Download Chapter 13- RNA and Protein Synthesis

Chapter 13- RNA
and Protein
Synthesis
Grade 11
Honors Biology
Beijing Royal School
• Describe how RNA differs from DNA
• Explain the functions of RNA
• Describe how cells synthesize RNA
I. 13.1 RNA
A. The Role of RNA
1. How does RNA differ
from DNA?
a. RNA- is a nucleic acid
that consists of long
chains of nucleotides
b. Made up of a 5 carbon
sugar, a phosphate
group, and nitrogenous
bases
c. Comparison- key differences
DNA
• Sugar is
deoxyribose
• Is double
stranded
• Contains
thymine
RNA
• Sugar is
ribose
• Is single
stranded
• Contains
uracil instead
of thymine
2. Role Analogy
a. Builders use plans to build a home
• DNA = the master plan – too valuable to bring
to the job site
• RNA = blueprint- inexpensive and disposable
• The master plan is used to prepare the
blueprints
3. Functions of RNA
a. Major job- protein synthesis
b. Controls the assembly of amino acids into
proteins
c. The 3 different
types of RNA
• Messenger “m”
RNA
• Ribosomal “r”
RNA
• Transfer “t”
RNA
d. Roles of the 3 Types of RNA
• mRNA- carry information from DNA to other
parts of the cell
• rRNA- make up the subunits of the ribosome;
worktable for making protein
• tRNA- carries amino acids to the ribosome and
matches them to the coded mRNA message
B. RNA Synthesis
1. How does the cell make mRNA?
a. Transcription – segments of DNA serve as templates
to produce complimentary RNA molecules
• The base sequences of transcribed RNA complement
the base sequences of the DNA template
• In prokaryotes,
transcription takes
place in the
cytoplasm
• In eukaryotes, it
takes place in the
nucleus
• Transcription requires an enzyme- RNA
polymerase
• RNA polymerase binds to DNA and separates the
2 strands
• Next, it uses one strand of DNA to make a
template in RNA
• One gene can produce 100’s-1,000’s of RNA
molecules
MIT – Lego Transcription
b. Promoters
• RNA polymerase
bonds only to
promoters
• This tells RNA
polymerase where to
start and stop
transcription
• Promoters are signals
in the DNA
molecule’s sequence
Transcription animation
c. RNA editing
• RNA molecules require some editing before being
read
• Introns- the pieces that are edited out of the premRNA molecule
• Exons- the remaining pieces after the pre-mRNA
molecule has been edited
• Describe how RNA differs from DNA
• Explain the functions of RNA
• Describe how cells synthesize RNA
• Describe how the genetic code is read
• Explain the role of ribosomes in assembling
proteins
• Describe the “central dogma” of molecular biology
II. 13.2 Ribosomes and Protein Synthesis
A. The Genetic Code
1. What is the genetic code,
and how is it read?
a. First step- transcribe the
base sequences from
DNA to RNA
b. RNA then must be
translated into
polypeptides, which form
proteins
c. Polypeptides- a long chain of amino acids that
makes protein
• There are 20 amino acids commonly found in
proteins
• The properties of a protein depend on the order
in which the amino acids are assembled
• The 4 bases (A, U, C, G) in
RNA form a “language”
• These bases form the genetic
code
• The sequence of bases is read
a codon at a time
• Codons contain 3 bases
• Each codon specifies a single
amino acid to be added to
the polypeptide chain
2. How to Read Codons
a. There are 4
different bases in
RNA, which means
there are 64
possible codons
• 4 x 4 x 4 = 64
possibilities
•
•
•
Most amino acids
can be specified by
more than one codon
Ex: Leucine can be
coded for in 6 ways:
UUA, UUG, CUU,
CUC, CUA, and CUG
Genetic code tables
are used to decode
codons
3. Start and Stop Codons
a. AKA the “punctuation
marks” of the genetic
code
b. The methionine codon
AUG = start
c. mRNA is then read 3
bases at a time until it
reaches a “stop” codon.
d. Once stopped the
polypeptide is complete
B. Translation (p. 368 – 369)
1. What role does the
ribosomes play in
assembling proteins?
a. Analogy: putting
together a complex
toy
• Need to read the
directions AND put
the parts together
• Ribosomes carry out
these tasks in a cell
Lego Translation
Translation
animation
• Ribosomes use the sequence of codons in mRNA
to assemble amino acids into polypeptide chains
• Translation – the decoding of the mRNA
message into protein
2. Steps in Translation
a. Transcribed mRNA from the nucleus moves
into the cytoplasm to attach to a ribosome
b. Codons pass through the ribosome and tRNAs
bring the proper amino acids into the ribosome
c. Each tRNA molecule carries just one kind of
amino acid
• tRNA has 3 unpaired nitrogen bases = anticodon
• So, each tRNA anticodon is complimentary to
one mRNA codon
• Ex: tRNA anticodon is UAC, the mRNA codon is
AUG
d. Like an assembly-line worker that attaches one
part to another, the ribosome helps form a peptide
bond between the amino acids
e. The chain continues to grow with each tRNA
coming in until it reaches the “stop” codon on
mRNA
f. The ribosome then releases the protein and the
mRNA
3. The Roles of tRNA and rRNA in Translation
a. All 3 major forms of RNA work together to
make protein synthesis occur
b. mRNA brings the DNA message out of the
nucleus
c. The tRNA deliver the amino acid called for by
the mRNA
d. The rRNA are part of the ribosome and help
locate the “start” code of the mRNA message
C. The Molecular Basis of Heredity
1. What is the central dogma of molecular
biology?
