Download RNA and Protein Synthesis

PROTEIN
SYNTHESIS
Or…how our bodies make
proteins!
What is the function of
DNA
• The DNA molecule contains all
•
•
•
•
your hereditary information in
the form of genes
A gene is a coded section of
DNA; it tells our cells how to
build specific proteins
Genes code for EVERYTHING
our body needs and does
(saliva, bones, eye shape)
Because DNA is so large, it is
stuck inside the nucleus
It needs a messenger to move
the information from nucleus to
protein production locations
(ribosomes!)
http://www.accessexcellence.org/RC/VL/GG/images/genes.gif
What is the history of DNA
• Chromosomes are made of both DNA
and protein
• DNA is made up of nucleotides, which
consists of a nitrogen base, a pentose
sugar, and a phosphate group.
• Proteins were composed of 20
different amino acids in long
polypeptide chains
3
History of DNA
• Two strands coiled
called a double helix
• Center made of nitrogen
bases bonded together
by weak hydrogen bonds
4
What is the rule for DNA
• Adenine must pair with
Thymine
• Guanine must pair with
Cytosine
• The bases form weak
hydrogen bonds
T
A
G
copyright cmassengale
C
5
What is RNA!
• RNA is a nucleic acid
messenger between DNA
and ribosomes
• 3 differences between
DNA and RNA:
– RNA has ribose sugar
– RNA is single stranded
– RNA contains a nitrogen
base called uracil (U)
instead of thymine.
http://www.dkimages.com/discover/previews/769/85011519.JPG
What is the rule for RNA
• Adenine must pair with Uracil
• Guanine must pair with
Cytosine
• The bases form weak
hydrogen bonds
U
A
G
copyright cmassengale
C
7
DNA
- Double stranded
molecule
- Contains thymine
- Contains deoxyribose
sugar
- Found only in nucleus
RNA
- Made of
nucleotides
- Contain adenine,
guanine, and
cytosine
- Single stranded
molecule
- Contains uracil
- Contains ribose
sugar
- Found in nucleus
and cytoplasm
Does this diagram represent DNA
or RNA? …how can you tell?
You are a
What are the 3 types of
RNA
• Messenger RNA (mRNA):
– copies DNA in the nucleus and carries the info to the ribosomes
(in cytoplasm)
• Ribosomal RNA (rRNA):
– makes up a large part of the ribosome; reads and decodes
mRNA
• Transfer RNA (tRNA):
– carries amino acids to the ribosome where they are joined to
form proteins
What is Protein
synthesis
• Protein synthesis is the assembly of amino
acids (by RNA) into proteins
• Involves two steps:
– 1. Transcription – copying DNA code into mRNA
– 2. Translation – reading the mRNA code and
assembling amino acids into a polypeptide chain
(protein)
How transcription works
1. DNA strand splits,
exposing the active
strand
2. Complementary
mRNA nucleotides
line up opposite the
active strand, forming
mRNA
3. mRNA leaves the
nucleus
Transcription demo
What is the Semiconservative
Model of Replication
• Method of DNA replication in which
parental strands separate, act as
templates, & produce molecules of
DNA with one parental DNA strand &
one new DNA strand
• New DNA consists of 1
PARENTAL (original) and 1 NEW
DNA Template
strand of DNA
Parental DNA
New DNA
copyright cmassengale
14
Decoding mRNA (translation)
• The sequence of bases in an mRNA molecule
serves as instructions for the order in which
amino acids are joined to produce a polypeptide
• Ribosomes decode the instructions by using
codons, sets of 3 bases that each code for 1
amino acid
• Each codon is matched to an anticodon, or
complementary sequence on the tRNA to
determine the order of the amino acids
• Translation demo
Using a codon chart
http://www.safarikscience.org/biologyhome/7_dna/codon_qu
estion.png
• A codon chart is used to determine the
sequence of the amino acids in the polypeptide
• The sets of 3 mRNA bases (codons) are used to
find the amino acid
Decoding Practice
For the following DNA examples, first give the
appropriate mRNA sequence, then identify the amino
acid sequence (remember: U replaces T in mRNA)
Example 1:
DNA:
TAC GCA TGG AAT
mRNA:
AUG CGU ACC UUA
Amino Acids:
Met Arg
Thr
Leu
Example 2:
DNA:
CGT GGA GAT ATT
mRNA:
GCA CCU CUA UAA
Amino Acids:
Ala Pro
Leu
stop
Translation Review
DNA replication is very accurate
• DNA polymerase laying down new nucleotides
makes1 error per 1,000,000 nucleotides
• Sounds good?
