DNA

What are nucleic acids?Why is DNA important?

Structure of DNAScientists

Review

• What are the two types of nucleic acids? _________________ & _______________

• Is a nucleic acid a monomer or polymer? __________________________

• What is the monomer of DNA and RNA? _________________________

DNA RNA

POLYMER

nucleotide

DNA Location• DNA stands for deoxyribonucleic acidLocation:• DNA is found in the nucleus of eukaryotic

organisms – like plants, animals, protists and fungi

• In prokaryotic organisms (like bacteria) that do not have a nucleus, DNA can be found in a single circular chromosome within the cell

DNA Function

Function: DNA stores and carries the information that is passed from one organism to its offspring (from parent to child)

What is DNA?• The information is coded in the order of

the nucleotide bases (the monomers)

• The monomer of DNA is made of:– Phosphate group– 5 carbon sugar (deoxyribose)– Nitrogen containing base

These three components make the monomer called a nucleotide

Nucleotide

Why is DNA Important?• DNA is in all living things • DNA is the informational code that

makes each organism unique.

The Structure of DNA• double helix- two strands of

nucleotides twisted around each other, like a winding staircase

• there is a “right side up” strand and an “upside down” strand.

• this arrangement of 2 strands running side by side but in opposite directions is described as antiparallel

The Structure of DNANucleotides- subunits (monomers) that make

up DNA composed of:– Phosphate group– 5- carbon sugar (deoxyribose in DNA)– Nitrogen containing base:

• The bases pair in the same way in every DNA molecule, we call this complementary base pairing

• Adenine Thymine (A – T)• Guanine Cytosine (G – C)

* Weak hydrogen bonds hold bases together

Base Pairs• We refer to adenine, thymine,

cytosine and guanine as the nitrogen bases or just “bases”

• So, when you say “a sugar, a phosphate and a base” you are implying that the base is either adenine, thymine, guanine or cytosine

Base PairsThe order of the base pairs provides that “unique code”

that makes us all different.

• GTAACTTAG does not contain the same information as GGACAATTT even though both sequences contain the same nucleotides

• However, if the nucleotide sequences of nitrogenous bases (adenine, guanine, cytosine, thymine) are in a similar order, the more related two organisms are closely related– This concept is used in forensic science and is called

DNA fingerprinting

Label complementary bases and draw the appropriate

number of hydrogen bonds

ACATGTAC

TGTACATG

The Structure of DNA*Note about bases:– Pyrimidines- single ring of carbon• Tymine and Cytosine

– Purine- two rings of carbon• Adenine and Guanine

A purine must always hydrogen bond with a pyrimidine!

A

C

Label:-Phosphate (P)

-5 carbon sugar (S)

- Correct base pairs(A, T, C, G)

-Label all hydrogen bonds with an H

-Label the 5’ and 3’ ends

Circle a nucleotide

A

T

G

A

P

P

P

P

P

PP

P

P

P

P

PS

S

S

S

S

S

S

S

S

S

S

S

T

T

G

A

T

C

H

H

H

H

H

H

3’

5’