Structure and Function

What do the letters DNA stand for?◦ Deoxyribonucleic acid

Where is DNA located? ◦ Prokaryotic cells: in the cytoplasm◦ Eukaryotic cells : in the nucleus

How many pieces of DNA are in cells?◦ Prokaryotic cells: one, circular piece of DNA◦ Eukaryotic cells: several, linear pieces of

DNA (46 in humans)

What is a chromosome?

What does a chromosome look like?

A. Prokaryotic cells: circular in form

1) chromosome: ◦ tightly packed strands of DNA found in

a dividing cell. ◦ Usually shown as a doubled

chromosome, or X-shape

You have __46______ chromosomes in your body cells.

Each piece is about __5______ cm long. What is the total length of DNA in one body

cell? 3_ meters! (9 ft)

How does that much DNA fit inside each of your cells?◦ Tied around histones

Histones are proteins which act like thread spools. DNA is wound around the histones in order to fit inside a cell.

2) chromatin:◦ Strands are loose and

exposed ◦ Code for proteins

“recipes” can be read.

Why have 2 different forms of DNA in your cells?◦ The advantage of chromosomes is

_condensed genetic material can easily be moved to new cells during cell division.

◦ The advantage of chromatin is __loose genetic material can be ‘read’ because the DNA code is exposed.

Each one of your body cells has an exact copy of DNA.

That includes toe cells and nose cells, ear cells and eye cells!

Gene: _a segment of DNA that codes for the production of a protein.

Every species of eukaryotic organisms have a specific number of chromosomes in each cell: Organism Number of

Chromosomes in each cell.

Why are these numbers so different?

goldfish 94

chicken 78

horse 64 1) ____chromosomes come in different sizes__

sand dollar 52

chimpanzee 48 2) __different organisms have different numbers of genes_

dog 48

human 46

brown bat 44

corn plant 20

housefly 12

fruit fly 8

Gene: 1) A unit of hereditary information which can

be passed on to future generations. 2) A segment of DNA on a chromosome

which holds the code or ‘recipe’ for a protein.

3) Genes hold the code for synthesis of ◦ proteins : a functional group of many amino

acids

◦ Polypeptides: a smaller, non-functional group of amino acids (part of a protein)

◦ traits or parts of a trait : physical, behavioral and physiological traits

Eye Color

Hair Color

Review of the amino acid structure of proteins: Circle the R groups to identify individual aa’s.

How many different KINDS OF amino acids could be used to form a single protein or polypeptide? __20, one for each R group

Which group of organic compounds does DNA belong to? nucleic acids

Considering that DNA is a long molecule that must periodically be copied, it must be composed of simple units that fit together easily.

DNA is made of repeating subunits called nucleotides.   Each nucleotide is made up of 3 parts:

◦ a)_sugar______________◦ b) __phosphate group (PO4)◦ c) _nitrogen base_____

The sugar, __deoxyribose__and the phosphate groups are identical in all DNA nucleotides but there are four different types of nitrogen bases:◦ __adenine (A)_________________ ◦ __guanine (G)________________ ◦ __thymine (T)_______________◦ ___cytosine (C)______________

1) Deoxyribose Sugar (ribose sugar minus

an oxygen molecule)

vs. Ribose Sugar (found in RNA)

2) Phosphoric Acid

3) One of four different nitrogen bases:

PURINES◦ Adenine:

◦ Guanine:

PYRIMIDINES◦ Thymine:

◦ Cytosine:

Here is an example of an adenine nucleotide:

As you can see, the chemical structure of a nucleotide is difficult to draw so we normally draw a nucleotide using symbols/letters to represent the parts.

In the diagram above, what does the "A" stand for?____adenine___

What other letters could be used in that position? T, C, G

In the diagram above, what does the "S" stand for?_sugar_

In the diagram above, what does the "P" stand for? phosphate group

  How many different types of nitrogen bases are

there in DNA? ___4________

Name them:___adenine, thymine, guanine, cytosine_

  If each nucleotide contains _one__ nitrogen base. How many different types of DNA nucleotides can

be formed? _four

NOTE: Another type of nucleotide, Uracil, will replace the Thymine nucleotide in RNA molecules.

The drawing below is a MODEL representing a short piece of a DNA molecule. The key identifies phosphates, sugar and nitrogen bases.

The bonds that hold the molecules together in DNA are strong, covalent bonds.

The bonds holding the nitrogen bases are NOT covalent but are weak, hydrogen bonds.

Circle a nucleotide on the drawing above.

