Nucleic Acids and Protein
Synthesis
Modern Biology – Chapter 10
I. Molecular Biology Processes
A. Replication -- copying of DNA
1. Occurs in nucleus
2. Identical DNA strand is made
B. Transcription -- DNA to mRNA
1. (mRNA) copied to move outside
nucleus
C. Translation -- of message into protein
sequence
1. Occurs in the cytoplasm at the
ribosome
2. Amino acids are assembled to
a. Proteins - physical structure
b. enzymes - catalyze other molecules in body
Scientists involved with discovering
the double helix
Many scientists figured
out a piece to the puzzle
1. Most notable:
Watson and Crick
2. Also: Rosalind Franklin
and Maurice Wilkins
DNA – Deoxyribonucleic Acid
A. Organic molecule that
carries the blueprints of
living organisms
1. Stores and transmits the
genetic information
2. Controls the production
of protein
B. Composed of repeating
subunits - nucleotides
Nucleotides
A. Each nucleotide has three parts
1. A five – carbon sugar called deoxyribose
2. A phosphate group (phosphorous
surrounded by oxygen)
3. A nitrogen base (4 kinds)
a. adenine, guanine, thymine, cytosine
Nitrogen Bases
4. Purines
a. Adenine and guanine
b. Contain a double ring
of carbon and nitrogen
5. Pyrimidines
a. Thymine and cytosine
b. Contain a single ring
of carbon and nitrogen
DNA Structure
DNA Structure
• DNA is a double helix – like a spiral
staircase
• Complementary Base Pairing - A weak
hydrogen bond holds nitrogen bases
together:
• Adenine bonds with thymine to form a step
• Cytosine bonds with guanine to form a step
• Deoxyribose sugar and phosphate are
backbone or sides of the ladder –
covalently bonded together
DNA Replication
• Cells that divide must pass exact copies of
their DNA to offspring cells
• Complementary base pairing allows for
complementary nucleotide chains
• This led to the discovery of how DNA
copies itself
• The two nucleotide chains must unwind and
each chain serves as a template for a new
chain
DNA Replication
• First Step – the separation of the two
nucleotide chains
• They separate at a point called the replication
fork
• The chains are separated by helicase enzymes,
which break the hydrogen bonds between the
nitrogen bases
Replication of DNA
• Next Step – the addition of nucleotides to each
side of the unwound DNA molecule
• DNA polymerase enzymes add nucleotides by
covalently bonding a sugar to a phosphate
• Each strand reacts with complimentary bases
floating in the nucleus
• The bases are joined through hydrogen
bonding
• Copying occurs at many points on DNA
Accuracy and Repair of DNA
A. DNA replication is accurate - usually only
1 error in every 10,000 paired nucleotides
B. But any error, called a mutation, can have
serious effects
C. Radiation, chemicals , heat can damage
DNA (mutation)
D. Cell has proofreading techniques – like
spell check
E. Over 20 or more repair enzymes fix errors
Do Now
• What is the function of DNA?
• What are the 4 nitrogen bases in DNA
nucleotides and how do they pair up?
• What are the two main enzymes involved in
DNA replication?
RNA
• The DNA that contains the genetic code to
make all of your proteins is trapped in the
nucleus
• The ribosomes, enzymes, and amino acid
building blocks of protein are out in the
cytoplasm
• RNA is responsible for getting the code
from the nucleus to the cytoplasm
• Copies DNA and then moves outside the
nucleus to synthesize proteins
RNA – Ribonucleic Acid
Like DNA it is made up of repeating
nucleotides
Differences between DNA and RNA:
RNA single stranded
RNA has ribose sugar rather than
deoxyribose
RNA uses Uracil nitrogen base rather than
Thymine to pair with Adenine
Types of RNA
A. Messenger RNA
B. Transfer RNA
C. Ribosomal RNA
Messenger RNA (mRNA)
• Single uncoiled chain of RNA that transmits
DNA’s information from nucleus to cytoplasm
Transfer RNA (tRNA)
• 80 RNA nucleotides folded into a hairpin
shape
• There are ~ 45
different ones
that bind to
specific amino acids
Ribosomal RNA (rRNA)
• Consists of RNA nucleotides in globular form
– most abundant RNA type
• Along with proteins,
rRNA makes up the
ribosomes where
proteins are made
Transcription
• Process by which genetic information is
copied from DNA to mRNA
• An enzyme – RNA polymerase – initiates
transcription by binding to promoter regions
on DNA
• As RNA polymerase binds to promoter, the
DNA molecule separates
• Only one of the DNA strands acts as a
template
Transcription
RNA polymerase connects
RNA bases to the
growing RNA strand
The same as when DNA is
replicated but uracil is
used instead of thymine
It continues until it reaches
a termination signal
Do Now
• How is RNA different from DNA?
• What are the three types of RNA?
• What is the purpose of Transcription?
Translation - Protein Synthesis
• Proteins are polymers of amino acids
• There are 20 different amino acids
• The sequence of amino acids determines the
structure of the protein
• The function of the protein depends on its
structure
Translation - Protein Synthesis
A. The sequence of nucleotides in an mRNA
strand is translated into a sequence of amino
acids to make a protein
B. A series of three nucleotides on RNA, or
codon, codes for one amino acid.
C. There are 64 codons and only 20 amino
acids, so several codons can code for the
same amino acid
D. There are also a start codon (AUG) and
stop codons (UAA, UAG, UGA)
Translation - Protein Synthesis
• mRNA carrying the genetic code from DNA
enters the cytoplasm and meets up with a
ribosome
• Ribosomes bind to mRNA and tRNA
• Amino acids floating in the cytoplasm are
brought to the ribosome by tRNA
Translation - Protein Synthesis
• Each tRNA molecule has a region that bonds
to a specific amino acid
• Each tRNA also has a sequence of three
nucleotides called the anticodon
• The anticodon is complementary to and pairs
up with a corresponding mRNA codon.
Translation
A. mRNA moves out of the nucleus
B. mRNA goes to ribosomes and attaches to start codon
(AUG)
C. tRNA moves amino acids in cytosplam to ribosome
D. tRNA anticodon bases pair with codon and drag
amino acid to add to polypeptide
E. Ribosome enzymes create peptide bonds between
amino acids
F. Amino acids are added until stop codon is reached