DNA Structure and function

Journey into the cell

Viruses – small nonliving particle that infects cells Not living because it can not reproduce without infecting a host cell. Made of a protein head and genetic material.

Bacteriophage – virus that infects and bacteria (bacteria eater) Made up of DNA and a protein coat. It injects it’s DNA into into the bacteria cell. It tricks the bacteria into thinking the viral DNA is its own.

Bacteria starts to make more viral DNA and then the cell bursts. Hundreds of new viruses are released.

A virus can take advantage because DNA is the universal genetic code for all living things. Viruses are usually specific in what cells they attack. For example, bacteriophages attack bacteria cells.

Hepatitis is a disease in which a virus attack liver cells in humans. HIV attacks T- helper cells of the immune system

Characteristic of DNA 1. carry information from one generation to the next. 2.puts that information to work by determining the inheritable characteristics of an organism. 3. has to be easily copied since all the DNA is replicated each time a cell divides.

DNA Structure: DNA is a long molecule made of nucleotides. Nucleotide 1. 5-carbon sugar (deoxyribose), 2. nitrogenous base, 3. and a phosphate group. Build a DNA molecule

This is considered to be one nucleotide: 1. One 5-carbon sugar (deoxyribose), 2. One of the four nitrogenous bases, 3. and a phosphate group.

Nucleotides

Nucleotide repeat over and over to make up one huge DNA molecule

The Double Helix The sides are repeating units of sugar and phosphate. The sugar being deoxyribose

The rungs of the ladder are the four bases: A, T, G and C Remember GCAT G bonds with C and A bonds with T Hydrogen bonds holds together the bases This is called base pairing.

First to see DNA Rosalind Franklin used X-ray diffraction to take a picture in the 1950s. She was able to see 2 strands of DNA in a helix shape.

Double Helix

Watson and Crick built the 3D double helix model of DNA that we use today They saw Rosalind Franklin’s x-ray photo to help guide them It showed the twisted ladder.

Watson and Crick

DNA is found inside the nucleus of most cells. It is found in the form of chromosomes. Every time a cell divides, DNA must make a copy of itself so that each cell has an equal amount of DNA

Chromosomes to DNA

Prokaryotic Cells =Lack nucleus and many organelles found in eukaryotes DNA is found in cytoplasm Plasmid: circular DNA segment

Eukaryotic Cells = DNA is found in nucleus in the form of chromosomes. Number of chromosomes varies from one organism to another Humans have 46, fruit flies has X more DNA than prokaryotic cells: more complex.

CHROMOSOME STRUCTURE DNA in Eukaryotes is packed tight. Nucleus contains more than 6 feet of DNA. Eukaryotic chromosomes have both DNA and proteins packed together to form a substance called chromatin Chromatins consist of DNA that is tightly coiled around proteins called histones. Histones = proteins that DNA wrap around.

DNA Chromosome Supercoils Coils Nucleosome Histones DNA double helix Section 12-2 Go to Section:

DNA Replication

DNA replication: Every time a cell divides, DNA must make a copy of itself. Reason: so every cell has an equal amount of DNA 46 chromosomes in humans.

Replication – duplicating or copying the DNA before the cell divides. How is it done? 1. Start with an original strand of DNA 2. DNA unzips between the paired bases and the DNA separates into 2 strands The hydrogen bond breaks between them A--T 3. Each separated strand gets copied to make two new strands.

The new strands are complimentary because they are formed according to base rules. G-C, A-T Complimentary strands of DNA have opposite bases.

Process: 1. Original DNA strand: ATATGGGCCATTT TATACCCGGTAAA 2. Original strand unzips: ATATGGGCCATTT TATACCCGGTAAA

3. Complimentary strands are created ATATGGGCCATTT TATACCCG….. ATATGGGCC…… TATACCCGGTAAA

You do this one: TACCCGGCCCTTT ATGGGCCGGGAAA

Each strand of the double helix serves as a templatefor the new strand. Template: model for the new DNA strand

DNA REPLICATION Section 12-2 Go to Section: Growth Replication fork DNA polymerase New strand Original strand DNA polymerase Nitrogenous bases Replication fork Original strand New strand

REPLICATION ns/dna_replication.htm

DNA replication interactive

In your own words: How is DNA replicated? ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ __________ BE READY TO SHARE WITH THE CLASS