Circle a nucleotide on the drawing above.

What does each nucleotide have in common? ___sugar, PO4__

How do nucleotides differ from each other? ____different nitrogen base_

Notice that each nucleotide bonds with a nucleotide above and below it. This forms a strand of DNA.

How many strands make up a molecule of DNA? 2

The two strands are then twisted into a spiral shape, double stranded structure called a double helix.

Look at the model of DNA on the previous page. Use a red, blue, yellow and green colored pencil and follow the directions to answer the questions:

Look at drawing A. Circle a nucleotide on the right hand side or strand of the DNA molecule. What three parts can you identify?

1. ___sugar 2. __phosphate (PO4) 3. __nitrogen base__

List the names of the different bases: __A= adenine, G= guanine, C= cytosine, T= thymine__ Color the circled nucleotide. Color sugar red and the phosphate blue.

What is the name of the nitrogen base that you have circled?

Color the bases as follows: adenine and guanine-yellow, cytosine and thymine-green.

Circle another nucleotide on the left hand strand of the DNA molecule. Color the sugar, phosphorous and nitrogen base as above.

Imagine that the molecule of DNA in drawing A looks like a ladder. What two molecules make up the sides of the ladder? ___sugar__ and ___phosphate group

What two molecules make up the rungs of the ladder? (Rungs are where you place your feet.) ____one nitrogen base_ and a second, complimentary nitrogen base_

Color the remainder of the DNA molecule in drawing A according to the directions.

At what point are the right and left strands of DNA nucleotides joined?_between nitrogen bases

Is there any order to the pairing of the nitrogen bases down the center of the DNA molecule?◦ adenine is hydrogen bonded to thymine◦ cytosine is hydrogen bonded to guanine

Is this a pairing of purines with pyrimidines? ___purine is bonded with pyrimidine_______

Is there any order to the nucleotides down the right hand strand of the DNA molecule?

__no__ Is there any order to the nucleotides down

the left hand strand of the molecule? ___no____

In a molecule of DNA, adenine is always paired with __thymine T___

In a molecule of DNA, guanine is always paired with ___cytosine C_

In a molecule of DNA, a purine is always paired with a ___pyrimidine

We call this system of base pairing __complimentary base pairing___

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?

A-T-G-C-C-A-G-T-T Describe the shape of the DNA molecule in drawing B. twisted

ladder We call this twisted, double strand shape a ___double helix___

A segment of DNA is composed of 100 base pairs. If 25 of the nitrogen bases are adenine, how many are thymine?

a. 15 b. 20 c. 25 d. 30 e. 35

Human DNA contains about 10% cytosine. What percent of the bases are thymine?

a. 10% b. 20% c. 40% d. 80% e. 90%

Chromosomes can be seen in a single or double-arm, replicated form

Two configurations of chromosomes:

1) Single arm chromosomes are composed of a single chromatid.

  2) Double-arm chromosomes are

made up of paired, genetically identical chromati called sister chromatids. Sister chromatids are joined at the centromere. Because sister chromatids are formed during replication of DNA, they are identical right down to the nucleotide sequences!

Eye Color

Hair Color

Complete the blanks showing the "central dogma" of molecular biology.

DNA --> _____________ --> ______________ --> _______________

What process is illustrated by the arrow below?

A: DNA duplication B: DNA diploidy C: DNA replication D: DNA mutation

James Watson and Frances Crick (1953):along with Maurice Wilkins, were awarded the Nobel Prize for determining the structure of DNA.

Rosalind Franklin (1951):Expert in X-ray Crystallography, her work was used by Watson to determine the structure. Died before the prize was given out—cannot be awarded posthumously.

Genome :The entire set of genes that make 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. During the early years of the HGP, the Welcome Trust (U.K.) became a major partner; additional contributions came from Japan, France, Germany, China, and others. Project goals were to:

identify all the approximately 20,000-25,000 genes in human DNA, determine the sequences of the 3 billion chemical base pairs that

make up human DNA, store this information in databases, improve tools for data analysis, transfer related technologies to the private sector, and address the ethical, legal, and social issues (ELSI) that may arise

from the project. (Source: http://www.ornl.gov/sci/techresources/Human_Genome/home.shtml)

DNA unwinds and unzips from the enzyme DNA helicase.

DNA polymerase helps to link free floating DNA nucleotides between complimentary nucleotides.

Covalent Bonds Join nucleotides on the SAME strand and Hydrogen Bonds between opposite strands.

Each new DNA strand formed contains the SAME sequence of nucleotides.