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Chapter 12
•DNA structure
and replication
•RNA
•Transcription
•Translation
•Protein
synthesis
•Amino
acids
Discovery of the Genetic Material
• After the rediscovery of Mendel’s work,
scientist began to look for the molecule
involved in inheritance.
• For many years, scientists struggled to
determine if DNA or protein was the
source of genetic information.
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Discovery of the Genetic Material
Miescher
• 1860’s
• “nuclein”
Griffith
• First major experiment searching for the
genetic material
• Involved transformation between two forms
of S. pneumoni
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Chromosome Structure
• To fit into a cell, DNA coils around a group
of beadlike proteins
• Group together into chromatin fibers
• Supercoil to form a chromosome.
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DNA: The Genetic Material
Chromosome Structure
• Eukaryotes
– DNA in individual chromosomes
• Nucleus
• Prokaryotes
– DNA in Cytoplasm
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DNA: The Genetic Material
DNA
Structure
James Watson (L)
and Francis Crick
(R), and the model
they built of the
structure of DNA.
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DNA Structure
Double helix
• X-ray diffraction
techniques indicated
that DNA was a double
helix, or a twisted
ladder shape.
• Formed by two strands
of nucleotides twisted
around each other.
Copyright © McGraw-Hill Education
The structure of DNA and RNA
•Genetic
material of living organisms is
either DNA or RNA.
•DNA – Deoxyribonucleic acid
•RNA – Ribonucleic acid
•Genes are lengths of DNA that code for
particular proteins.
DNA and RNA are Polynucleotides
•Both
DNA and RNA are polynucleotides.
•Poly
= many
Nucleotide
are made
up of smaller molecules called
nucleotides.
•DNA is made of two polynucleotide strands:
•They
Nucleotide
Nucleotide
Nucleotide
Nucleotide
Nucleotide
Nucleotide
Nucleotide
Nucleotide
Nucleotide
Nucleotide
•RNA is
Nucleotide
made of a single polynucleotide strand:
Nucleotide
Nucleotide
Nucleotide
Nucleotide
DNA Structure
Nucleotides
• Nucleotides are the subunits of nucleic acids, and
consist of
• 5-carbon sugar
• Phosphate group
• Nitrogenous base
DNA Structure
• Pentose Sugar
– 5 carbon sugar
– DNA – deoxyribose
– RNA - ribose
DNA Structure
• Phosphate Group
– Link the sugar of one
nucleotide onto the
phosphate of the next
nucleotide to make a
polynucleotide.
DNA Structure
A Nitrogenous base:
• In DNA the
• Thymine
• Adenine
• Cytosine
• Guanine
four bases are:
• In RNA the
• Uracil
• Adenine
• Cytosine
• Guanine
four bases are:
AS Biology. Gnetic control of protein structure and function
Four DNA bases
•Four
kinds of nitrogenous bases:
•Purine bases
•Pyrimidine
bases
DNA: Complimentary base pairing
•Adenine
pairs with Thymine
A = T
Bond Type =
double
•Cytosine
pairs with Guanine
C = G
Bond Type =
Triple
DNA Structure
• DNA often is compared to a twisted ladder.
• Rails of the ladder are represented by the
alternating deoxyribose and phosphate.
• The pairs of bases (cytosine-guanine or thymineadenine) form the steps.
DNA STRUCTURE VIDEO
YUMMY GUMMY DNA
DNA Replication (in nucleus)
• Matching
bases allows DNA to be
easily copied
Making new DNA
•Replication
•Copying DNA
•DNA starts
as a double-stranded molecule
•matching bases (A:T, C:G)
•then it unzips…
DNA Replication
•Strands
bases
“unzip” at the weak bonds between
DNA Replication
DNA bases
in nucleus
•
Enzyme
• DNA polymerase
DNA
polymerase
• adds new bases
Copying DNA
 Build daughter DNA
strand
use original parent
strand as “template”
 add new matching
bases
 synthesis enzyme =
DNA polymerase

DNA
Polymerase
New copies of DNA
•Get
2 exact copies of DNA to split between
new cells
DNA
polymerase
DNA
polymerase
Copied & Paired Up Chromosomes
centromere
Comparing DNA Replication
• Eukaryotes and Prokaryotes
– Eukaryotic DNA unwinds in multiple areas as
DNA is replicated.
– In prokaryotes, the circular DNA strand is
opened at one origin of replication.
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Replication of DNA and
Chromosomes
Speed of DNA replication:
3,000 nucleotides/min in human
30,000 nucleotides/min in E.coli
Accuracy of DNA replication:
Very precise (1 error/1,000,000,000 nt)
AS Biology. Gnetic control of protein structure and function
3
Base your answer to the following question on the
diagram below which represents a portion of a doublestranded DNA molecule and on your knowledge of
biology.
The base sequence of strand II is most likely:
1. C-A-C-T-G-G
3. G-T-G-U-C-C
2. G-G-T-C-A-C
4. G-T-G-A-C-C
4
Practice
•On
your paper, complete the missing DNA
strand by adding the complementary bases.
•A T C G T T G C C A T C
•T A G C A A C G G T A G
DNA, RNA &
PROTEIN
Chapter 12: Section 3
Central Dogma
•Investigate
how DNA served as a genetic code
for the synthesis of proteins.
•Geneticists accept that the basic mechanism for
reading and expressing genes is from DNA to
RNA to protein.
