The Structure and Function of DNA
1. DNA is our genetic code!!! It is passed from generation to generation. It carries information that controls the functions of our cells. DNA stands for deoxyribonucleic acid.
DNA’s Structure: It is a polymer (long chain of the same molecule) called nucleotides! Nucleotides: building blocks of the DNA molecule. Every nucleotide has three parts: 1. phosphate group 2. sugar group 3. nitrogenous base
***The only variation among the nucleotides is what base is attached to each. The four nitrogenous bases (has nitrogen (N)) in DNA are… Adenine (A) Thymine (T) Cytosine (C) Guanine (G)
Franklin’s x-ray images suggested that DNA was a double helix of even width. James Watson and Francis Crick used Rosalind’s images to determine that DNA is a double helix made up of a sugar- phosphate backbone and nitrogenous base pairs on the inside.
Chargaff’s Rule: in every DNA double helix the #A = #T and the #C = #G. Example: -A-G-C-A-A-T-C- T-G- -T- C-G-T-T- A-G-A-C- Chargaff’s rule teaches us that… adenine always bonds to thymine. guanine always bond to cytosine.
The shape of a DNA molecule is a double helix. Nitrogenous Bases Deoxyribose Sugar and Phosphate (Rungs) (Backbone) (Hydrogen Bonds) (Covalent Bonds) *Bases pairs form the rungs of the ladder with hydrogen bonds. *Sugars and phosphates form the sides of the ladder with covalent bonds.
Chromosomes, DNA, and Genes! Nucleotides DNA Genes Chromosomes https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcRf9zJAGXryMcd15JSWPYxZPMco_oLtOaHhPvwayRpSJv2T3wTe
Human Genome The order of bases on ALL 23 pairs of human chromosomes. This allows us to know the specific location on a chromosome at which the DNA codes for a specific protein.
Be able to identify… -the deoxyribose groups -the phosphate groups -the nitrogenous bases -the hydrogen bonds -The covalent Bonds
Practice Problem 1: What is the complementary Base Pair for the following single stranded sequence of DNA? -A-C-G-T-C-C-G-A-A-T-
Practice Problem 2: In a sample of yeast DNA, 31 Practice Problem 2: In a sample of yeast DNA, 31.5% of the bases are adenine (A). Predict the approximate percentages of C, G, and T. Explain.
DNA Replication DNA Replication – When DNA makes a copy of itself! 2 complete and identical sets of genetic information are produced. The cell does this process before it divides
Step 1: Unzip the double Helix. Enzyme Used: Helicase Step 1: Unzip the double Helix Enzyme Used: Helicase How: Hydrogen bonds are broken This allows that both strands of the DNA can be copied at the same time.
The leading strand creates a continuous polymer. Step 2: Each existing strand of the DNA molecule act as a template for a new strand (the leading and the lagging strand). The leading strand creates a continuous polymer. The lagging strand creates short fragments that are later joined together. DNA Polymerase finds a starting sequence of nucleotides (the origin of replication) on each template. There can be multiple DNA polymerases on the same strand of DNA
DNA polymerases Enzymes that form bonds between nucleotides during replication. DNA polymerase “proof-reads” DNA sequences and replaces bad nucleotides.
Step 3: Free-floating nucleotides base pair with the exposed bases on each template strand. DNA Polymerase helps to guide this process The free floating nucleotides will hydrogen bond to the template strand.
Step 4: DNA polymerases covalently bond the deoxyribose sugar and phosphate between adjacent nucleotides to form a continuous new strand. Another enzyme Ligase help with this process on the lagging strand (and to help fix any errors).
Step 5: 2 identical double-stranded DNA molecules are produced. Each DNA molecule contains an original strand and one new strand.
Replication is fast and accurate In human cells, about 50 nucleotides are added every second to a new strand of DNA at the point of replication.
Replication Videos (and more) DNA Replication: https://www.youtube.com/watch?v=Cw8GAPuhAk4 Amoeba Sisters: https://www.youtube.com/watch?v=5qSrmeiWsuc (start at 1:59)