DNA – The Code of Life
Chapter 12
DNA – deoxyribonucleic acid
Functions of DNA:
1. to store and use information to direct the
activity’s of the cell
2. to copy itself exactly in order to form new
cells
3. must be able to pass copies of their DNA
to offspring in order to keep species from
going extinct
DNA Nucleotides
 Made of 3 parts:
1. phosphate molecule
2. sugar molecule – deoxyribose
3. nitrogen base – can be 1 of the 4 below:
- adenine
- thymine
- cytosine
- guanine
**sugar & phosphate molecules are
ALWAYS THE SAME IN EVERY NUCLEOTIDE
DNA Nucleotides
Section 12-1
Adenine
Guanine
Cytosine
Go to
Section:
Phosphate
group
Thymine
Deoxyribose
Double Helix
(Watson & Crick Model)
 DNA molecule made of
- 2 strands of nucleotides held by hydrogen bonds
- looks like a twisted ladder
 Sides of ladder = sugars & phosphates
 Steps of ladder = pairs of nitrogen bases
Section 12-1
Structure of DNA
Nucleotide
Hydrogen
bonds
Sugar-phosphate
backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Go to
Section:
Guanine (G)
Complementary Pairs
 Each base of DNA has a complementary pair:
ADENINE BONDS WITH THYMINE
A–T
CYTOSINE BONDS WITH GUANINE
C–G
 Sequence of pairs are inherited by parents
 Holds all info to determine the structure & function of an
organism
- color of hair, eyes, & skin
- whether you are short or tall; if you are athletic or
musically talented
Warm up 4-24
1. What makes up a nucleotide?
2. List the functions of DNA?
3. Name the 4 nitrogen bases and pair
them up with their complementary pair.
4. Use the following sequence of bases to
construct a DNA molecule:
ATCGGCCTT
Structure of DNA Quiz
1. What is a nucleotide?
2. Name the 4 nitrogen bases and show which
3.
4.
5.
6.
ones are always paired together?
How many hydrogen bonds are between
each pair of nitrogen bases?
What is the name of the sugar found in
DNA?
What does DNA stand for?
Construct a DNA molecule using the
sequence below…
ACCGTTAAGGATCGA
Replication of DNA
 The process of making new DNA strands from an existing one
ORIGINAL DNA
A-T
T-A
C-G
C-G
G-C
T-A
UNZIPS

ORIGINAL
ATCCGT-
-T
-A
-G
-G
-C
-A
A-T
T-A
C-G
  C-G
G-C
T-A
NEW
A-T
T-A
C-G
C-G
G-C
T-A
Process of Replication
1. DNA Helicase (enzyme) attaches to DNA
2. Helicase “unzips” the 2 strands
- breaking the hydrogen bonds
3. Freely floating nitrogen bases bind with
exposed nitrogen bases
4. DNA Polymerase forms the bonds of the
newly formed strand & original strand
RESULT = 2 DNA Molecules – 1 NEW & 1 OLD
Replication
DNA Replication (continue)
 Sequence of nucleotides in each new strand
EXACTLY MATCH that of the original molecule
 Replication occurs simultaneously at many
points on the molecule
 Parts of DNA are copied at different times
 DNA molecule is never copied all at once
Accuracy & Repair
 Replication is very ACCURATE
 Cells have built-in “SPELL CHECK” to ensure
no errors with the matching of pairs
 Cells can also REPAIR itself
 Enzymes recognizes & removes damaged
nucleotides & replaces them with new ones
 This ensures accuracy of replication
Warm Up 4/25
 Turn to page 299 in text
 Answer questions 1-5
 Write out questions and answers on a
separate piece of paper
 Warm up due at 12:25
Discovering DNA Quiz
1. Which bases combine together in a DNA
2.
3.
4.
5.
molecule?
Define a nucleotide.
Where do the nucleotides come from
during DNA replication?
What are proteins made up of?
What organelle manufactures protein?
RNA – Ribonucleic acid
 DNA – stores & transports the info needed to
make proteins - instructions only
 RNA – uses the info (instructions) from DNA
to make the proteins
DNA vs. RNA
DNA
2 strands of nucleotides
Sugar = deoxyribose
Nitrogen bases:
Adenine-Thymine
Cytosine-Guanine
Instructions to make
proteins
RNA
1 strand of nucleotides
Sugar = ribose
Nitrogen bases:
Adenine-Uracil
Cytosine-Guanine
Uses instructions to
make proteins
Nucleotides of RNA
Each RNA nucleotide includes:
1. phosphate group
2. sugar molecule – Ribose
3. 1 of 4 nitrogen bases:
adenine
uracil
cytosine
guanine
Warm up 4-26
 Write Word of the Day in notebook
 Complete review worksheet – section 12-2
DNA vs. RNA Quiz 4-26
1. List 3 of the 4 differences between DNA
and RNA.
- you can answer using a table
- If you can list all 4 …..
- you will earn 5 extra credit points
Types of RNA – Concept Map
Section 12-3
RNA
can be
Messenger RNA
also called
which functions to
from
Go to
Section:
Ribosomal RNA
also called
to
which functions to
to make up
Transfer RNA
also called
which functions to
Types of RNA – Concept Map
Section 12-3
RNA
can be
Messenger RNA
also called
which functions to
mRNA
also called
which functions to
rRNA
Combine
with proteins
Carry instructions
from
nucleus
Go to
Section:
Ribosomal RNA
to
Rest of cell
to make up
Ribosomes
Transfer RNA
also called
which functions to
tRNA
Bring
amino acids to
ribosome
Transcription – when RNA is made from
DNA
DNA
RNA polymerase
separates DNA
A-T
C-G
T-A
G-C
A-T
A-T
A
C
T
G
A
A
T
G
A
C
T
T
RNA nucleotides
attach to DNA
A-U
C-G
T-A
G-C
A-U
A-U
New RNA
molecule is
made and
detaches
U
G
A
C
U
U
Transcription (cont.)
