doesn’t form a double helix)

Messenger RNA (mRNA)

A copy of the message in DNA that can be taken from the nucleus to ribosomes

Transfer RNA (tRNA)

A molecules that carries and transfers amino acids to the ribosomes

Ribosomal RNA (rRNA)

A part of the ribosome where polypeptides are formed)

Gene Expression Steps

Transcription: mRNA molecules is produced based on a DNA template
Translation: mRNA transcript is read by a ribosome and converted into a series of amino acids

Genetic Code

Coding Unit (Codons) MUST be 3+ nucleotides long, fewer doesn’t provide enough variety for 20 different amino acids

Features of Genetic Code

-It’s degenerate so most amino acids have 1+ codon (protects against mutations)
-It’s unambiguous so each codon has only 1 meaning
-It has start and stop signals telling when to begin and end translation (1 start, 3 stop codons)

Strands in Transcription

Template Strand: Serves as the template for transcription
Coding Strand: Sequence will be the same as the new RNA molecule

DNA to RNA Pairing

C: G
A: U
T: A
G: C

RNA Polymerase

The enzyme that synthesizes the RNA in transcription (brings the correct nucleotides to the site)

Transcription Stage 1: Initiation

-RNA Polymerase binds to a promoter

-Promoter defines the start point, direction, and strand for transcription

Transcription Stage 2: Elongation

-As RNA reads the template strand, the mRNA increases in size
-DNA-mRNA isn’t stable, only the newest part binds to DNA while the rest dangles

Transcription Stage 3: Termination

-When RNA polymerase reads the sequence, it finishes transcribing
-the mRNA is released from RNA polymerase and it becomes an mRNA transcript

RNA Processing

mRNA transcript is modified before leaving the nucleus:
-receives a cap at the 5’ end
-receives a tail at the 3’ end
-non-protein coding sections (introns) are removed
-protein-coding sections (exons) remain

Translation

The sequence of codons in the mRNA transcript are read by a ribosome

-The ribosome connects the correct sequence of amino acids into a polypeptide
-DNA/RNA info is converted into Protein

Transfer RNA (tRNA) Role

Transfers amino acids to the ribosome

Ribosome Role

-The ribosome is the site of protein synthesis in a cell

-rRNA is packaged with proteins into 2 ribosomal subunits
-binding site for mRNA transcript and 3 for tRNA molecules
-Ribosome moves along the mRNA transcript and creates a bond between amino acids that are brought together

Translation Step 1: Initiation

All components of translation are brought together

Translation Step 2: Elongation

-Polypeptide increases by each amino acid
-tRNA molecules move through the 3 binding sites of the ribosome

-Starts at A site where codon and anticodons are matched
-Moves to P site where amino acid is connected from the tRNA to the polypeptide
-Moves to E site where it will exit the ribosome

Translation Step 3: Termination

The completed polpypeptide and ribosome separate

-Occurs at stop codon where a release factor cuts away the polpypeptide