Download 8From DNA to Proteins

8
CHAPTER
From DNA
to Proteins
Getting Ready to Learn
Preview Key Concepts
8.1 Identifying DNA as the Genetic Material
DNA was identified as the genetic material through a series of experiments.
8.2 Structure of DNA
DNA structure is the same in all organisms.
8.3 DNA Replication
DNA replication copies the genetic information of a cell.
8.4 Transcription
Transcription converts a gene into a single-stranded RNA molecule.
8.5 Translation
Translation converts an mRNA message into a polypeptide, or protein.
8.6 Gene Expression and Regulation
Gene expression is carefully regulated in both prokaryotic and
eukaryotic cells.
8.7 Mutations
Mutations are changes in DNA that may or may not affect phenotype.
Review Academic Vocabulary
Write the correct word for each definition.
enzyme ribosome protein
1.
: biological catalyst
2.
: site of protein synthesis
3.
: shape determines its function
Preview Biology Vocabulary
See how many key terms from this chapter you already know. Rewrite
each phrase, using a different word or words for the words in bold.
Phrase
Rewritten with Different Words
1. DNA replication allows every new
cell to have a complete set of DNA.
DNA
allows every
new cell to have a complete set of DNA.
2. Mutagens such as UV light can result
in skin cancer.
3. RNA is found in both the nucleus
and the cytoplasm.
such as UV light
can result in skin cancer.
is found
in both the nucleus and the cytoplasm.
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section
8.1
Identifying DNA as the
Genetic Material
> Virginia standards
BIO.1 The student will demonstrate
an understanding of scientific
reasoning, logic, and the nature of
science by planning and conducting
investigations.
BIO.1.EKS-23; BIO.5.EKS-11
Key Concept DNA was identified as the genetic material through a series
of experiments.
DNA was identified as the genetic material relatively recently—in the
1950s. This section reviews three research projects that all added up to
this discovery: 1) Griffith’s research, 2) Avery’s research, and 3) Hershey
and Chase’s research. Together, these scientists’ findings led to the conclusion that DNA is the genetic material.
Griffith finds a “transforming principle.”
In 1928 a British microbiologist named Frederick
Griffith investigated two forms of the bacterium that
causes pneumonia*. He injected the two different forms
into mice. One form of the bacterium killed the mice,
but the other form did not.
Griffith used heat to kill a sample of the deadly
disease-causing bacteria and then mixed the dead
bacteria with a sample of live, harmless bacteria. He
injected this mixture into mice. Even though the
disease-causing bacteria that he injected were heatkilled, the mice still died.
Griffith concluded that some material must have
been transferred from the heat-killed bacteria to the
live
harmless bacteria. Whatever that material
was, itlive
conS bacteria
bacteria
tained information that changed the harmlessRbacteria
into disease-causing bacteria. Griffith called this mystery material the “transforming principle.”
Griffith’s Experiments
The S form of the bacterium is deadly;
the R form is not.
livelive
S bacteria
S bacteria
livelive
R bacteria
R bacteria
heat-killed
heat-killed
S bacteria
S bacteria
heat-killed
heat-killed
S bacteria
S bacteria
+ live
+ live
R bacteria
R bacteria
dead
dead
mouse
mouse
livelive
mouse
mouse
livelive
mouse
mouse
dead
dead
mouse
mouse
heat-killed
S bacteria
heat-killed S bacteria
+ live R bacteria
live mouse
dead mouse
Transform means “to change.” Why do you
think Griffith called the mystery material the
“transforming principle”?
dead mouse
live mouse
* Academic Vocabulary
pneumonia a disease that affects the lungs
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Avery identifies DNA as the transforming
principle.
Oswald Avery worked with other biologists for over ten years trying to
figure out what Griffith’s transforming principle was. They thought the
transforming principle could be protein or it could be DNA. Avery’s
group found a way to separate this mystery material from samples of
bacteria. They ran several tests on the material. Their tests and findings
are shown in the chart below.
Avery’s Research
TEST
RESULT
1. Standard chemical test for protein
and DNA
found presence of DNA, but no protein
2. Tests to determine the amounts of
nitrogen (N) and phosphorous (P)
the proportions of N and P matched the
makeup of DNA, but not protein
3. Tests to see which enzymes could
break down the substance
enzymes that break down DNA broke down
this substance, but enzymes that break down
protein did not break down the substance
Avery and his group concluded that DNA must be the transforming
principle, or genetic material. Some scientists questioned this conclusion. Scientists also wondered whether DNA was the genetic material for
all organisms or just for bacteria.
