Download From DNA to Proteins

FROM DNA TO PROTEINS
Chapter 8
KEY CONCEPT 8.1
DNA was identified as the genetic
material through a series of experiments.
GRIFFITH FINDS A ‘TRANSFORMING PRINCIPLE’
(GENETIC MATERIAL). 1928
•Griffith experimented with the bacteria that
cause pneumonia and discovered
transformation – when genetic material is
passed from one bacteria to another
•He used two forms: the S form (deadly) and
the R form (not deadly).
•A transforming material passed from dead S
bacteria to live R bacteria, making them
deadly.
AVERY IDENTIFIED DNA AS THE GENETIC MATERIAL.
•1944 DNAase, an enzyme that breaks down DNA,
prevents transformation.
•Therefore, DNA must be the genetic material
– Tests showed DNA was present.
– Enzyme tests showed only DNA-degrading
enzymes stopped transformation.
HERSHEY AND CHASE CONFIRM THAT DNA IS THE GENETIC
MATERIAL. 1952
Hershey and Chase studied viruses that infect
bacteria, or bacteriophages.
They tagged viral DNA with
radioactive phosphorus.
– They tagged viral proteins with
radioactive sulfur.
–
*Tagged DNA was found inside the bacteria; tagged
proteins were not. Therefore DNA is genetic material.
ROSALIND FRANKLIN AND MAURICE WILKINS
•Franklin’s x-ray images suggested that DNA
was a double helix of even width and that
molecules are spaced at regular intervals
•X- shape in crystallography image
X-Ray Diffraction Image of DNA
EDWARD CHARGAFF (1950)
•Number of adenine molecules = the number
of thymine molecules (A=T)
•Number of guanine molecules = number of
cytosine molecules (C=G)
Chargaff's Rules Erwin Chargaff showed that the
percentages of guanine and cytosine in DNA are almost
equal. The same is true for adenine and thymine.
WATSON AND CRICK DETERMINED THE THREEDIMENSIONAL STRUCTURE OF DNA BY BUILDING MODELS.
1953
•Building blocks of DNA
are nucleotides
•DNA is a double helix
(twisted ladder)
•Composed of a sugarphosphate backbone on
the outside with bases on
the inside.
KEY CONCEPT 8.2
DNA structure is the same in all
organisms.
DNA
Recall that:
•DNA controls cell functions and inheritance of traits
•Forms chromosomes in the nucleus
•DNA is wrapped around proteins, called histones
DNA IS COMPOSED OF FOUR TYPES OF
NUCLEOTIDES.
DNA is made up of a long chain of nucleotides.
Each nucleotide has three parts.
a phosphate group
a deoxyribose sugar
a nitrogen-containing base
phosphate group
deoxyribose (sugar)
nitrogen-containing
base
• The nitrogen containing bases are the only
difference in the four nucleotides.
PURINES AND PYRIMIDINES:
Purines- Adenine and Guanine are double rings,
formed from a 5 carbon ring fused to a 6 carbon
ring (both contain nitrogen)
Pyrimidines - Thymine and Cytosine made of a
single ring of carbon and nitrogen
NUCLEOTIDES ALWAYS PAIR IN THE SAME WAY.
The base-pairing rules show how
nucleotides always pair up in DNA.
– A pairs with T
– C pairs with G
G
A
C
T
• Because a pyrimidine (single ring) pairs with a
purine (double ring), the helix has a uniform width.
• The backbone is connected by covalent bonds.
• The bases are connected by weak hydrogen bonds.
hydrogen bond
covalent bond
•Aand T always pair together with 2 hydrogen
bonds.
•G and C pair with 3 hydrogen bonds.
•The two sugar-phosphate backbones run in
opposite directions (antiparallel)
KEY CONCEPT 8.3
DNA replication copies the genetic
information of a cell.
REPLICATION COPIES THE GENETIC INFORMATION.
•A single strand of DNA serves as a template for a new
strand.
•The rules of base pairing direct
replication.
•DNA is replicated during the
S (synthesis) stage of the cell cycle.
•Each body cell gets a
complete set of identical DNA.
PROTEINS CARRY OUT THE PROCESS OF REPLICATION.
•DNA serves only as a template.
•Enzymes and other proteins do the actual work of
replication.
•Enzymes unzip the double helix.
•Free-floating nucleotides form hydrogen bonds
with the template strand.
ANTIPARALLEL STRANDS
•The end with the phosphate group attached to the
ending sugar is called the 5’ end
•The 3’ end has an OH group attached to the #3
carbon on the sugar
•DNA polymerase only attaches to an OH group 3’,
thus replication proceeds from 3’ toward 5’ end along
the original strand; the new strand forms 5’ to 3’
STEPS OF REPLICATION:
1. DNA unzips with the help of helicase.
2. Helicases break hydrogen bonds between base
pairs forming a replication fork.
nucleotide
The DNA molecule unzips
in both directions.
STEPS OF REPLICATION (CONTINUED):
3. DNA polymerase forms a new complementary
strand for each old strand by adding nucleotides.
•Covalent bonds form between the nucleotides.
ex: Old Strand: A G G G G C G A C
New Strand:
new strand
nucleotide
DNA polymerase
Steps of Replication (Continued):
4. DNA polymerase also proofreads the strands to
ensure accuracy.
5. Two new molecules of DNA are formed, each
with an original strand and a newly formed
strand.
original strand
Two molecules of DNA
new strand
REPLICATION IS FAST AND ACCURATE.
• DNA replication starts at many points in
eukaryotic chromosomes.
• DNA polymerases can find and correct errors.
There are many origins of replication in eukaryotic chromosomes.
KEY CONCEPT 8.4
Transcription converts a gene into a
single-stranded RNA molecule.
CENTRAL DOGMA:
DNA
mRNA
PROTEIN
The central dogma states that information flows in one
direction from DNA to RNA to proteins.
RNA - RIBONUCLEIC ACID
1. RIBOSE is the sugar
2. Uracil (another pyrimidine) replaces thymine
3. Single strand
4. 3 types of RNA
Types of RNA Function
Messenger RNA
(mRNA)
carries the message that will be
translated to form a protein.
Transfer RNA
(tRNA)
brings amino acids from the
cytoplasm to a ribosome.
Ribosomal RNA
(rRNA)
forms part of ribosomes where
proteins are made.
DIFFERENCES BETWEEN DNA AND RNA:
DNA
RNA
1. thymine
1. Uracil
2. double
strand
2. single strand
3. deoxyribose
3. ribose
4. found in the
nucleus
4. in entire cell
5. larger
5. smaller
6. unzips and
replicates
6. forms off of DNA
PROTEIN SYNTHESIS OVERVIEW:
ONLINE ACTIVITY
What is a protein?
http://learn.genetics.utah.edu/units/basics/transcribe/
Step 1: Transcription
1. RNA polymerase and other proteins form a
transcription complex, which recognizes the start of a
gene and unwinds a segment of it.
2. Transcription: RNA polymerase makes
complementary copy of a section of DNA, forming
single-stranded mRNA
3. mRNA is edited and goes to ribosome
ex: DNA strand: A A T T G G C C C
mRNA copy:
UUA ACC GGG
Transcription:
transcription complex
start site
nucleotides
DNA
RNA polymerase
moves along the DNA
RNA
THE TRANSCRIPTION PROCESS IS SIMILAR TO REPLICATION:
Similarity: Transcription and replication both involve complex
enzymes and complementary base pairing.
Differences:
Replication copies
all the DNA; transcription copies a gene.
Replication makes one copy;
transcription can make many copies.
one
gen
e
growing RNA strands
DNA