DNA: Structure, Function & Replication

Background Understanding… DNA! What do we recall?? What type of macromolecule is DNA? What is the function of DNA?

DNA – Critical Molecule! 1.All cells in an organism have the same DNA! (skin, eye, muscle, etc.) 2.Stores genetic instructions for producing proteins. 3.Gene = segment of DNA that controls the production of a specific protein. 4.Found In the nucleus of Eukaryotic cells and cytoplasm of Prokaryotic cells.

Overall DNA Structure 1.Double stranded – like a ladder 2.Helix shape, coiled 3.Outside or backbone made of alternating phosphates and sugars 4.Inside or steps of “ladder” made of nitrogenous bases – stores actual genetic info

Subunit of DNA: Nucleotide 1.A nucleotide is the monomer for DNA. 2.Structure: –Phosphate –Deoxyribose Sugar –Nitrogenous Base 3.Looks Like:

Nitrogenous Bases 1.4 Types of Bases: –A = Adenine –T = Thymine –G = Guanine –C = Cytosine 2.A’s and T’s bond together. 3.G’s and C’s bond together.

ADENINE THYMINE GUANINE CYTOSINE

Anti-Parallel Structure of DNA: 1.DNA has two different “ends” 2.The 5’(prime) End has the phosphate “hanging off” 3.The 3’(prime) End has the sugar “hanging off”

What does “antiparallel” mean? 4.Anti-Parallel refers to the two strands in DNA being positioned in opposite directions. 5.In DNA, one Strand goes 5’  3’… and the other starts at 3’  5’… 6.The strands are upside down mirror images of one another! Important for replication! We will come back to this!

Let’s draw an example together!!

DNA is arranged into Chromosomes DNA Condenses during Cell Division… DNA winds up into Chromatin Chromatin further condenses into Chromosomes

Chromosome Highly condensed DNA that’s passed on from one generation of cells to another. Made up of two strands called chromatids.

Visual Learning! dCnU14https:// dCnU14

Gene Segment of DNA that codes for a specific protein Unit of heredity – passed from parent to offspring

DNA-related Structures … Smallest to Largest Nucleus  Inside of cell DNA Cell – Biggest! Smallest - Nucleotide – Makes up the DNA Chromosome

DNA Replication

Why Replicate DNA? 1.DNA replication is necessary for cell division. 2.Occurs during the S Phase of the Cell Cycle 3.Overall Goal: Make an identical copy of a DNA molecule for a new cell.

Replication Basics: Basic Steps: 1.Double helix is un-twisted. 2.Strands are separated. 3.Make a complementary copy of each strand. 4.Process is controlled by enzymes (proteins)

Semi-Conservative Replication Process = Semi-conservative Replication 1.Start with 1 molecule of double-stranded DNA 2.End with 2 molecules of double-stranded DNA 3.Semi-conservative = ½ of the original DNA molecule is conserved in each new molecule 4.End result: TWO double-stranded DNA molecules with: 1 old strand 1 new strand

Label! Double- stranded DNA molecule

Building complimentary DNA strands

1.First, the enzyme DNA helicase binds to the DNA and separates the strands 2.Then, to build the new strands the free nucleotide bases are paired with their complement on the original strand. 3.Remember – A’s bind with T’s and G’s bind with C’s

Remember  DNA Base Pairing: A—T –A = Adenine –T = Thymine G—C –G = Guanine –C = Cytosine

Free Nucleotides! There are free A’s, T’s, G’s, and C’s floating around in the cell. Like Legos in a bin –Think: It’s like free Legos hanging out in a bin, just waiting to get put together!

Building complimentary DNA strands