On the chart above, highlight three reasons Avery concluded
that the mystery material was DNA, not protein.
Hershey and Chase confirm that DNA is the
genetic material.
In 1952 the work of Alfred Hershey and Martha Chase provided evidence that DNA is indeed the genetic material. Hershey and Chase
studied a type of virus that infects bacteria, called a bacteriophage
(bak-TEER-ee-uh-fayj), or “phage” for short.
A phage infects a bacterium by inserting its genetic material into the
bacterium. Hershey and Chase wanted to find out what material the
phage inserted into a bacterium—was it protein or was it DNA? They
conducted two experiments. In the first experiment, Hershey and Chase
marked the phages’ proteins with radioactive labels. When the phages
infected the bacteria, no significant radioactivity was found inside the
bacteria. In the second experiment, Hershey and Chase marked the
phages’ DNA with radioactive labels. When the phages infected the
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DNA
protein
coat
Bacteriophages are
viruses that infect
bacteria.
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bacteria, high levels of radioactivity were found inside the bacteria. These
results finally convinced scientists that the genetic material is DNA and
not protein.
What is the material that phages insert into bacteria?
8.1 Vocabulary Check
bacteriophage
Mark It Up
Go back and highlight
each sentence that
has a vocabulary
word in bold.
1. How did Hershey and Chase’s research with bacteriophages help confirm that DNA is the genetic material?
8.1 The Big Picture
2. Complete the following chart about the three main research projects
that led to the identification of DNA as the genetic material.
Researchers’ names
Summary of research
Griffith
Summary of Conclusions
found a “transforming principle”
Avery
Hershey and Chase
identified the substance that phages inject
into bacteria
3. Which of the three experiments gave evidence that protein was not
the genetic material?
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section
8.2
> Structure of DNA
Virginia standards
BIO.5.e The student will investigate
and understand common mechanisms
of inheritance and protein synthesis.
Key concepts include historical
development of the structural model
of DNA.
BIO.1.EKS-23; BIO.5.EKS-11;
BIO.5.EKS-12
Key Concept DNA structure is the same in all organisms.
DNA is composed of four types of nucleotides.
VISUAL VOCAB
Since the 1920s scientists have known the chemical parts of
the DNA molecule. DNA is a very long polymer, or chain of
repeating units. The units, or monomers, that make up DNA
are called nucleotides (NOO-klee-oh-tydz).
Each nucleotide
N
NH
2
HC N
has three parts: a phosphate
a base, and a sugar.
N C group,
2
HC N
CNH
NH2
C
HC
HN
NH2 of DNA nucleotides:
C CN
HC
A
There are four different
cytoHN C C types
C
CN
AA
HN C
HN adenine
C N CH N (A), and guanine
sine (C), thymine (T),
(G).
All
of
A
CN
CH N
N
CH
the nucleotides contain aN phosphate
group and a deoxyribose
CH
sugar. They differ in their nitrogen-containing bases, as
shown in the table below.
Notice that thymine (T) and cytosine (C) have nitrogenN
O
containing bases with
structure. Adenine (A)
HC aNsingle-ring
N C CO
HC N
O
and guanine (G) areHC
HC
C withO a double-ring structure.
HNbases
C CC CC NH
G
CDNA is madeGof billions
A single molecule ofHN
human
HN C
HN C N C NH
G
NH
CN
G
of nucleotides.
C NH
The small units, or monomers, that
make up a strand of DNA are called
nucleotides. Nucleotides have
three parts.
phosphate group
nitrogen-containing
base
deoxyribose (sugar)
•phosphate group: one phosphorus
with four oxygens
•deoxyribose: ring-shaped sugar
•nitrogen-containing base: a single
or double ring built around nitrogen
atoms and carbon atoms
N
N
C NH2
CNH2
NH
NH22
The Four Nitrogen-Containing Bases of
DNA
PYRIMIDINES = SINGLE RING
Name of Base
thymine
cytosine
Structural Formula
O
CH3
CH3
CH3
CH3
O
OC
OC
C C
C C
CHC
C
HC
HC
HC
NH
NH
NH
NHC
C
NHC
NH C
NH
NH
NH2
NH2
NHC2
NH
C2 N
HC C N C
N
HC C N
HCHC NHCC
HC
HC NH C
HC NH
HC NH
CO
CO
CO
CO
Model
T
TT
T
N
NH2
HC N
C
HC
PURINES = DOUBLEHNRING C C NH2
C
N
HN C
Name of Base
Structural Formula
CN
N
CH
N CH
NN
NH2 2
NH
HC
HC
adenine
CC
C
C
HN
HN
CC
NN
NN CH
CH
guanine
O
O
O
O
C
CC
C
Circle the names of the four nucleotides shown
table above.
