Chapter 8 How Cells Reproduce

Macromolecule:Nucleic Acid

There are two Nucleic Acid Macromolecules1. DNA =Deoxyribonucleic Acid “instruction book for the cell” this cannot leave the nucleus!2. RNA = Ribonucleic Acid “reads, copies, and carries it’s version of the instructions out of the nucleus to the cell to be used”

DNA

DNA is DOUBLE STRANDED it has two “sides” the bases in the middle are connected with hydrogen bonds**hydrogen bonds are weak and easily broken*The TWISTED SHAPE is called a HELIX

DNA is a DOUBLE HELIX shape

Where is DNA found?

• DNA is in the nucleus of every cell in your body.

• (it is found in every cell of any living thing)

• DNA structure is the same for every living thing on the planet!

Basic DNA Structure: Double Helix

The bases in DNA are:Adenine , Thymine, Cytosine, GuanineThey form “base pairs” A-T C-G This pairing is called Chargraffs Rules

Purine and pyrimidine bases

• This is the actual chemical structure:

Look at the shape of the bases --------->>A, G are 2 circlesPurines

C,T are one circlePyrimidines

Nucleotides3 parts:-Phosphate-Sugar-Nitrogenous Base

Nucleotides put together in long lines become nucleic acids.

So what makes a plant differentfrom a human?

• Nucleotides are the segments of DNA that include a base.

• The arrangement of these nucleotides and the bases on them are what determines what makes things different.

• ALSO, the number of nucleotides can be different from SPECIES to SPECIES (plant to human, for instance)

What is a chromosome?

• A chromosome is DNA that is coiled up tightly into rod shaped structures.

Where are chromosomes in a cell?

• Chromosomes are only found in the nucleus of a cell when the cell decides to divide into two cells.

• At all other times, the nucleus contains DNA in long double helix strands called “chromatin” in a stage called INTERPHASE

Parts of a chromosome

How do we know so much about chromosomes?

• Scientists can take pictures of them!1. Look in the microscope and find a cell that

has started to divide and has coiled the DNA into chromosomes.

2. Take a picture of that cell.3. Enlarge the picture so you can see it better.4. Cut out the chromosomes and lay them out

on paper. Compare them to other cells.

Karyotype = a picture of chromosomes

• It looks like this:

This one has a problem: Down’s syndrome

Kleinfelter’s Syndrome