Mrs. StewartBiology I Honors

DNAStructur

e

STANDARDS:CLE 3210.4.1 Investigate how

genetic information is encoded in nucleic acids.

CLE 3210.4.2 Describe the relationships among genes, chromosomes, proteins, and hereditary traits.

OBJECTIVES: (today, I will…)Evaluate the structure of nucleic

acids Determine how genetic information is

“coded” in nucleic acids Create complementary DNA strands

using Chargaff’s rule

Nucleic AcidsMacromolecules containing :

Carbon HydrogenOxygenNitrogenPhosphorus

Function: Store and transmit genetic/hereditary information

Two types of Nucleic Acids

DNARNA

DNA Stands for:

Deoxyribonucleic Acid

DNA StructureDNA is made up of two strands that are

arranged into a twisted, ladder-like structure called a Double Helix.

A strand of DNA is made up of millions of tiny subunits called Nucleotides.

Each nucleotide consists of 3 parts:1. Phosphate group2. sugar3. Nitrogenous base

Nucleotides

Phosphate

Pentose

Sugar

Nitrogenous

Base

DNA sugarThe 5 carbon sugar for DNA is

Deoxyribose

That is where the name (Deoxyribo)nucleic acid comes from

NucleotidesThe phosphate and sugar form the

backbone of the DNA molecule, whereas the bases form the “rungs”.

There are four types of nitrogenous bases.

4 different Nitrogen bases

A

Adenine

T

Thymine

G

Guanine

C

Cytosine

Purines

A

Adenine

G

Guanine

Pyrimidines

T

Thymine

C

Cytosine

Chargaff’s ruleErwin Chargaff observed that the

percentage of adenine equals the percentage of thymine, and the percentage of cytosine equals the percentage of guanine.

Example: in one strand of DNA the following amounts may be found:15% Adenine15% Thymine35% Cytosine35% Guanine

Complementary base pairing:Each base will only bond with one

other specific base. (Chargaff’s rule)

Adenine (A)Thymine (T)

Cytosine (C)Guanine (G)

Form a base pair.

Form a base pair.

DNA StructureBecause of this complementary base

pairing, the order of the bases in one strand determines the order of the bases in the other strand.

G

G

A

T

T

A

A

C

T

G

C

A

T

C

Practice:Complete the complementary DNA strand for

the following sequence:

G T A A C T C C TC A T A G A G G A

C T C C T A A A CG A G G A T T T G

T A G A A T G C CA T C T T A C G G

DNA StructureTo crack the genetic code found in

DNA we need to look at the sequence of bases.

The bases are arranged in triplets (sets of 3) called codons.

A G G - C T C - A A G - T C C - T A GT C C - G A G - T T C - A G G - A T C

DNA StructureA gene is a section of DNA that codes for a

protein.

Each unique gene has a unique sequence of bases.

This unique sequence of bases will code for the production of a unique protein.

It is these proteins and combination of proteins that give us a unique phenotype.

Protein

DNA

Gene

Trait

Your TaskDraw a flow chart to

show how to get from:

Mrs. StewartBiology I Honors

DNA Replicati

on

STANDARDS:CLE 3210.4.1 Investigate how

genetic information is encoded in nucleic acids.

CLE 3210.4.2 Describe the relationships among genes, chromosomes, proteins, and hereditary traits.

OBJECTIVES: (today, I will…)Evaluate the structure of DNA and

the need for replicationCreate complementary DNA strands

to simulate replication

DNA Double HelixMade of 2 strands of nucleotidesThese strands are joined together with the pairing of the Nitrogen bases(A, T, C, G)

The bases are joined by Hydrogen bonds

Think – Pair - ShareLook at the picture and try to figure

out what “antiparallel” means.

Did you notice that the strands of DNA run in “opposite directions”?

5’ and 3’ ends of DNARefers to the orientation

of the carbon atoms on the deoxyribose

Strands run in opposite directions

One strand is “upside down”

Think – pair - shareWhy does DNA need to replicate

itself?

DNA ReplicationDNA makes an exact copy of itselfOccurs during the S stage of

interphase

Semi-conservativeEach strand of the double

helix will serve as a template for the new strands that will form

End result is two complete DNA double helixes – each containing one strand from the original molecule and one newly made complementary strand

HelicaseEnzyme that “unzips”

the DNA double helix by breaking the Hydrogen bonds between the bases to separate the strands in preparation for replication

Creates a “replication fork”

DNA PolymeraseUses “free-floating” nucleotides in the nucleus to build the complementary strand of DNA

5‘ to 3‘ directionThe new DNA strands need to form in

the 5 prime to 3 prime direction.

Leading strand: forms continuously because it is forming in the 5’ to 3’ direction

Lagging strand: forms in short segments called Okazaki fragments, so that it can also form in the 5’ to 3’ direction

Animation of replication #1Animation of replication #2