What is DNA Instructions for making proteins Blueprint
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.
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: 1. Adenine 2. Thymine 3. Guanine 4. 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
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 G G A ENZYME A C C T
• Step 2: Free nucleotides bind to the complementary bases. T G G A A C G A T A C C T
Result: 2 Complete Strands! T G G A A C C T
Semiconservative Replication: one of the original strands is present in each new strand of DNA.
Protein Synthesis Transcription & Translation DNA to m. RNA to Protein
RNA • There are three kinds of RNA: 1. Messenger RNA (m. RNA): takes message from DNA in nucleus to the ribosomes in cytoplasm 2. Ribosomal RNA (r. RNA): makes up the structure of ribosomes 3. Transfer RNA (t. RNA): 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 m. RNA molecule • Similar to DNA replication, but only one new strand is made • m. RNA molecule leaves the nucleus & moves to the ribosome • Making m. RNA transcript is the first step in protein synthesis (DNA to m. RNA)
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 m. RNA that code for one amino acid • Anticodon: pairs 3 nucleotides in t. RNA that with m. RNA
Strand to be transcribed DNA
Strand to be transcribed DNA Transcription RNA Start codon Stop codon
Third base First base Second base
Strand to be transcribed DNA Transcription RNA Start codon Polypeptide Met Translation Lys Phe Stop codon
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 (m. RNA 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 t. RNA-binding sites Large subunit m. RNA binding site Small subunit P site A site
Translation: m. RNA to Protein – Ribosomes ‘read’ 3 base sequences of m. RNA at a time= codon – Each codon is the code for a specific amino acid – Codon on m. RNA complements anticodon of t. RNA carrying amino acids to the ribosome
Next amino acid to be added to polypeptide Growing polypeptide t. RNA anticodo ns m. RNA Codons
Translation • Requires three steps: 1) initiation, 2) elongation, 3) termination. 1. Initiation • Small ribosome subunit binds to m. RNA • All proteins begin with start codon AUG (methionine) and pairs with t. RNA anticodon UAC • Initiator t. RNA binds to P site on ribosome at the START codon • “A” site on ribosome is ready for t. RNA carrying next amino acid
Met Initiator t. RNA P site 1 m. RNA Start codon Small ribosomal subunit 2 Large ribosomal subunit A site
Translation Continued 2. Elongation • Adding amino acids to the polypeptide chain • t. RNA 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 t. RNA
Amino acid Polypeptide A site P site Anticodon m. RNA Codons 1 Codon recognition m. RNA movement Stop codon 2 New peptide bond 3 Translocation Peptide bond formation
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
Transcription DNA m. RNA polymerase 1 m. RNA is transcribed from a DNA template. Translation Amino acid 2 Each amino acid attaches to its proper t. RNA with the help of a specific enzyme and ATP. Enzyme ATP t. RNA Anticodon Large ribosomal subunit Initiator t. RNA 3 Initiation of polypeptide synthesis The m. RNA, the first t. RNA, and the ribosomal sub-units come together. Start Codon m. RNA Small ribosomal subunit
New peptide bond forming Growing polypeptide 4 Elongation m. RNA Codons A succession of t. RNAs add their amino acids to the polypeptide chain as the m. RNA is moved through the ribosome, one codon at a time. Polypeptide 5 Termination Stop codon The ribosome recognizes a stop codon. The polypeptide is terminated and released.
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