chapter 8 freshman honors biology semester two. discovery where does our inheritance come from?...
TRANSCRIPT
THE GENETIC CODE
Chapter 8
Freshman Honors Biology
Semester Two
Discovery
Where does our inheritance come from?Thought to be either DNA or proteinSeveral experiments were performed by
various scientists Conclusion: What molecule is the hereditary
molecule? Read p. 228 Hershey and Chase experiments.
1. What did they do?
2. What did they find out?
What does DNA look like?
Rosalind Franklin (1951)
Chargaff Noticed that the percentage of adenine and
thymine were similar in DNA samples Also, the percentages of cytosine and
guanine were similar Conclusion…?
Watson & Crick (1953) Won the Nobel Prize
for determining the structure of DNA
Proposed that it was a double helix with bases pairing in the middle (like a twisted ladder)
Nucleic Acid: Basic Structure
Nucleotide- monomer of a nucleic acid (polymer)
Three partsPhosphateSugarNitrogen Base
Phosphate
Sugar Nitrogen Base
DNA Nucleotide
= Phosphate = Deoxyribose
PURINES PYRIMIDINES
= Adenine
= Guanine
= Thymine
= Cytosine
DNA-Nitrogen Bases Pyrimidine
Single ring structure; C and T Purine
Double ring structure; A and G Base pairing
One purine and one pyrimidine Why does this work?
A = TG = C
A T
G C
DNA Structure Sugar-Phosphate
BackboneDouble strandedAlternating Inverted strands/anti-
parallelBase attached to
sugar Base Pairing
A pairs with TC pairs with GWeak Hydrogen bonds
hold them together
Nucleic Acids
Location of DNA
ProkaryotesFloating in cytoplasmOccurs as a ring
EukaryoteLocated in NucleusChromatin- form present during interphaseChromosomes- form present during
mitosis/meiosis
Chromatin and Chromosome StructureChromatin
DNA is coiled around histone proteins
Looks like a beaded necklace
Provides access to genes during interphase
Chromosome DNA is super-coiled Compacts the DNA for
more efficient movement Less chance of damage
or mistakes
DNA Replication DNA Formation of a new DNA molecule Occurs in the nucleus during S phase of
interphase Goal- to create a copy of every piece of DNA
before cell division Semi-conservative
Each original strand serves as a template Ending DNA molecules have one original strand and one
new strand
Process of DNA Replication DNA is unzipped
Done by an enzyme (helicase)Creates replication forksMany replication forks along length of DNA
strand
Process of DNA Replication (continued) Synthesis of new DNA strands
Done by enzyme (DNA polymerase)Occurs in opposite directions on the two strandsBases are added according to base pairing rules
(A-T and C-G)
Process of DNA Replication (continued) Finishing Touches
Backbone is sealed (done by enzyme: ligase)Proofread (done by enzyme: DNA polymerase)
RNA: The Other Nucleic Acid RNA Found in both the nucleus and the cytoplasm Also composed of nucleotides Functions to
Turn DNA instructions into a proteinRegulate gene function
Differences from DNASugar is ribose instead of deoxyriboseThymine is replaced with uracilSingle strand (backbone)
RNA NUCLEOTIDE
= Phosphate = Ribose
Purines Pyrimidines
= Adenine
= Guanine
= Uracil
= Cytosine
RNA STRUCTURE
•Single-stranded
Types of RNA All are made as copies of the DNA Messenger RNA (mRNA)
Single strand forms a stringCarries DNA instructions for 1 protein to the ribosome
Transfer RNA (tRNA)Single strand folds into clover leaf shapeCarries amino acids to the ribosome to build the
protein Ribosomal RNA (rRNA)
Single strand folds into 3D shapeCreates ribosome structure
Protein Synthesis: Central Dogma
DNA RNA Protein
TranscriptionDNA gene is transcribed (copied) into mRNA
mRNA bases are added by complementary base pairing rules
Occurs in nucleusDone by enzyme (RNA polymerase)
Separates DNA strands Uses one strand as template to base pair When finished, mRNA breaks off and DNA binds together
againmRNA is processedLeaves the nucleus through pores Travels to ribosome in cytoplasm
Complementary Base Pairing
DNA NitrogenBases
A=UT=AC=GG=C
RNA Nitrogen Bases
Translation mRNA is translated (decoded) into a
protein molecule at ribosome in cytoplasm mRNA instructions are read three bases at
a time- codon Every codon matches with a tRNA
anticodon tRNA is attached to a specific amino acid
(protein monomer) Amino acids are joined at the ribosome to
form a protein
Genetic Code Every mRNA codon
codes for a specific amino acid
This is called the genetic code
64 possible codons- only 20 amino acids
Start codon- AUG Stop codons-
UGA, UAA, UAG
Mutations Change to the genetic material Mutations within a gene
Point Mutation- occurs at one point in the DNA, changes one nucleotide○ Insertion- extra base added to gene○ Deletion- base removed from gene○ Substitution- one base is exchanged with another
Frameshift Mutation- moves all remaining bases forward or backward; changes all of the codons after it (insertion and deletion)
Mutations
Chromosomal Mutation Change in genetic material that can be seen
on a chromosomal level Duplication- part of a chromosome has been
repeated Deletion- part of a chromosome has been lost Inversion- part of a chromosome has been
flipped Translocation- part of a chromosome has
broken off and attached to another chromosome
Consequences of Mutations Some don’t do anything
Genetic change causes no change to protein
Protein change causes no change to function
Some are harmfulProtein change causes loss of function or
improper function
Gene Regulation
All somatic cells of an individual contain the same DNA
Different cell types just use different parts of the DNA library
Since these cells use different proteins, they look and act differently (cell specialization or differentiation)