DNA

Biomolecules – Remember Carbohydrates Lipids Nucleic acids – hold genetic information; code for proteins Proteins

History of DNA

Who Discovered DNA Rosalind Franklin James Watson & Francis Crick Took X-ray diffraction images In 1953 James Watson & Francis Crick Used Franklin’s image Developed the 1st accurate model of DNA

Overall Importance to Organisms Nucleic Acids Overall Importance to Organisms Stores and transmits genetic hereditary information Codes for proteins Gene- specific segment of DNA

Nucleic Acids DNA – double stranded genetic molecule RNA – single stranded genetic molecule

Basic Building Block- Nucleotide

Sugar part of Nucleic Acids DNA RNA

Base pairs in DNA: A – T and G – C Hydrogen bonds

Held together by H bonds

DNA Double Helix – “ Twisted Ladder” “Rungs” of ladder are Nitrogenous base pairs held together by weak Hydrogen bonds Adenine with Thymine Guanine with Cytosine Side of ladder Alternating Sugar and phosphate backbone

Antiparallel Strands Parallel Strands 5’ 5’ 3’ 5’ 3’ 3’ 5’ 3’ Antiparallel Strands Parallel Strands

Nucleosome

DNA  histones nucleosomes chromosomes Organization of DNA In chromosomes, DNA is wound around histones A nucleosomes is a cluster of 8 histones

Reason for Packaging DNA must be tightly wound in order to fit inside the nucleus or nucleoid region of a cell Uncoiled human DNA is about 6 feet long!

Summary of DNA Structure DNA is made of nucleotides as building blocks Nucleotides consist of deoxyribose (sugar), phosphate and a base DNA has a antiparallel double helix shape DNA is held together by hydrogen bonds DNA consists of two strands joined by complementary base pairs Adenine and Thymine (A-T) Guanine and Cytosine (G-C) A segment of DNA is called a gene, which codes for proteins

DNA Replication

Replication Replication – copying DNA for new daughter cell Occurs during S phase of cell cycle S for DNA Synthesis

Replication – copying DNA Replication – copying DNA to supply new cells with DNA copy DNA – instructions to make proteins and specialized cells

Base sequence The sequence of bases codes for proteins Ex. The strand you see now is ACAGGACGAC which may be the gene for the protein, keratin, in your fingernails That sequence of DNA would be the gene for keratin

Human DNA (As Chromosomes) 23 pairs of chromosomes 25, 000 genes

Growth – increase # of cells Replication is used to provide new cells with copy of DNA when new cells divide for Healing Replacement Growth – increase # of cells

Cancer – uncontrollable growth of cells Defect in their DNA that tells them to keep growing and dividing

Cancer Cells under Microscope

DNA Replication – What do you see?

Terms of Replication Helicase – enzyme that unwinds DNA DNA Polymerase – enzyme that adds nucleotides to DNA Parent strand – original DNA double helix Daughter DNA –DNA copies with one side from parent strand and one new side Replication fork – where DNA is unwound and separated into 2 single strands

Steps of DNA Replication – S phase Helicase carefully unwinds double helix of DNA, revealing replication fork DNA Polymerase adds complimentary nucleotides to the two original strands of unwound DNA Hydrogen bonds hold Adenine to Thymine, and Cytosine to Guanine Two new strands of DNA are formed, one for original cell, and one for new cell

Can you label the parts?

Helpful Videos http://sites.fas.harvard.edu/~biotext/animations/r eplication1.swf Flash –DNA Replication 3D animation https://www.dnalc.org/resources/3d/04- mechanism-of-replication-advanced.html Overview of DNA structure and replication https://www.youtube.com/watch?v=27TxKoFU2Nw

Mutations Actual Mutations in fruit flies

What Causes Mutations? Environment: a physical or chemical cause. Examples: UV light, radiation, drugs, and benzene. Mutagens are often also carcinogens – anything that causes cancer Can be natural, random events. - mutations occur in 1/100,000 DNA replications (DNA mistakes) Mutations do not have to be bad (evolution)

Mutations Mistakes made during replication If a mutation occurs in a sex cell, the mutation will be passed to offspring Examples: Down Syndrome A mutation is any change in a cell’s DNA Types of Mutations Point Mutations Substitutions Frame Shift (insertion and deletion)

Mutations on Chromosomes