NUCLEIC ACIDS

PROTEIN SYNTHESIS

GENETIC CODE

b PROGRAM OF THE CELL WHICH IS PASSED ON FROM GENERATION TO GENERATION

FREDERICKS & GRIFFITH EXPEPERIMENT

RESULTS

b THEORY:

• live harmless bacteria and the heat killed bacteria when mixed combined to form a harmful strain

b RESULTS:

• the molecule DNA was the transforming factor

– DNA: nucleic acid that stores and transmits the genetic information from one generation to the next

HERSHEY & CHASE EXPERIMENT

b Studies done on bacteriophages (viruses that attack bacteria

b labeled viruses with radioactive material to test whether the DNA or protein coat was involved

b RESULTS:

• DNA enters bacteria and the protein coat stays outside the bacteria

STRUCTURE OF DNA

b NUCLEOTIDE:

• PHOSPHATE GROUP

• NITROGENOUS BASE

– ADENINE (purine group)

– GUANINE (purine group)

– CYTOSINE (pyrimidines)

– THYMINE (pyrimidines)

• 5 CARBON SUGAR

b NUCLEOTIDES FORM LONG CHAINS

Building of a DNA molecule

b Crick and Watson - studied DNA structure (won Nobel Prize)

b Double Helix Structure:

• 2 twisted strands

• nitrogenous bases on each strand were opposite each other

• weak hydrogen bonds formed between bases

– adenine (A) bonds with thymine (T)

– cytosine (C) bonds with Guanine (G)

• number of bases paired equals each other

• this structure explains how DNA can replicate itself

REPLICATION OF DNA

b Each half of a DNA molecule serves as a template for making the other half

• an analogy would be a torn dollar bill

b each cell must duplicate its DNA before it can be passed on to the next cell

• replication: done by a series of enzymes that “unzip” the double helix, insert appropriate base pairs, produce sugar, phosphate links, and finally “proofread” results

summary

b DNA unzips

b hydrogen bonds are broken

b strands unwind

b each strand then acts as a template for complementary bases

• example: TACGTT makes ATGCAA

b 2 DNA molecules identical to each other are made

Summary of DNA Replication:

b In DNA replication…

b The strands of DNA separate, exposing the nucleotides.

b Free nucleotides from the cell will pair with the exposed strands…

b Bonds will form between the sugars

b The result is two complete double stranded DNA molecules…each has one original strand, and one new strand…

b See “Inside Story” on page 293.

RNA - ribonucleic acid

b DNA is the cookbook of life…It codes for the creation of proteins…

b Proteins in turn do all the work…

b The process of going from DNA code to actual proteins is called Protein Synthesis.

b DNA, however, is so valuable…you break it your busted…that the cannot risk having anything happen to it…

b So RNA is used…(ribonucleic acid)

RNA - ribonucleic acid

b Acts as a messenger between DNA and the ribosomes

b carries out the process of which proteins are made from amino acids

b becomes a disposable copy of DNA

b Structure:

• chain of nucleotides

• different than DNA

– sugar is ribose

– single stranded

– nitrogen bases are adenine, cytosine, guanine, and uracil

– A to U & C to G

• 3 different types

– mRNA - messenger

– tRNA - transfer

– rRNA - ribosomal

TRANSCRIPTION - RNA SYNTHESIS

b DNA is copied into a complementary strand of RNA

• DNA info => RNA info

b this needs to be done to get information out of the nucleus

• mRNA - does the job with the help of the enzyme Polymerase

Steps of Transcription

b RNA polymerase attaches to special places on the DNA molecule

b DNA is seperated from its double stranded structure

b RNA polymerase makes a mRNA strand which is a complementary to one DNA strand (base pairing)

b The starting and stopping of RNA polymerase is done by special codes in the DNA sequence

• example: AUG - starter codon

» UAA, UAG, UGA - stop codons

Transcription is similar to DNA replication…

b The DNA will unzip

b Free mRNA molecules will attach to the exposed DNA nucleotides based on the nitrogen bases…

b When the DNA is done being transcribed, the mRNA strand will detach itself, and the DNA will zip back together.

b The mRNA can then move out of the nucleus to the cytoplasm to find a ribosome.

