What is DNA? Instructions for making proteins ‘Blueprint’ for who we are Where is it found? Found in the nucleus What does ‘DNA’ stand for? Deoxyribonucleic Acid

The Structure of DNA Double helix Structure of DNA: Twisted Ladder

Who Discovered DNA’s Structure? SCANDAL! Read all about it! Rosalind Franklin, James Watson, Francis Crick, & Maurice Wilkins discovered the shape (double helix) of DNA is 1953.

DNA is a polymer of Nucleotides. What are the 3 parts of a nucleotide? THINK! DNA is a polymer of Nucleotides. What are the 3 parts of a nucleotide?

Nucleotides DNA Subunit 3 components a sugar a phosphate group a nitrogen base

Nitrogen Bases 4 Types: Adenine Thymine Guanine Cytosine REMEMBER: At The Golf Course

Complementary Base Pairs Nitrogen bases always pair with the same partner Adenine & guanine are double-ringed structures and are called purines. Thymine & cytosine are single ringed and are called pyrimidines. Hydrogen bonds hold the bases together. A--T (At--The)G-C (Golf--Course)

THINK! What would the complementary strand be? A-T-C-C-G-T-T-T-A-C-A-G-G-A T-A-G-G-C-A-A-A-T-G-T-C-C-T

Nucleotides join to form long chain (polymer) Sides of the ladder: How DNA Strands Form Nucleotides join to form long chain (polymer) Sides of the ladder: Sugar + Phosphate Rungs of ladder: Nitrogen bases bond together

How is DNA Organized? Histone proteins act like spools that wind up DNA to keep it organized.

During Interphase… How does DNA exist? Unwound! (Chromatin)

Why Chromatin? What happens during Interphase? DNA Replicates! DNA is uncoiled so that enzymes can unzip it. When it is unzipped, DNA can be duplicated.

DNA Replication Process where DNA is copied Occurs before mitosis and meiosis (during interphase!)

How DNA Duplication Occurs Step 1: Enzymes unzip the DNA strand T A G C ENZYME

Step 2: Free nucleotides bind to the complementary bases. G C

Result: 2 Complete Strands! G C

Semiconservative Replication: one of the original strands is present in each new strand of DNA.

Transcription & Translation DNA to mRNA to Protein Protein Synthesis Transcription & Translation DNA to mRNA to Protein

RNA There are three kinds of RNA: Messenger RNA (mRNA): takes message from DNA in nucleus to the ribosomes in cytoplasm Ribosomal RNA (rRNA): makes up the structure of ribosomes Transfer RNA (tRNA): transfers amino acids to ribosome to be assembled into a protein

Nucleus RNA transcription Enzyme RNA polymerase copies a strand of DNA into a complementary mRNA molecule Similar to DNA replication, but only one new strand is made mRNA molecule leaves the nucleus & moves to the ribosome Making mRNA transcript is the first step in protein synthesis (DNA to mRNA)

The Genetic Code DNA contains the code to make proteins Triplet: 3 nucleotides in a row in DNA that codes for one amino acid Codon: 3 nucleotides in mRNA that code for one amino acid Anticodon: 3 nucleotides in tRNA that pairs with mRNA

Strand to be transcribed DNA Figure 10.8B Deciphering the genetic information in DNA.

Strand to be transcribed DNA Transcription RNA Figure 10.8B Deciphering the genetic information in DNA. Start codon Stop codon

Second base First base Third base

Strand to be transcribed DNA Transcription RNA Figure 10.8B Deciphering the genetic information in DNA. Start codon Stop codon Translation Polypeptide Met Lys Phe

Ribosomes No membrane Made of 1 small and 1 larger subunit Constructed by nucleolus Ribosome is essentially a ‘big enzyme’ RNA translation : the rest of the process of making proteins (mRNA to protein) There are 20 different amino acids The order and number of amino acids in the protein make one protein different from another protein

The Ribosome tRNA-binding sites A site P site Large subunit mRNA tRNA-binding sites A site P site Large subunit mRNA binding site Small subunit

Translation: mRNA to Protein Ribosomes ‘read’ 3 base sequences of mRNA at a time= codon Each codon is the code for a specific amino acid Codon on mRNA complements anticodon of tRNA carrying amino acids to the ribosome

Next amino acid to be added to polypeptide Growing polypeptide Next amino acid to be added to polypeptide Growing polypeptide anticodons tRNA mRNA Figure 10.12C A ribosome with occupied binding sites. This figure shows that one of the tRNA binding sites (P site) holds the growing peptide chain while the adjacent site (A site) holds the tRNA carrying the next amino acid to be added to the chain. Codons

Translation Requires three steps: 1) initiation, 2) elongation, 3) termination. Initiation Small ribosome subunit binds to mRNA All proteins begin with start codon AUG (methionine) and pairs with tRNA anticodon UAC Initiator tRNA binds to P site on ribosome at the START codon “A” site on ribosome is ready for tRNA carrying next amino acid

Met Met Large ribosomal subunit Initiator tRNA P site A site Start Met Met Large ribosomal subunit Initiator tRNA P site A site Start codon mRNA Small ribosomal subunit 1 2

Translation Continued 2. Elongation Adding amino acids to the polypeptide chain tRNA carries next amino acid in to the A site Peptide chain is transferred (translocation) to amino acid in A site Then the polypeptide chain in A site slides over to the P site New codon on A site is ready to receive next tRNA

Amino acid Polypeptide P site A site Anticodon mRNA Codons 1 Codon recognition mRNA movement Stop codon 2 Peptide bond formation New peptide bond 3 Translocation

Translation Finished 3. Termination Ribosome comes to stop codon (UAA, UGA, or UAG) Release factor binds to A site Ribosome separates into its two subunits Polypeptide is released

polypeptide synthesis Transcription DNA mRNA is transcribed from a DNA template. 1 mRNA RNA polymerase Amino acid Translation Each amino acid attaches to its proper tRNA with the help of a specific enzyme and ATP. 2 Enzyme ATP tRNA Anticodon Initiator tRNA Large ribosomal subunit Initiation of polypeptide synthesis 3 The mRNA, the first tRNA, and the ribosomal sub-units come together. Start Codon Small ribosomal subunit mRNA

to the polypeptide chain as the mRNA is moved through the ribosome, New peptide bond forming Growing polypeptide 4 Elongation A succession of tRNAs add their amino acids to the polypeptide chain as the mRNA is moved through the ribosome, one codon at a time. Codons mRNA Polypeptide 5 Termination The ribosome recognizes a stop codon. The polypeptide is terminated and released. Stop codon