• 3,000,000,000 base pairs in the each human
cell…3,000 possible errors each time our cells
replicate
• BUT…after DNA Polymerase is done, other
enzymes “proofread” and correct the new strand
• Afterward, the error rate is about 1 error per
10,000,000,000 or 1 error every 3 cell divisions.
Replication practice
TTGGCC A
G
AGAT
AT
DNA
DNA
polymeras
epolymerase
helicase
A ACCGGTT CC T
T
new
new
strands
strands
old
old
strands
strands
Environmental Influences
– In prokaryotes and eukaryotes,
environmental factors like temperature,
salinity, and nutrient availability can influence
gene expression.
– For example, the lac operon in E. coli is
switched on only when lactose is the only
food source in the bacteria’s environment.
Environmental Influences
– Metamorphosis is another example of
how organisms can modify gene
expression in response to their
environment.
– Metamorphosis involves a series of
transformations from one life stage to
another, such as the transformation of a
tadpole to an adult bullfrog. It is typically
regulated by a number of external
(environmental) and internal (hormonal)
factors.
Environmental Influences
– As organisms move from larval to adult
stages, their body cells differentiate to
form new organs.
– At the same time, old organs are lost
through cell death.
Environmental Influences
– For example, under less than ideal
conditions—a drying pond, a high density of
predators, low amounts of food—tadpoles
may speed up their metamorphosis.
– The speed of metamorphosis is determined
by various environmental changes that are
translated into hormonal changes, with the
hormones functioning at the molecular level.
What are Mutations
–Mutations are heritable
changes in genetic
information.
Types of Mutations
– All mutations fall into two basic categories:
– Those that produce changes in a single gene
are known as gene mutations.
– Those that produce changes in whole
chromosomes are known as chromosomal
mutations.
Gene Mutations
– Mutations that involve changes in one or a
few nucleotides are known as point
mutations because they occur at a single
point in the DNA sequence. They generally
occur during replication.
– If a gene in one cell is altered, the alteration
can be passed on to every cell that develops
from the original one.
Gene Mutations
– Point mutations include substitutions,
insertions, and deletions.
Substitutions
– In a substitution, one base is changed to a
different base.
– Substitutions usually affect no more than a
single amino acid, and sometimes they have
no effect at all.
Substitutions
– In this example, the base cytosine is
replaced by the base thymine, resulting in a
change in the mRNA codon from CGU
(arginine) to CAU (histidine).
– However, a change in the last base of the
codon, from CGU to CGA for example, would
still specify the amino acid arginine.
Insertions and Deletions
– Insertions and deletions are point mutations
in which one base is inserted or removed from
the DNA sequence.
– If a nucleotide is added or deleted, the bases
are still read in groups of three, but now those
groupings shift in every codon that follows the
mutation.
Insertions and Deletions
– Insertions and deletions are also called
frameshift mutations because they shift the
“reading frame” of the genetic message.
– Frameshift mutations can change every
amino acid that follows the point of the
mutation and can alter a protein so much that
it is unable to perform its normal functions.
What are Chromosomal
Mutations
– Chromosomal mutations involve changes in
the number or structure of chromosomes.