PROTEIN SYNTHESIS

b Nitrogen bases contain information that directs protein synthesis

b DNA and RNA are needed

b Both DNA and RNA contain different bases

• DNA: A,T, C, G

• RNA: A, U, C, G

b 20 amino acids can be coded for if you combine 3 different nucleotides

b DNA nucleotides are copied onto mRNA strands (3 nucleotides = 1 codon)

• a codon codes for a specific amino acid

translation

b Decoding of mRNA into a protein

b translates nucleic acids into polypeptides

b mRNA doesn’t do this by itself

• tRNA - carries amino acids to ribosomes

• rRNA - makes up part of ribosomes

• ribosomes - protein synthesis

tRNA

b Decoding of mRNA into a message for an amino acid which can be transferred

• example: codon of mRNA AUG = methionine

b nucleotides of mRNA = nucleotides of tRNA

b codons => anticodons

b amino acids are decoded and tranferred to the polypeptide chain

ribosomes

b Help tRNA and mRNA

b consist of 2 subunits (1 large, 1 small)

• each subunit has rRNA and protein

b subunits of the ribosome bind to mRNA, initiator codon (AUG) links to the 1st anticodon of tRNA; thus signaling the start of chain

• tRNA an mRNA keep binding to make a long chain until it reaches a stop codon; then the ribosome falls off

– the ribosome is considered the final meeting place and “zips” the chain together

Summary of Translation:

b TRANSLATION begins…translation is the “reading” of the mRNA to create a protein.

b Proteins are made out of a series of amino acids

b The order of the amino acids tells what type of protein is made

b The ribosome’s job is to read the mRNA to determine what order to put the amino acids in.

Summary cont.

b To do this, the ribosome attaches itself to the mRNA strand.

b The ribosome works it way down the strand reading nucleotides in groups of 3

b A CODON is a group of 3 nucleotides.

b Each codon will code for a specific amino acid…

b However it is possible for several different codons to create the same amino acid…

Summary cont.

b The ribosome will match up tRNA with the bases on the original mRNA strand…

b Then the ribosome moves to the next set of 3, another tRNA and amino acid comes in…and so on…

b An amino acid string is made, the tRNA is released…leaving just a string of amino acids…

b Eventually one of the codon sequences will code for STOP…and the amino acid string is done…and released…

Genetic Changes

b Mutations: any change in the sequence of DNA (also changes the protein that it codes for)

• Mutations in reproductive cells can cause structural and functional problems in offspring

– The resulting offspring will have that mutation in every cell in its body…

• Mutations in body cells can change the cells ability to divide and function properly

– only that cell’s DNA is changed

– -However, that organism will not pass on the mutation to offspring.

Types of Mutations

b Point mutation: a change in a single base pair

• -Changing a single letter can change the entire meaning of the code:

– THE DOG BIT THE CAT

– THE DOG BIT THE CAR

• -However, the amino acid might still be coded (look at a.a. chart page 298)

Frameshift mutation

b Single base is added or deleted from the sequence

b This is much more serious than a point mutation.

• THE DOG BIT THE CAT

• (delete the G)

• THE DOB ITT HEC AT

b -Every codon after the insertion or deletion is changed…Very Bad!

Chromosomal mutation

b Incorrectly recombining of chromosomal sequences

b There are 4 main types of chromosomal mutations

• Deletion: Part of the chromosome is deleted

• Insertion: Part of the sister chromatid breaks off and is added to the other chromosome…doubling part of the chromosome

• Inversion: Part of the chromosome is turned around backwards.

• Translocation: Genes on one chromosome break off and attach to the wrong chromosome

Causes of Mutations

b Some are spontaneous – just happen

b Some are caused by a change in DNA by radiation, chemicals, or even high temperatures (mutagens)