•This is referred to as the central dogma of
biology:
•DNA codes for RNA, which guides the
synthesis of proteins.
Copyright © McGraw-Hill Education
RNA differs from DNA
1. RNA has a sugar ribose
DNA has a sugar deoxyribose
2. RNA contains uracil (U)
DNA has thymine (T)
3. RNA molecule is single-stranded
DNA is double-stranded
Central Dogma
Three Types of RNA
• Messenger
RNA (mRNA): long strands of RNA that
are formed complementary to one strand of DNA;
direct synthesis of a specific protein
• Ribosomal RNA (rRNA): associates with proteins to
form ribosomes in the cytoplasm
• Transfer RNA (tRNA): smaller segments of RNA
that transport amino acids to the ribosome
Copyright © McGraw-Hill Education
Central Dogma
Transcription
•First step synthesis of mRNA from DNA in a
process called transcription.
•RNA polymerase moves along the DNA strand
in a 3’ to 5’ direction, synthesizing mRNA.
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Practice
•Make
the complementary RNA strand for the
single strand of DNA below:
•A A T C A T C A C G T T
•U U A G U A G U G C A A
•Make
the complementary RNA strand for the
single strand of DNA below:
•T
A C C C G A G G T A G C C G C G T A T T
•A U G G G C U C C A U C G G C G C A U A A
Reading the genetic code
•The
genetic code is responsible for
building all the proteins in the body
using 20 different amino acids.
•How many 3 letter words can you
make from the letters A,T,G and C?
•Answer: 64
The Code
•Scientists hypothesized
that the instructions
from protein synthesis
were encoded in DNA.
•Experiments during the
1960s demonstrated
that the DNA code was
a three-base code.
•The three-base code in
DNA or mRNA is
called a codon.
Copyright © McGraw-Hill Education
DNA, RNA, and Protein
Codons
•A three
letter “word” that
specifies an amino acid.
A. Messenger RNA (mRNA)
start
codon
mRNA
A U G G G C U C C A U C G G C G C A U A A
codon 1
protein
codon 2
methionine
glycine
codon 3
serine
codon 4
isoleucine
codon 5
glycine
codon 6
alanine
codon 7
stop
codon
Primary structure of a protein
aa1
aa2
aa3
peptide bonds
aa4
aa5
aa6
The Code
Translation
• After synthesis, mRNA moves from the nucleus into the
cytoplasm, where it connects to a ribosome.
• The mRNA code is read and translated into a protein
through a process called translation.
Copyright © McGraw-Hill Education
DNA, RNA, and Protein
The Code
Translation
• tRNA molecules act as the interpreters of the mRNA codon
sequence.
• The tRNA is activated by an enzyme that attaches a specific amino
acid to the end.
• The middle of the folded tRNA contains an anticodon, a
complementary sequence to the mRNA codon.
Copyright © McGraw-Hill Education
DNA, RNA, and Protein
The Code
The role of the ribosome
• Ribosomes provide a site for protein synthesis.
• When mRNA leaves the nucleus, the two ribosomal
subunits come together to hold the mRNA in place for
translation.
• The ribosome structure has grooves that hold the mRNA
and serve as tRNA sites for amino acid attachment.
Copyright © McGraw-Hill Education
From DNA to Protein
DIFFERENCES
DNA
RNA
• Deoxyribonucleic acid
• Ribonucleic acid
• Double strand
• Single strand
• G, C, A, T
• G, C, A, U
deoxyribose sugar
• Inheritance of traits & enzyme
production
• ribose sugar
•
• protein synthesis
SIMILARITIES
NUCLEIC ACIDS
C, G, A
found inside the nucleus
If the cell is a school…
•The Nucleus is the school office
•The Nucleolus is the principal’s
office
•The DNA is the principal
•Ribosomes are the cafeteria
ladies
•mRNA is the email from the
principal to the cafeteria lady
Review/Explain:
Types of Nucleic Acids
What are the two types of nucleic acids?
Ribonucleic Acid (RNA)
• Single Stranded
Deoxyribonucleic Acid (DNA)
• Double Helix
• (Twisted
Ladder)
DNA
• Deoxyribose
• Base
Sugar
Pairs
A-T
G-C
• Phosphate
• Most Importantly--• Contains the Code for ALL the
Proteins in the Body
RNA
•
•
•
•
Ribonucleic Acid
Sugar + Phosphate
backbone
Differs from DNA
• Single Stranded
• Ribose Sugar
• Base Pairs A-U, G-C
RNA assists DNA in
manufacturing needed
proteins
Questions
•Name
one difference between DNA and
RNA.
•DNA – Double Helix, RNA – Single
Stranded
•DNA --- A-T, RNA ---A-U
•DNA ---Deoxyribose Sugar, RNA--Ribose
•What is a similarity of DNA and RNA?
•G binds with C in both DNA and RNA
•Both have sugar and phosphate backbone
Gel Electrophoresis
•use to separate DNA
fragments
• determine
relationships
• used in forensics
Study the diagram on
the left side of this
slide.
Which of the following
DNA samples of
individuals are most
closely related?
EXPLAIN.
DNA sample 1 & 7
Crime Scene #1
Crime
Scene
#2
Crime Scene
#3
Paternity
Paternity
#1
Dad 2
Paternity #2
WHO ARE THE PARENTS?
WHO ARE THE PARENTS?
Child 1
Child 2
Child 3
Child 4
Mom and Dad
Mom
Mom and Dad
Neither