NUCLEIC ACIDS

NUCLEIC ACIDS

Below is one of the molecules that makes up DNA. What functional groups do you see in the

molecule:

1. Hydroxyl2. Carboxyl3. Amino4. Phosphate

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

Functions of DNA

• Control the processes of heredity by which cells and organisms reproduce proteins

Types of Nucleic Acids

1. DNA (deoxyribonucleic acid): double-stranded

2. RNA (ribonucleic acid): single-stranded

Nucleic Acid Structure

• The monomer units of DNA are known as nucleotides

• All nucleotides have three “parts” in common: a. Phosphate “backbone”b. Pentose sugar (ribose or deoxyribose)c. Nitrogen base

Deoxyribose Sugar (DNA)

• Has 5 carbons and 3 oxygens• Carbon atoms are numbered 1', 2', 3', 4',

and 5' – Distinguishes from the numbering of the

atoms of the purine and pyrmidine rings• 5'-carbons link to the phosphate groups• 3'-carbons link to the hydroxyl groups

• Direction of the nucleotides in one strand is opposite to their direction in the other strand: the strands are antiparallel.

• Asymmetric ends of DNA strands are called the 5′ (five prime) and 3′ (three prime) ends– 5' end having a terminal phosphate group– 3' end having a terminal hydroxyl group

Nitrogen Bases• Weak hydrogen bonds connect

complementary nitrogen bases• Two types:

a. Pyrimidines: form hexagon shaped rings1. Cytosine2. Thymine (only DNA)3. Uracil (only RNA)

b. Purines: combination of a pentagon shaped ring and a hexagon shaped ring

1. Adenine2. Guanine

Nitrogen Base Pairing

• Adenine and Thymine must form two hydrogen bonds to be stable while Guanine and Cytosine must form three– Makes the base pairing system an extremely

simple: the A-T and C-G pairs are the only ones physically possible

Let’s Practice How to Form DNA!

We will use our hands to represent a nucleotide.

SUGAR

PHOSPHATE NITROGEN BASE

The four different Nitrogen Bases for DNA are abbreviated using the following letters….

Adenine

Thymine

Guanine

Cytosine

A

T

G

C

Using your two hands, please show how you think two nucleotides will/should bond together.

Did you put your hands like this???

Time to find out why this is wrong!!!

Adenine and Guanine are larger molecules known as…

PURINES

LOOK! TWO RINGS!!!

THYMINE and CYTOSINE are smaller molecules known as…

PYRIMIDINES

LOOK! Only one ring!!

Now, when using our hands to represent the nucleotides, we must modify the nitrogen base in order to represent these PURINES and PYRIMIDINES.

How would you represent a large PURINE?

How would you represent a small PYRIMIDINE?

Full Finger

Half Finger

In DNA, a PURINE always bonds with a PYRIMIDINE when forming a “rung” of the DNA ladder.

LOOK! A long finger pairs with a short finger! In other words, a purine pairs with a pyrimidine.

In DNA, Adenine always pairs with Thymine using two hydrogen

bonds.

A T

In DNA GUANINE always pairs with CYTOSINE using three hydrogen bonds.

G C

Time to use your brain and hands in order to review nucleotide structure and type.

USING YOUR HAND, SHOW ME THYMINE

USING YOUR HAND SHOW ME ADENINE

SHOW ME CYTOSINE

SHOW ME HOW CYTOSINE AND THYMINE BOND TO FORM A RUNG ON THE LADDER

THEY DON’T

OK

Now that you recognize nucleotide type and structure, it’s time to start building the polymer

from these monomers.

The molecules marked “W” are best described as:

1. Monomers2. Polymers3. Isomers4. isotopes

Reactions A and B are respectively

known as:

A B

1. Dehydration, hydrolysis2. Condensation, hydrolysis3. Polymerization, decomposition4. Hydrolysis, dehydration

Molecule(s) “X” are most likely:

1. Carbohydrates2. Monomers3. Polymers4. Water5. Starch

If molecule “W” is a nucleotide, molecule marked “Y” is most likely:

1. Protein2. Starch3. DNA4. Galactose5. Fructose

In order to make a molecule of DNA, you would need to create many rungs to the DNA ladder.

Look. Many Rungs.

Etc…

What part of the nucleotide alternates to form the sides of the DNA ladder?

Etc…

Sugar, Phosphate.

Sugar, Phosphate.

Sugar, Phosphate.

Etc…

What makes up the “RUNGS” of the ladder?

The Nitrogen Bases

Go Ahead!Stack you hand on top of your partners hands building two rungs of the DNA ladder.

Why is this WRONG????

The sides of the DNA ladder “run” in opposite directions. One side is actually flipped and the nucleotides are upside down!

TRY IT!!!

Because the sides of the DNA “run” in opposite directions, DNA is said to be ANTIPARALLEL.

In this DNA molecule, the THUMB part or better known as the PHOSPHATE GROUP, is said to be the 5 prime (5’) end.

5 prime

5 prime

The “hand” or sugar part of the DNA molecule makes up the 3 prime (3’) end of the DNA ladder.

3 Prime

3 Prime

If you link enough nucleotides together, the DNA molecule begins to take on the characteristic shape known as the

Double Helix