Chapter 13 DNA, RNA, & Proteins
Chapter 13
DNA, RNA, & Proteins
DNA
Deoxyribonucleic acid (DNA) is the
material that contains the information
that determines inherited characteristics.
In other words, it contains our genes.
The History of DNA
3 major experiments lead to the
conclusion that DNA is the genetic
material in cells. These
experiments were performed by
Griffith, Avery, Hershey, and Chase.
Griffith – Experimented on mice and
observed some harmless strains of
bacteria could change into harmful
strains. He called this transformation.
His study led to the conclusion that
genetic material could be transferred
between cells.
Transformation- a change in genotype
that is caused when cells take up
foreign genetic material.
Avery – 1940- wanted to determine if
the transforming agent in Griffith’s
experiments was protein, DNA, or
RNA. Discovered that DNA is the
nucleic acid that is responsible for
transformation.
He did this by using enzymes to
destroy each agent (one at a time)
and observing if R cells were
transformed into S cells.
Hershey-Chase experiment
Studied bacteriophages (viruses that
infect bacterial cells & cause the cells to
produce viruses)
Found that the genetic material of viruses
was DNA, not proteins
DNA Structure
DNA is a relatively simple molecule that is
composed of a 5 carbon sugar (deoxyribose),
a phosphate group, and 4 different subunits
known as nitrogenous bases:
-Adenine (A) -Guanine (G)
-Thymine (T) -Cytosine (C)
Gene- a segment of DNA that is
located in a chromosome and that
codes for a specific hereditary trait.
Chargaff’s Rules for base pairing
•Adenine always binds to Thymine A---T
•Guanine always binds to Cytosine G---C
•When two nitrogenous bases are bound
together, they are known as a base pair.
•These paired bases are called complimentary
because they fit together like puzzle pieces.
Purine- a nitrogenous base that
has a double ring structure (A & G)
Pyrimidine-a nitrogenous base that
has a single ring structure (T & C)
Watson & Crick
Built the first 3-D model of DNA using the
information from Chargaff, Rosalind Franklin
(x-rayed a DNA molecule), & their own
knowledge of chemical bonding.
Watson & Crick won a Nobel prize for their
discovery.
DNA Replication
1. Proteins called helicases separate the 2
original DNA strands
2. Complimentary nucleotides are added to
each strand by DNA polymerase
3. Two DNA molecules are formed that are
identical to the original DNA molecule
DNA replication- the process of
making a copy of DNA
DNA helicase- an enzyme that
unwinds the DNA double helix
during DNA replication
DNA polymerase- an enzyme that
catalyzes the formation of the DNA
molecule
DNA replication in prokaryotes
(binary fission)
1. Original Site of Replication Fork
2. Each of the Two Strands of DNA separate from each other and synthesis of a complementary strand on each parental strand begins
3. Loop of DNA Extending Out of The Plane of the Parental Bacterial Chromosome
4. Rotation Around Axis
BR - Copy the diagram and the question. Then,
answer the question.
Which sequence of
bases do the question
marks represent?
SWP – trans-?
EQ – Why is RNA needed to make proteins?
C C T A T G ? ? ?
G G A T A C C T G
DNA Replication Practice
•TTG GAG CGT GCT
•GCA CAT TTA CGA
•AAC GGC CTG CAG
Ribonucleic acid
RNA
RNA- a nucleic acid that is
essential in taking the genetic
information from DNA and building
proteins
3 types:
messenger RNA (mRNA)
transfer RNA (tRNA)
ribosomal RNA (rRNA)
mRNA
When DNA is transcribed into RNA, mRNA
is the type of RNA made. mRNA is
complementary to the DNA sequence of a
gene. The mRNA carries the instructions for
making a protein from a gene and delivers
them to the site of translation.
tRNA
During translation, tRNA “reads” the mRNA
sequence (codons) and builds amino acids
from those codes
rRNA
ribosomal RNA- RNA component of
ribosomes. Provides a mechanism for
decoding mRNA into amino acids & interacts
with tRNA during translation.
RNA Stucture:
-a single strand version of DNA
-contains 4 nitrogenous bases
(A,U,C,G)
-Uracil instead of Thymine
-A binds to U
-G binds to C
Differences in RNA & DNA RNA- Single stranded
sugar is ribose
uracil instead of thyamine
located in the nucleus & cytoplasm
DNA- double stranded
sugar is deoxyribose
thyamine instead of uracil
located in the nucleus
Transcription- the information in a
specific region of DNA (a gene) is
copied into mRNA
3 steps:
1. Initiation- RNA polymerase binds to
a DNA sequence in the gene known as
the promoter (the start point)
2. Elongation- The two DNA strands
unwind and separate, exposing the
bases. Complementary RNA nucleotides
are added by RNA polymerase, growing a
strand of mRNA.
3. Termination- The RNA polymerase
eventually reaches a ‘stop’ code at the
end of a set of genes. The mRNA
strand is released from the template
and the DNA strands close up and
reform the double helix.
The mRNA made in transcription
leaves the nucleus and takes its
sequence to the ribosome for
protein synthesis (translation).
Translation
Step 1: Initiation: mRNA is inserted into the small subunit
of a ribosome (at the 5l end). When the RNA encounters
the start sequence (AUG) , an initiator tRNA binds to the
ribosome.
Step 2: Elongation- tRNA reads the
codons (3 nucleotide sequence that
codes for amino acids), binding
anticodons to the mRNA strand &
linking amino acids together.
Step 3: Termination- The end of
translation occurs when the ribosome
reaches a STOP codon (UAA, UAG,
UGA). There are not any anticodons
for the STOP codons. The long chain
of amino acids (a polypeptide) is then
released from the ribosome.