The Role of DNA, DNA Replication and Protein Synthesis

The Role of DNA Storing information – genetic information stored within the double helix inside the nucleus Copying information – replicate DNA during mitosis/meiosis (passes info on to new generation of cells) Transmitting information – Synthesize mRNA from DNA template to make proteins

Molecular Basis of Heredity

DNA Structure & Chemical Make-up 5 end Hydrogen bond 3 end 1 nm 3.4 nm 3 end 0.34 nm 5 end Key features of DNA structure Partial chemical structure Space-filling model

DNA Molecule Genes are made up of molecules of DNA: “Deoxyribonucleic acid” Found in nucleus. Controls manufacture of enzymes, proteins Made up of repeating subunits known as nucleotide subunits.

The nucleotide is made of 3 “parts” } 1. Phosphate group A sugar, called “deoxyribose” Nitrogenous base (the “rungs of the ladder”) (“sides” of the ladder)

Note: 5’-3’ arrangement, Hydrogen bonds between bases, NUCLEOTIDE = base, Phosphate group and sugar (deoxyribose) Thymine (T) Adenine (A) Cytosine (C) Guanine (G) DNA nucleotide

Nucleotides - DNA Adenine “A” (always pairs with “T”) Nitrogenous base: Adenine “A” (always pairs with “T”) Thymine “T” (always pairs with “A”) Guanine “G” (always pairs with “C”) Cytosine “C” (always pairs with “G”) Forms the “rung” of the ladder

DNA Replication During reproduction DNA makes exact copies of itself called REPLICATION. Occurs in nucleus during both mitosis and meiosis. TEMPLATE: Each side serves as a pattern or template (semi-conservative). Each base pair will attract the complementary nucleotide A—T or G—C

In a nutshell…DNA Replication – NOTE base-pairing rules: A-T, G-C The nucleotides are connected to form the sugar-phosphate back-bones of the new strands. Each “daughter” DNA molecule consists of one parental strand and one new strand. The parent molecule has two complementary strands of DNA. Each base is paired by hydrogen bonding with its specific partner, A with T and G with C. The first step in replication is separation of the two DNA strands. Each parental strand now serves as a template that determines the order of nucleotides along a new, complementary strand.

DNA Replication…the big picture

DNA Replication requires HELP! Helicase (enzyme) – separates the two strands of DNA SSB (single strand binding protein) – keeps DNA from coiling back up DNA Primase (enzyme) – marks the spot on DNA where replication will start DNA polymerase (enzyme) – lays down complementary nucleotides to exposed template and proofreads Ligase (enzyme)– ‘glues’ the new DNA strands together

As you can see, there are a lot of ENZYMES involved! The nitty gritty

Central Dogma of Biology

TYPES of RNA Type of RNA Functions Messenger RNA (mRNA) Carries information specifying amino acid sequences of proteins from DNA to ribosomes (disposable copy of recipe) Ribosomal RNA (rRNA) Makes ribosomes Transfer RNA (tRNA) Transfers amino acid to ribosome to assemble polypeptide (which will become a final protein)

Transcription (DNA RNA) Note: Base-pairing rules: DNA mRNA T A A U G C C G

Translation – reading the mRNA and assembling the polypeptide How do we “read” the mRNA? 3-letter CODONS (AUG) What does the CODON say? Identifies the AMINO ACID needed. How does the amino acid get to the ribosome? tRNA How does the ribosome know it’s the right tRNA? tRNA has the ANTICODON to the mRNA codon

Protein Synthesis Summary