Chapter 12 Freshman Biology Semester Two

Discovery  Where does our inheritance come from? Thought to be either DNA or protein Several experiments were performed by various scientists Conclusion: DNA is the molecule that provides heredity  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 parts Phosphate Sugar Nitrogen Base Phosphate Sugar Nitrogen Base

DNA Nucleotide = Phosphate = Deoxyribose PURINESPYRIMIDINES = 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 = T G = C AT GC

DNA Structure  Sugar-Phosphate Backbone Double stranded Alternating Inverted strands/anti- parallel Base attached to sugar  Base Pairing A pairs with T C pairs with G Weak Hydrogen bonds hold them together

Nucleic Acids

Location of DNA  Prokaryotes Floating in cytoplasm Occurs as a ring  Eukaryote Located in Nucleus Chromatin- form present during interphase Chromosomes- form present during mitosis/meiosis

Chromatin and Chromosome Structure Chromatin  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 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 forks Many 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 strands Bases 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 RNA  Found in both the nucleus and the cytoplasm  Also composed of nucleotides  Functions to Turn DNA instructions into a protein Regulate gene function  Differences from DNA Sugar is ribose instead of deoxyribose Thymine is replaced with uracil Single 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 string Carries DNA instructions for 1 protein to the ribosome  Transfer RNA (tRNA) Single strand folds into clover leaf shape Carries amino acids to the ribosome to build the protein  Ribosomal RNA (rRNA) Single strand folds into 3D shape Creates ribosome structure

Protein Synthesis: Central Dogma DNA RNA Protein

Transcription DNA gene is transcribed (copied) into mRNA  mRNA bases are added by complementary base pairing rules Occurs in nucleus Done by enzyme (RNA polymerase)  Separates DNA strands  Uses one strand as template to base pair  When finished, mRNA breaks off and DNA binds together again mRNA is processed Leaves the nucleus through pores Travels to ribosome in cytoplasm

Complementary Base Pairing DNA Nitrogen Bases A=UA=U T=AT=A C=GC=G G=CG=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  Type 1: Gene Mutation 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 Mutations

Type 2: 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 harmful Protein 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)