Chapter 8 – From DNA to Protein

Old dead people to add to our “Important People” chart PersonOriginTime Frame Importance Frederick Griffith English1928“transformation principle” Oswald Avery Canadian1944Repeated Griffiths experiment – found DNA was transformed Hershey & Chase American1952Used bacteriophages to verify DNA is genetic material

Frederick Griffith

Oswald Avery

Hershey and Chase Hershey Chase

DNA is a long polymer made up of nucleotides 3 parts to a nucleotide 2. Deoxyribose (sugar) 3. Nitrogen base 1. phosphate group

4 nitrogen bases in DNA 1. Adenine (A) 2. Guanine (G) 3. Cytosine (C) 4. Thymine (T) Double Ring = Purines Single Ring = Pyrimidines

Old dead people to add to our “Important People” chart PersonOriginTime Frame Importance Erwin Chargraff Austro- Hungarian 1950Chargraff’s rule: A=T, G=C Rosalind Franklin BritishEarly 1950’s Took x-rays of DNA which showed an “X” shape Watson & Crick American / British 1953Made a model of DNA with a double helix shape

Erwin Chargraff

Rosalind Franklin

WatsonCrick Watson and Crick

The sugar and phosphate form the backbone of DNA The bases stick out sideways A always pairs with T Base pairing rule: G always pairs with C

Replication = the process by which DNA gets copied DNA gets made during the S phase, how? Possible because of base pairing rules

Each strand is now a template to build the other “half” Step 1: DNA helicase “unzips” DNA  creates a replication fork

Step 2: DNA polymerase adds free bases to each half of the “unzipped” DNA

The whole process is quick  it happens in hundreds of spots at once Also accurate because DNA polymerase “proofreads”

Central Dogma of biology = info flows one way; DNA  RNA  Protein

1. Ribose instead of deoxyribose RNA is like a disposable copy of DNA 2. Single strand instead of a double 3. Uracil instead of thymine 3 major differences

Transcription = copying part of DNA to make RNA Genes, not the whole chromo, get copied RNA polymerase help the process along

Step 1: RNA polymerase unwinds DNA at beginning of a gene

Step 2: RNA polymerase adds free bases to new RNA, DNA zips back together A pairs with U, C pairs with G

Step 3: New RNA detaches from DNA 3 types of RNA are the possible result; mRNA, rRNA, tRNA

RNA Type The letter?Its JobConstruction Analogy mRNAMessengerCopy of DNA instructions for cell’s use Blueprints for the building rRNARibosomalMakes up ribosomesThe actual build location tRNATransferTransfers the amino acids to the ribosome The workers bringing supplies

Once mRNA is made its translated into protein mRNA has 4 bases = 4 letters in its code Each “word” (codons) is 3 bases long There are 64 possible 3-base codons

Some amino acids have more than 1 codon 1 codon that acts as a start code 3 codons act as a stop

Step 1: mRNA in the cytoplasm attaches to a ribosome

Step 2: As each codon goes through the ribosome an amino acid is brought by tRNA tRNA has an anticodon that matches with the codon Ex. Codon ACG matches anticodon UGC

Step 3: Peptide bonds form between adjacent amino acids – tRNA is available to go get more supplies

Step 4: The amino acid chain grows until a stop codon

Mutations = changes in an organisms DNA Point mutations happen when one nucleotide is swapped for another Ex. Frameshifts – insertions/deletions

Chromosomal mutations involve changes in larger parts of the chromo Ex. Deletions, duplications, translocations

Mutations can be “neutral”, negative, or even beneficial Some disrupt normal activity Some cause genetic disorders Some cause cancer