DNA, RNA and Protein
Synthesis
Chapter 11
DNA Structure
• DNA is a chain of
Nucleotides
– 3 parts of a Nucleotide:
• sugar (deoxyribose)
• Phosphate
• nitrogen base 4 possible bases:
– Adenine
– Guanine
– Thymine
– Cytosine
Structure of DNA (continued)
• The DOUBLE HELIX (looks like a twisted
ladder)
– Double Stranded–
– 2 sugar/ phosphate backbones
– rungs = nitrogen base pairs
• hydrogen bonds between
complementary nitrogen bases
• complementary= will bond together
– A is complementary to T,
– G is complementary to C
– Base-pairing rules (see above)
• The number and sequence of the nitrogen
bases determines the CODE of the genes in
the DNA!
Video
• http://www.pbs.org/wgbh/nova/body/publicgenomes.html Personal DNA Testing!
• http://www.pbs.org/wgbh/nova/genome/program_a
dv.html Very Good! Show toward end of unit
(discusses genome, mutations etc.)
• S:\Biology\Protein Synthesis\Videos\Genetics
Bill Nye Greatest Genetic Discoveries. Can be started
around here (about 1 hr.)
DNA Replication
• DNA making copies of itself is called DNA
REPLICATION
• Steps of DNA replication are controlled by enzymes.
•
Animation
C:\Documents and Settings\BBAUGHMAN\Desktop\bio powerpoints\Chapter 11 BDOL IC
Enzymes of Replication
• 3 of the main enzymes are:
– Helicase: untwists the DNA
– DNA polymerase: adds new nucleotides and
connects them to build up a new strand (follows
base-pairing rules!)
– Ligase: Joins DNA fragments together
Background info for Protein Synthesis…
• DNA is important
because it is the
instructions for how
to make proteins!
• But…
– DNA can’t make
proteins by itself!
– RNA is needed!
Function of RNA
• accomplish protein
synthesis
• Why?--DNA is
trapped in the nucleus
but protein synthesis
happens at ribosomes
located in cytoplasm.
RNA
RNA
• Structure of RNA
– nucleotide
• sugar= ribose
• phosphate
• nitrogen base (instead of thymine, RNA has Uracil).
– Uracil is complementary to Adenine (it replaces
Thymine)
– Single stranded
Three Types of RNA
– Messenger RNA (mRNA) is
used to take the message from
DNA to the ribosome
– Ribosomal RNA (rRNA)
attaches to mRNA and helps
assemble proteins
– Transfer RNA (tRNA) transfers
(brings) amino acids to mRNA
so that they can be attached to
make a protein
Compare and Contrast DNA and
RNA in the following table
DNA
# strands
RNA
2
1
sugar
Deoxyribose
Ribose
Nitrogen bases
A, C, G, T
function
Code for
proteins
A, C, G, U
Protein
Synthesis
Self Check Quiz
1.
Describe the relationship between DNA and RNA.
-
DNA codes for RNA (i.e. recipes).
RNA makes proteins.
2. List three ways RNA different from DNA.
1) RNA sugar: Ribose
2) RNA single stranded
3) Uracil replaces Thymine (A= U)
3. What would happen if mRNA could not function?
- No mRNA = no message (recipe) from DNA to make protein
- = No protein 
Protein Synthesis
11.2 From DNA to PROTEIN
• I. The Purpose of DNA: DNA is used to make RNA which is
used to make proteins!!
• DNA--> RNA--> Proteins
– A. One DNA molecule has many GENES on it!
– B. Gene—segment of DNA molecule that codes for a
specific protein.
Protein Synthesis Step 1: Transcription
III. TRANSCRIPTION
•Transcription Animation http://highered.mcgraw-hi
– A. Transcription is the
synthesis of mRNA using the
code of a gene (DNA) as a
template (pattern).
– B. Steps
1. An enzyme (RNA
Polymerase) unzips DNA
2. RNA Polymerase attaches
RNA nucleotides following
base pairing rules.
– This makes single
stranded mRNA
3. Single stranded mRNA
leaves the nucleus and goes
to the ribosome.
Protein Synthesis Step 2: Translation
•
IV. Translation (Converting the “language” of
mRNA to the language of proteins.)
Codon= triplet of nitrogen bases on mRNA
•
–
Each codon codes for one specific amino acid
•
•
Note: amino acids are the building blocks of proteins
This code is universal- it applies to all organisms!
Translation continued…
– The order of codons
determines the order of amino
acids found in the protein.
– mRNA from nucleus is ‘read’
along its codons
• this occurs at the ribosome
• tRNA has anticodons that
are complementary to
specific codons
• Each tRNA can only bind
one amino acid
• tRNA transfers or transports
the amino acids to the
ribosome where they are
attached (in order) to make
a polypeptide chain.
Translation Animation http://highered.mcgrawhill.com/sites/0072507470/student_view0/chapter3/animation
__how_translation_works.html
Analogy of Transcription through translation (RNAi explained)
http://www.pbs.org/wgbh/nova/teachers/body/rnaidiscovered.html
http://www.pbs.org/wgbh/nova/sciencenow/3210/02.html
MUTATIONS!
• Any CHANGE in the DNA sequence is a mutation!
• Mutations are caused by mutagens!
•
Types of mutations
– Point mutation—change in a single base pair of
DNA
• May change one amino acid in protein
Animation: http://www.dnalc.org/view/15532-Sickle-cell-anemia-3D-animation-with-narration.html
– frameshift mutation—deletion or addition of a
single base pair.—Causes every codon after the
mutation to be different!!
Great Video (also good intro to
human genome project)
• http://www.pbs.org/wgbh/nova/genome/prog
ram_adv.html Very Good! Show toward end of
unit (discusses genome, mutations etc.)