 All types of RNA are formed this way
 After RNA is made in the nucleus, it moves
into the cytoplasm
 In the cytoplasm, RNA is involved in the
synthesis (making) of proteins
Protein Synthesis
 3 mRNA nitrogen bases = CODON
 1 CODON = 1 AMINO ACID
example – AUC = isoleucine
 3 tRNA nitrogen bases = ANTICODON
- complementary pair to a CODON
example :
mRNA = AUC (codon)
tRNA = UAG (anticodon)


20 amino acids are made from 64 possible codons
This means that 1 amino acid can have more than one
codon that codes for it
THE GENETIC CODE
TRANSLATION
 assembling proteins from information encoded in mRNA.
 Process:
1. mRNA moves out of nucleus by passing through the nuclear
pores.
2. mRNA migrates to a group of ribosomes where tRNA
begins to “translate” the CODONS of mRNA and makes
ANTICODONS (complementary pair of a codon)
3. the ribosomes start to attach tRNA and amino acids together
4. the process continue until the POLYPEPTIDE (protein
molecule) is complete
Result = new POLYPEPTIDES are made
Begin with DNA >>> mRNA >>> end with tRNA
How Translation Works
DNA
A-T
G-C
A-T
use left side of
DNA to make
mRNA
A-U
G-C
A-U
mRNA
(codon)
U
C
U
tRNA
(anticodon)
A
G
A
(amino acid)
REMEMBER ONLY 1 SIDE OF DNA IS USED
TO START TRANSLATION
MUTATIONS
 Changes in the genetic material
 Occurs when:
1. cells make mistakes in copying
DNA.
2. inserting a wrong base
3. skipping a base as a new strand
is put together
Kinds of Mutations
 Gene Mutations – mutations of a single gene
1. Point Mutations – involve changes in 1 or
few nucleotides
- occur at a single point in the DNA sequence
A. Substitutions – one base is changed to
another
- affects only a single amino acid
DNA
mRNA
TAC GCA
DNA
AUG CGU >>>> mRNA
TAC
AUG
GTA
CAU
Amino acid
Met
Met
His
Arg
Amino acid
Gene Mutations (cont.)
2. Frameshift Mutations:
- shifts the “reading” frame of the genetic code
a. Insertion – adding an extra base
DNA
TAC GCA TGG AAT
mRNA
AUG CGU ACC UUA
Amino acids
Met – Arg – Thr – Leu
↓ Insertion
DNA
TAT CGC ATG GAA T
mRNA
AUA GCG UAC CUU A
Amino acid
Ile – Ala – Tyr – Leu
Gene Mutations (cont.)
b. Deletion: removing a base
THE
FAT
CAT
ATE
THE
RAT
If H is deleted in THE, the sentence would
read
TEF
ATC
ATA
TET
HER
AT
Gene Mutations (cont.)
 These mutations are more damaging than
point mutations
 They can alter a protein so much that it is
unable to perform its normal functions
Chromosomal Mutations
 Involve changes in the number or structure
of chromosomes
 Can change the location of genes on
chromosomes
 May even change the # of copies of some
genes
4 Types of Chromosomal Mutations
1. Deletion – loss of all or part of the
chromosome
2. Duplication – produces extra copies of
parts of a chromosome
3. Inversion – reverse the direction of parts
of chromosomes
4. Translocation – when part of one
chromosome breaks off
and attaches to another
Chromosomal Mutations
Original strand
ABC-DEF
Deletion
AC-DEF
Duplication
ABBC-DEF
Inversion
AED-CBF
Translocation
ABC-JKL
GH-JDEF
Figure 12–20 Chromosomal Mutations
Deletion
Duplication
Inversion
Translocation
Go to
Section:
Significance of Mutations
 Many mutations are NEUTRAL – cause little
or no damage to gene or proteins
 Few mutations can cause dramatic changes
that are very harmful and sometimes deadly
 However, mutations can also be very
beneficial, as a source of genetic variability
to allow a species to adapt to changing
environments
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
“Discovering DNA” Film
Questions
Which bases combine together in a DNA molecule?
Define a nucleotide.
What is a gene?
What is a genetic code?
Why are proteins so important in the functioning of a cell?
What are DNA polymerases?
Where do the nucleotides come from during DNA
replication?
What are proteins made up of?
What organelle manufactures proteins?
What is a codon?
What does mRNA stand for?
What are ribosomes made of?
What does tRNA do?
Where do you find tRNA?
List 6 places where DNA is found.
CODON BINGO
 Fill in your bingo card with the proteins
written on the board
 You need to use all of proteins on your
card
 You need to use 3 of the proteins TWICE
 When you are finished, open your books
to page 303
 You will use the “Genetic Code” dial to
help you with the game
Proteins for Codon Bingo
Alanine
Leucine
Glutamine
Lysine
Serine
Histitide
Glutamic acid
Arginine
Valine
Tyrosine
Glycine
Asparagine
Isoleucine
Methionine
Aspartic acid
Cysteine
Phenylalanine
Tryptophan
Proline
Theonine
Stop
THE GENETIC CODE
1. phosphate, deoxyribose, nitrogen base
2. Form organelles & control activities of the cell
3. A-T C-G
ADENINE THYMINE CYTOSINE GUANINE
4. ATCGGCCTTAATTCGTACGTA
TAGCCGGAATTAAGCATGCAT