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N
HC
N
C
HC
C
HN
C
HN
C
N
N
NN
HC
HC
CC
HN
HN
C
C
in the
NN
A
Model A
AA
O
C O
C
NH
NH
G
G
NH
NH
GG
C
CNH2
NHO2O
CC
CC
NH22
NH
O
O
C NH
CH3 C C NH
C
CH3 C
HC NH C
HC NH
OO
CC NH
NH
CH3 3 CCNH2
CH
NH2 CC
C N
HCC NH
HC
NHN
HC
C
HC
HC NH C
HC NH
NH2
NH
CO
CO
T
T
CO
CO
TT
O
O
C
C
NN
CC OO
HC NH
HC
NH
CC
2
CC
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Watson and Crick developed an accurate* model
of DNA’s three-dimensional structure.
For a long time, scientists hypothesized that DNA in all organisms was
made up of equal amounts of the four nucleotides. Then Erwin Chargaff
found that the proportion of the bases differs from organism to organism. In the DNA of each organism, the amount of A equals the amount
of T, and the amount of C equals the amount of G.
Then in the early 1950s, the scientists Rosalind Franklin and Maurice
Wilkins used x-rays to make a kind of photograph of DNA molecules.
These photographs did not show what DNA looks like, but they showed
patterns that gave clues about DNA’s structure.
Around the same time, the scientists James Watson and
Francis Crick were working together to figure out DNA structure, too. Based on the work of other scientists, they hypothesized that DNA might have a spiral, or helix (HEE-lihks),
shape. Watson and Crick saw Franklin’s photos and used the
information to complete their model of DNA structure.
In April 1953 Watson and Crick published their DNA model
in a paper in the journal Nature. They found that nucleotides
fit together in a double helix. Two strands of DNA wrap
around each other like a twisted ladder.
What new information did Watson and Crick contribute to science?
Watson and Crick’s model showed
DNA in the shape of a double helix.
Nucleotides always pair in the same way.
Each side of the DNA double helix is a long strand of phosphates and
sugars, connected by covalent bonds. The two sides of the double helix
are held to each other by hydrogen bonds that form between the bases in
the middle. Each individual hydrogen bond is weak, but together they
are strong enough to hold the shape of DNA. The bases of the two DNA
strands always bond according to the base pairing rules: T pairs with A,
and C pairs with G.
The bases pair in this way because of hydrogen bonds. Notice that
A and T form two hydrogen bonds, whereas C and G form three.
To help remember the rules of base pairing, notice that the letters G
and C have a similar shape. Once you know that G and C pair together,
you know that A and T also pair together. If the sequence of bases on
one DNA strand is CTGA, the other DNA strand will be GACT.
* Academic Vocabulary
accurate correct
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Base Pairing Rules
The base pairing rules describe how nucleotides form pairs in
DNA. T always pairs with A, and G always pairs with C.
T
A
G
C
A
This ribbonlike part
represents the phosphate groups and
deoxyribose sugar molecules that make up
DNA’s “backbone.”
T
T
C
G
hydrogen bond
covalent bond
A
G
The nitrogen-containing bases bond
in the middle to
form the rungs of
the DNA ladder.
C
A
T
C
G
What sequence of bases would pair with GTACG?
8.2 Vocabulary Check
nucleotide
double helix
base pairing rules
Mark It Up
Go back and highlight
each sentence that
has a vocabulary
word in bold.
1. Label the drawing at the right with the terms nucleotide, base pairing
rules, and double helix. Write each term and draw a line that connects
the term to the appropriate part of the drawing.
8.2 D
D
C
P
D
T
D A
D
P
D
P
D
D
P
D
G
P
D
G
A
T
P
D
C
P
P
C
D
C
P
G
D
P
P
T
D
The Big Picture
P
A
D
A
P
2. What are the three different parts of a nucleotide?
D
D
D
P
C
P
D
P
P
G
P
P
D
T
D
3. What are the names of the four nucleotides?
G
P
C D
G
D
P
P
D
T
A
D
P
4. Use the base pairing rules to write the sequence that would pair with
the following sequence: TCACGTA
DG
P
D
D
P
D
C
P
D
C
P
G
D
P
T
128
A
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