Unit 4A DNA Structure and replication Click the star for the DNA Structure Video!! Unit 4A DNA Structure and replication

DNA (Deoxyribonucleic Acid) A nucleic acid Made up of nucleotides

DNA Nucleotide O O=P-O N CH2 O C1 C4 C3 C2 Phosphate Group Nitrogenous base (A, T, C, or G) CH2 O C1 C4 C3 C2 5 5-C Sugar (deoxyribose)

DNA is a molecule that must sometimes be copied. When/why does the DNA need to be copied?

What do pyrimidines have in common? __________________ How many different types of nitrogenous bases are found in DNA? __________________ What do pyrimidines have in common? __________________ What do purines have in common? _____________________ If each nucleotide contains 1 nitrogen base, how many different types of DNA nucleotides can be formed? ______ NOTE: Another type of nucleotide, Uracil (U), will replace the Thymine nucleotide in RNA molecules. 4 total in 2 categories

Here is an example of a nucleotide: We normally draw a nucleotide using symbols/letters to represent the parts. What does the "A" stand for? What other letters could be used in that position?___________ What does the "S" stand for?___________________________ What does the "P" stand for?___________________________ A S

Notice that each nucleotide bonds with a nucleotide above and below it Notice that each nucleotide bonds with a nucleotide above and below it. This forms a strand of DNA.   The two strands run in opposite directions. This is called antiparallel. The two strands are then twisted into a spiral shaped, double stranded structure called a double helix. Phosphate Group P

The bonds that hold the nucleotides in a strand of DNA together are covalent bonds (highlight) The bonds in between the nitrogenous bases that connect the two strand are hydrogen bonds (draw in color) Phosphate Group P

Circle a nucleotide on the drawing to the left What does each nucleotide have in common? How do nucleotides differ from each other? How many strands make up a molecule of DNA? ____ Adenine (A) pairs with _________ Cytosine (C) pairs with _________ Phosphate Group P

If the sequence of nucleotides in one strand of a DNA molecule is T-A-C-G-G-T-C-A-A, what would be the complementary base pairs on the other strand? ______________________________

Who discovered the structure of DNA? Erwin Chargaff (1950) Determined that the percent of A was about equal to the percent of T in any DNA molecule. Likewise, the percent of C was about equal to the percent of G. This is known as Chargaff’s Rule Why did he see this consistency?

Using Chargaff’s Rule Source of DNA A T C G Human 30 Percentage of Bases in Human DNA Source of DNA A T C G Human 30

Rosalind Franklin (1952) Used X ray diffraction Her image hinted that DNA was two stranded and in a helical shape

James Watson and Frances Crick (1953) Won the Nobel Prize for determining the structure of DNA Used info from Chargaff and Franklin James Watson Francis Crick

Human Genome Project (1990-2003) Genome: the entire set of genetic information that makes up the DNA of an organism Completed in 2003, the Human Genome Project (HGP) was a 13-year project coordinated by the U.S. Department of Energy and the National Institutes of Health.

Goals of the Human Genome Project identify all of the approximately 20,000-25,000 genes in human DNA determine the sequence of the 3 billion base pairs that make up human DNA store this information in databases for use by scientists everywhere address the ethical, legal, and social issues (ELSI) that may arise from the project.

DNA Sequencing the laboratory technique used to determine the exact sequence of A’s, T’s, C’s, and G’s in an individuals entire genome.

Human Genome Project What were three surprises for scientists after they sequenced the human genome? Fewer genes are in the human genome than once thought (20,000-25,000) Only 2% of the genome is actually genes Hasn’t helped to cure all diseases; DNA is not the only thing that dictates illness What were two good things that came from sequencing the human genome? New fields in biology were created to study genes (ex: genomics) Has given clues to our evolutionary history. (We still have the gene for a tail even though it is not used!)

Forms of DNA and How it is Organized Where is DNA located? Prokaryotic cytoplasm Eukaryotic nucleus Every body cell has a complete copy of DNA

Forms of DNA Prokaryotic- 1 circular loop Eukaryotic- multiple linear (straight) strands found in 2 forms depending on the situation. 1. Chromosomes 2. Chromatin

Forms of DNA (cont.) 1. Chromosome: tightly packed, or “condensed” strands of DNA. DNA forms these structures when the cell is dividing. Usually shown as an X-shape or doubled chromosome. Histones - Proteins which act like spools for thread. DNA is wound around the histones.

Karyotypes A picture of all of the chromosomes from one cell of an organism. How many total chromosomes are in the karyotype? These chromosomes are from a _________________.

Number of Chromosomes in each cell. Every species of eukaryotic organisms have a specific number of chromosomes in each cell: Organism Number of Chromosomes in each cell. goldfish 94 chicken 78 horse 64 sand dollar 52 chimpanzee 48 dog human   brown bat 44 corn plant 20 housefly 12 fruit fly 8

How many chromosomes do humans have? _______  How long is the DNA in one human cell?__________ How does that much DNA fit into a cell? 1-3 meters

Forms of DNA (cont.) 2. Chromatin - loosely packed, or “working” form of DNA. The strands are loose and exposed so that the code or protein “recipes” can be read and proteins can be synthesized.

Why have 2 different forms of DNA in your cells? Chromosomes are useful because  they are condensed and easy to sort and move when cells are dividing to make new cells. Chromatin is useful because   it is loose/open so genes can be read to make proteins (like an open book) Why is the number of chromosomes different for different organisms? Chromosomes are different sizes Chromosomes have different numbers of genes 3) Organisms need different proteins and amounts for different functions.

DNA Replication DNA must be copied before cell division so that any new cells will have an IDENTICAL copy of the DNA from the original cell.

Steps in DNA replication:   1. The enzyme DNA helicase unwinds and unzips the double helix and the 2 DNA strands are separated between the complementary nitrogenous bases.

2. The enzyme DNA polymerase helps to link free floating DNA nucleotides with the complementary nitrogenous bases on each of the two strands

3.) Covalent bonds join the nucleotides above and below each other on the new strands. And, the hydrogen bonds are formed between the complementary nitrogenous bases (from one strand to another).

4.) Each new DNA strand formed contains ONE parent (original) strand and ONE daughter (new) strand.

Summary of Replication DNA double helix splits into two strands Each strand becomes a template for new nucleotides to bind Base pairing allows for the correct sequence to be created on the new “complementary” strand Replication

If an error is made during replication it is called a mutation.