How do we know DNA is the genetic material?

• Griffith and later Avery• 2 strains of pneumonia causing bacteria:

rough and smooth• TRANSFORMATION

How do we know DNA is the genetic material?

• Hershey and Chase• Bacteria and bacteriophages (viruses)• Radioactive sulfur and phosphorus

How do we know the structure of DNA?

• Chargaff’s rules – BASE-PAIRING RULES

How do we know the structure of DNA?

• Franklin• X-ray shows shape is two twisted strands

How do we know the structure of DNA?

• Watson and Crick• Build model of DOUBLE HELIX• Where are the bases?• Where are the sugars?• Where are the phosphates?

Structure of DNA• Polymer of nucleotides (monomer)• Nucleotide – sugar + phosphate + base– Sugar – deoxyribose– Bases – purines – 2 rings – adenine and guanine pyrimidines – 1 ring – cytosine and thymine

• Base-pairing rules – purine to pyrimidine! A bonds to T G bonds to C

Structure of DNA• Double helix– Double – 2 strands– Helix – a spiral

• Looks somewhat like a twisted ladder– Sides of ladder – sugar and phosphate– Steps of ladder – nitrogenous bases

• Nucleotides are held to each other by covalent bonds

• Bases are held together by hydrogen bonds

DNA REPLICATION• Precedes cell division: mitosis, meiosis, binary

fission– Occurs during interphase

• Replication – DNA copies DNA• CAN YOU SEQUENCE THE STEPS?• CAN YOU WRITE THE STEPS?• EACH NEW DNA MOLECULE CONSISTS OF ONE

OLD STRAND AND ONE NEW STRAND

PROTEIN SYNTHESIS• How does cell use DNA code to build protein?• 2 processes: TRANSCRIPTION and TRANSLATION

PROTEIN SYNTHESIS• Requires the help of many enzymes and RNA• RNA– Single stranded– Sugar : ribose– Nitrogenous bases: adenine, guanine, cytosine, URACIL – What are the base pairing rules?

• 3 types involved in protein synthesis1. Messenger RNA – mRNA2. Ribosomal RNA – rRNA3. Transfer RNA - tRNA

TRANSCRIPTION• Occurs in nucleus of eukaryotes – Where does it

occur in prokaryotes?• DNA is copied by messenger RNA• How does mRNA know where to begin copying?• Can you sequence the steps?• Can you write the steps?

TRANSLATION• Occurs in cytoplasm at the ribosome• messenger RNA is read (decoded) by the ribosome;

transfer RNA supplies the amino acids to build the protein (polypeptide)

• How does the ribosome know where the beginning and end of the message are?

• Can you sequence the steps?• Can you write the steps?• Do you know the base pairing rules?• Can you use a codon chart to determine the order of

the amino acids?

MUTATION• What is a mutation?• What is the difference between a point mutation

and a chromosome mutation?• Can you recognize and explain the effects of the

following point mutations?– Substitution– Frame shift (due to additon or deletion of a base)

MUTATION• Can you recognize and explain the effects of the

following chromosome mutations?– Deletion– Inversion– Translocation– Duplication

What is the significance of mutations?• Neutral• Disrupt cell function• Source of genetic variation – source of NEW

genetic information• Exploited by human beings to improve or

develop new plants and animals.– polyploidy

Chromosome Structure

• Can you distinguish between chromatin and chromosome? When is each seen in the cell?

• What are histones and nucleosomes?• How are prokaryotic chromosomes different

from eukaryotic chromosomes?• What are genes? Where are they located?

Editing of mRNA

• In eukaryotes the mRNA copy of DNA must be edited before it leaves the nucleus?

• Why?• What is removed from the mRNA? Introns or

Exons?

What do genes code for? What do these molecules do in cells?