a. Information is transferred from DNA to RNA to
protein
Summary
b. Protein has everything to do with how genes are
expressed
• Ex: A gene that codes for an enzyme to produce
pigment can control the color of a flower
c. Gene expression – the way in which DNA, RNA,
and proteins are involved in putting genetic
information into action in living cells
d. It’s universal!
• Describe how the genetic code is read
• Explain the role of ribosomes in assembling
proteins
• Describe the “central dogma” of molecular biology
• Describe what a mutation is
• Explain how mutations affect genes
III. 13.3 Mutations
A. Types of Mutations
1. What are mutations?
a. From Latin “mutare”meaning to change
b. Defined: any heritable
change in the genetic
information
c. Two types
• gene
• chromosome
2. Gene Mutations
a. Point mutations – mutation where a single or
very few nucleotides are changed
• Include substitutions, deletions, and insertions
• Usually occur during replication of DNA
b. Substitutions
• One base is changed to a different base
• Usually affect no more than a single amino acid
• Sometimes have no effect at all
Analogy:
Original
The fat cat ate the wee rat.
Point Mutation
The fat hat ate the wee rat.
c. Insertions and deletions
• One base is either inserted or removed from the
DNA sequence
• Effects can be dramatic
• Can lead to frameshift mutations
Analogy 1:
Original
The fat cat ate the wee rat.
Analogy 2:
Original
The fat cat ate the wee rat.
Frame Shift
The fat caa tet hew eer at.
Insertion
The fat cat xlw ate the wee rat.
3. Chromosomal Mutations
a. Involve changes in the
number or structure of
chromosomes
• Can change the location
of genes or even the
number of
chromosomes
b. Different types
• Deletion, duplication,
inversion, translocation
Animation link
B. Effects of Mutations
1. How do mutations affect genes?
a. Genetic information can be altered by natural
events or by artificial means
• Fact: Incorrect bases are routinely copied
during DNA replication at a rate of
1/10,000,000
2. Mutagens
a. defined: chemical or physical agents in the
environment
• Chemical examples: pesticides, plant alkaloids,
tobacco smoke, pollutants
• Physical examples: radiation like X-rays and
UV light
3. Harmful and Helpful Mutations
a. The effects of mutations on genes vary widely.
• Some have little effect
• Some are beneficial
• Some negatively disrupt gene function
• Most have little or no effect
b. Effect is situational
c. Can generate variability within a species
d. Harmful effects
• The most harmful effects come when the
structure of a protein is dramatically changed
• These can disrupt normal body routines
• Can result in genetic disorders
• Ex: Cystic Fibrosis
e. Beneficial Effects
• Sometimes mutations can produce proteins with
new or altered functions that can be useful to an
organism in a changing environment
• Ex: mutations have allowed certain insects to be
resistant to pesticides – like mosquitoes
• Plant and animal breeders make good use of
mutations
• Non-disjunction in plants
during meiosis can be a
beneficial mutation
• Leads to the formation of
polyploid plants
• Plants can be triploid or
tetraploid
• Ex: bananas, citrus,
sugarcane, grains, etc…
Strawberries are octoploid
8N = 56
2N = 7
Mutations in Mammals
Siamese cat- the protein that
produces fur color is
dependent on heat. This is
caused by a mutation in one
gene
White Appaloosa horse- color
is caused by a mutation in
one gene
Mutations in “Herps”
Leucistic alligator, three legged
frog
tomatoes
Seedless grapes
• Describe what a mutation is
• Explain how mutations affect genes
• Explain how genes are regulated in prokaryotic
and eukaryotic organisms
• Describe the controls placed on the development
of tissues
IV. 13.4: Gene Regulation and Expression
A. How are genes
regulated?
1. In prokaryotes DNA
binding proteins
regulate genes by
controlling
transcription
2. Genes are
organized into
operons: groups of
genes that are
regulated together
a. On the operon are
regulatory regions
• Promoters – site
where RNA
polymerase binds
for transcription
• Operators – site
where a DNA
binding protein can
attach; analogy: car
boot
Gene expression animation
B. The Promise of RNAi Technology
1. RNA interference has an important role in
defending cells against parasitic genes –
viruses
2. Also is important in directing development
as well as gene expression in general.
3. Looks like a promising new method to
treat various diseases like HIV and cancer
Step
RNAthrough
I short film RNAi model
RNAi short film 2
• Explain how genes are regulated in prokaryotic
and eukaryotic organisms
• Describe the controls placed on the development
of tissues