– These mutations can change the location of
genes on chromosomes and can even
change the number of copies of some genes.
– There are four types of chromosomal
mutations: deletion, duplication, inversion,
and translocation.
What is deletion
– Deletion involves the loss of all or part of a
chromosome.
What is duplication
– Duplication produces an extra copy of all or
part of a chromosome.
What is inversion
– Inversion reverses the direction of parts of a
chromosome.
What is translocation?
– Translocation occurs when part of one
chromosome breaks off and attaches to
another
–.
What are Mutagens
– Some mutations arise from mutagens,
chemical or physical agents in the
environment.
– Chemical mutagens include certain
pesticides, a few natural plant alkaloids,
tobacco smoke, and environmental pollutants.
– Physical mutagens include some forms of
electromagnetic radiation, such as X-rays and
ultraviolet light.
How do mutations affect genes?
Some have little or no effect; and some
produce beneficial variations. Some negatively
disrupt gene function.
– Mutations often produce proteins with new or
altered functions that can be useful to
organisms in different or changing
environments.
Effects of Mutations
– Genetic material can be altered by natural
events or by artificial means.
– The resulting mutations may or may not affect
an organism.
– Some mutations that affect individual
organisms can also affect a species or even an
entire ecosystem.
Effects of Mutations
– Many mutations are produced by errors in
genetic processes.
– For example, some point mutations are
caused by errors during DNA replication.
– The cellular machinery that replicates DNA
inserts an incorrect base roughly once in every
10 million bases.
– Small changes in genes can gradually
Effects of Mutations
– Stressful environmental conditions may cause
some bacteria to increase mutation rates.
– This can actually be helpful to the organism,
since mutations may sometimes give such
bacteria new traits, such as the ability to
consume a new food source or to resist a
poison in the environment.
Mutagens
– If these mutagens interact with DNA, they
can produce mutations at high rates.
– Some compounds interfere with basepairing, increasing the error rate of DNA
replication.
– Others weaken the DNA strand, causing
breaks and inversions that produce
chromosomal mutations.
–
Harmful and Helpful
Mutations
The effects of mutations on genes vary widely. Some have little
or no effect; and some produce beneficial variations. Some
negatively disrupt gene function.
–
Whether a mutation is negative or beneficial depends on how its
DNA changes relative to the organism’s situation.
–
Mutations are often thought of as negative because they disrupt
the normal function of genes.
–
However, without mutations, organisms cannot evolve, because
mutations are the source of genetic variability in a species.
Harmful Effects
– Some of the most harmful mutations are
those that dramatically change protein
structure or gene activity.
– The defective proteins produced by these
mutations can disrupt normal biological
activities, and result in genetic disorders.
– Some cancers, for example, are the product
of mutations that cause the uncontrolled
growth of cells.
Harmful Effects
– Sickle cell disease is a disorder associated
with changes in the shape of red blood cells.
Normal red blood cells are round. Sickle
cells appear long and pointed.
– Sickle cell disease is caused by a point
mutation in one of the polypeptides found in
hemoglobin, the blood’s principal oxygencarrying protein.
– Among the symptoms of the disease are
Beneficial Effects
– Some of the variation produced by mutations
can be highly advantageous to an organism
or species.
– Mutations often produce proteins with new or
altered functions that can be useful to
organisms in different or changing
environments.
– For example, mutations have helped many
insects resist chemical pesticides.
Beneficial Effects
– Plant and animal breeders often make use of
“good” mutations.
– For example, when a complete set of
chromosomes fails to separate during
meiosis, the gametes that result may produce
triploid (3N) or tetraploid (4N) organisms.
– The condition in which an organism has
extra sets of chromosomes is called
polyploidy.
Beneficial Effects
– Polyploid plants are often larger and
stronger than diploid plants.
– Important crop plants—including
bananas and limes—have been produced
this way.
– Polyploidy also occurs naturally in citrus
plants, often through spontaneous
mutations.