Structure and Function of DNA Ch. 13

DNA Encodes hereditary information. Located in the nucleus of a eukaryotic cell. Each chromosome is a macromolecule of DNA. All living things have DNA and use the same code! Shape is double helix.

Discovery of DNA Early 1900s scientists knew  chromosomes carry hereditary info  chromosomes made of DNA and protein But which substance was source of genetic info?

Nucleotides Subunits (monomers) of DNA = nucleotides 3 parts of nucleotides:  Nitrogenous base  Phosphate group  sugar

Four nitrogen bases: A,T,C,G Purines: Adenine Guanine Pyrimidines: Thymine Cytosine

Base Pairs Always A – T Always C - G Purines = double carbon rings Pyrimidines = single carbon rings

James Watson and Francis Crick Watson (American) worked with Crick (English) at Cambridge, England to discover the double helical structure of DNA  Two outside strands of P and sugar  cytosine = guanine (3 bonds)  adenine = thymine (2 bonds)  Discovery of DNA Structure Discovery of DNA Structure

Maurice Wilkins and Rosalind Franklin Rosalind Franklin's contribution

Double Helix The sugar/phosphate make the backbone Nitrogen bases are the rungs Ladder twisted to form double helix

Order of the bases gives the code for proteins.

Antiparallel- each side facing opposite direction

DNA Visualizations 3D structure of DNA Molecular Visualizations of DNA James Watson on DNA DNA Replication DNA structure

DNA Replication (S phase) 8/08-03_DNAReplication_1.jpg

DNA replication: Helicase enzyme uncoils DNA New complementary strand made, corresponds to bases on each original strand. (A-T) (C-G) Semiconservative = 1 new strand + 1 old See p. 301 in Holt textbook!

DNA replication animation DNA Replication visualization DNA replication (6/10) DNA replication short DNA Replication DNA replication Crash Course

Protein Synthesis The Human Genome Overview of Protein Synthesis

DNA

Overview of protein synthesis

Amino Acids: Subunits of protein are called amino acids Only 20 amino acids (a.a.) in all life Amino acids link together make different proteins.

Three bases code for 1 amino acid

Compare DNA and RNA DNARNA Deoxyribonucleic acid Ribonucleic acid Deoxyribose (sugar)ribose (sugar) A, C, G, TA, C, G, U (uracil) double strandedsingle stranded stays in nucleuscan move out of the nucleus

Three types of RNA:  Messenger RNA = mRNA  Transfer RNA = tRNA  Ribosomal RNA = rRNA

Making proteins 1. DNA is transcribed into mRNA in nucleus (transcription) 2. mRNA leaves nucleus and bonds to rRNA on ribosome in cytoplasm. 3.mRNA is then translated into proteins by ribosome. (translation) 4.tRNA brings in amino acids to be bonded together to make protein.

DNA transcription and protein synthesis

Transcription Copy DNA code into mRNA in nucleus. Uracil replaces thymine in RNA. (A-U) mRNA leaves nucleus and finds a ribosome in cytoplasm

Translation mRNA takes info to cytoplasm and bind to ribosome tRNA brings in amino acid & matches codon A.A. are linked to make protein.

Translation

Codon = 3 letter mRNA code for one amino acid

DNA Visualizations Molecular Visualizations of DNA

Overview of protein synthesis

DNA – The original drawing RNA – Copies or blueprints Amino Acid chain (protein) – the finished, functional product of a gene

Central Dogma DNA  RNA  Proteins

Gene Regulation: Ability of organism to control which and when genes are expressed (translated)

When things go wrong… Are mutations heritable? Are mutations beneficial/harmful/both? Are mutations the cause of evolution? What are mutations?

Find the base pairs that are incorrect in this strand of DNA. G G A T A T T A C C G T T G A A A G C A T C C G A T G A T G C C A A C T G G C G C A

Find the base pairs that are incorrect in this strand of DNA. G G A T A T T A C C G T T G A A A G C A T C C G A T G A T G C C A A C T G G C G C A ↑ ↑ ↑ ↑ ↑ ↑

Genetic MUTATION A change in the nucleotide sequence of a gene. ACU vs. AGU

SUBSTITUTION THE BIG FAT CAT ATE THE WET RAT THE BIZ FAT CAT ATE THE WET RAT

Sickle Cell Single nucleotide substitution Ex: in sickle cell disease, valine is substituted for glutamate (GUA for GAA)

DELETION  THE BIG FAT CAT ATE THE WET RAT  THB IGF ATC ATA TET HEW ETR AT Ex: cystic fibrosis

Cystic Fibrosis CTFR transmembrane protein Most common CF cause is deletion of 3 base pairs for phenyalanine

Normal CFTR Sequence: Nucleotide ATC ATC TTT GGT GTT Amino Acid Ile Ile Phe Gly Val F508 CFTR Sequence: Nucleotide ATC ATT GGT GTT Amino Acid Ile Ile Gly Val

INSERTION  THE BIG FAT CAT ATE THE WET RAT  THE BIG ZFA TCA TAT ETH EWE TRA Ex: Crohn’s disease

FRAMESHIFT MUTATIONS Insertion or deletion changes the reading frame: THE BIG FAT CAT ATE THE WET RAT THE BIG ZFA TCA TAT ETH EWE TRA T Now you’re making a completely different amino acid sequence!

DUPLICATION THE BIG FAT CAT ATE THE WET RAT THE BIG FAT FAT CAT ATE THE WET RAT

MUTAGENS Substances like chemicals and radiation that can damage DNA

Which mutations can be passed to offspring? Somatic or sex-cell mutations? Why?

Chromosome mutations Pieces of DNA can be deleted or moved to a different location on the chromosome or to another chromosome.