Download 12-3: RNA

12-3: RNA
_______ is very similar to DNA; but there are some differences:
DNA
RNA
Structure
Double-stranded
_____________-stranded
Bases- Purines
Adenine (A)
Adenine (A)
Guanine (G)
Guanine (G)
Bases- Pyrimidines Cytosine (C)
Cytosine (C)
Thymine (T)
______________l (U)
Sugar
________________ Ribose
 The main job of RNA is to make _______________ (protein synthesis)
Types of RNA
 There are three main types of RNA: messenger RNA, ribosomal RNA, and transfer RNA.
1) messenger RNA (__________)- molecules of RNA that carries instructions from the
gene (DNA) in the _________________ to the ribosome
2) ribosomal RNA (rRNA)- molecule of RNA that combines with proteins to form the
________________; the ribosome is where __________________ are made
3) transfer RNA (tRNA)- RNA molecule transfers each ______________ to the ribosome
as it is specified by coded messages in mRNA during the construction of a protein
Protein Synthesis Overview
There are two main steps to protein synthesis: 1) Transcription (_______________)
 DNA RNA
2) Translation (________________)
 RNA protein
Transcription
1) Transcription begins when the enzyme RNA polymerase binds to DNA at a promoter region.
 Promoters are signals in ________ that indicate to the enzyme where to bind to make RNA.
2) The enzyme separates the DNA strands by breaking the __________ bonds,
and then uses one strand of DNA as a template from which nucleotides
are assembled into a strand of RNA.
3) RNA polymerase pairs up free-floating ____ nucleotides with DNA template
and joins the nucleotides together to form the backbone of the new
mRNA strand.
 The strand continues to lengthen.
4) When mRNA hits a termination sequence, it separates from the DNA.
5) Then the _________ leaves the nucleus and enters the cytoplasm
Transcription vs. Replication
 The main difference between transcription and DNA replication is that
transcription results in the formation of one single-stranded RNA molecule
rather than a _____________-stranded DNA molecule.
 Practice
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DNA template
ATTCGGAGC
DNA Complement (replication) ____________
mRNA (transcription)
____________
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The Genetic Code
Proteins (polypeptides) are long chains of _________________ that are
joined together.
There are ____ different amino acids.
The properties (structure and function) of proteins are determined
by the order in which different amino acids are joined together to
produce polypeptides.
The four bases (letters) of mRNA A, U, G, and C are read three letters
at a time (and translated) to determine the order in which amino acids
are added to a protein.
A _________ consists of three consecutive nucleotides that specify a single
amino acid that is to be added to the polypeptide (protein).
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The Codon Table
Sixty-four combinations are possible when a sequence of three bases
are used; thus, 64 different mRNA _________ are in the genetic code.
Some codons do not code for amino acids; they provide instructions
for making the protein.
More than one codon can code for the same amino acid.
However, for any one codon, there can be only one amino acid.
All organisms use the ___________ genetic code (A,T,C,G).
o This provides evidence that all life on Earth evolved from a
common ______________.
Cracking the Code
The _______________ code shows the amino acid to which each
of the 64 possible codons corresponds.
To decode a codon, start at the middle of the circle and move outward.
o Ex: CGA _________________
o
Ex: GAU _________________
Translation
 Translation takes place on ___________________, in the cytoplasm.
 The cell uses information from messenger RNA to produce proteins, by _______________ the mRNA message into a
polypeptide chain (protein).
Messenger RNA
1) The mRNA that was transcribed from DNA during _________, leaves the cell’s nucleus and enters the cytoplasm.
Transfer RNA
2) The mRNA enters the cytoplasm and attaches to a ribosome at the AUG, which is the __________ codon. This
begins _______________________-.
3) The transfer RNA (__________) bonds with the correct amino acid and becomes “charged.” (in the cytoplasm)
4) The tRNA carries the _____________________ to the ribosome.
 Each transfer RNA has an ____________________ whose bases are complementary to a codon on the mRNA
strand. (The tRNA brings the correct amino acid to the ribosome.)
 Ex: The ribosome positions the start codon to attract its anticodon, which is part of the tRNA that binds
methionine.
 The ribosome also binds the next codon and its anticodon.
The Polypeptide “Assembly Line”
5) The ribosome moves along the mRNA and adds more amino acids to the growing ______________ or protein
 The tRNA floats away, allowing the ribosome to bind to another tRNA.
 The ribosome moves along the ___________, binding new tRNA molecules and amino acids
Completing the Polypeptide
6) The process continues until the ___________________ reaches one of the three ________ codons on the mRNA,
and then the ribosome falls off the mRNA.
7) The result is a __________________________ chain or protein that is ready for use in the cell.
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Practice
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DNA template
TAC GGT CCA AAC ACT
DNA Complement (replication)
__________________________
mRNA (transcription)
__________________________
tRNA
__________________________
Amino Acid Sequence (translation) __________________________
12-4: Mutations
Organisms have evolved many ways to protect their DNA from changes.
In spite of these mechanisms, however, changes in the ________ occasionally do occur
Any change in DNA sequence is called a _____________________.
Mutations can be caused by errors in replication, transcription, cell division, or by external agents.
Mutations in reproductive cells
Mutations can affect the reproductive cells of an organism by changing the sequence of nucleotides within a
________ in a sperm or an egg cell.
If this cell takes part in fertilization, the altered gene would become part of the genetic makeup of the offspring.
The mutation may produce a new trait or it may result in a protein that does not work correctly.
Sometimes, the mutation results in a protein that is nonfunctional, and the ______________ may not survive.
In some rare cases a gene mutation may have positive effects.
Mutations in body cells
What happens if powerful radiation, such as gamma radiation, hits the DNA of a nonreproductive cell, a cell of the
body such as in skin, muscle, or bone?
If the cell’s DNA is changed, this mutation would ______ be passed on to offspring.
However, the mutation may cause problems for the individual.
Damage to a gene may impair the function of the _______.
When that cell divides, the new cells also will have the same mutation
Some mutations of DNA in body cells affect genes that control cell division.
This can result in the cells growing and dividing rapidly, producing _____________.
The effects of point mutations
A point mutation is a change in a _____________ base pair in DNA.
A change in a single nitrogenous base can change the entire structure of a protein because a change in a single
amino acid can affect the shape of the protein.
Gene Mutations
Substitution
Insertion
Deletion
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Frame shift mutations
What would happen if a single base were lost from a DNA strand?
This new sequence with the deleted base would be transcribed into mRNA. But then, the mRNA would be out of
position by one base.
As a result, every ______________ after the deleted base would be different.
This mutation would cause nearly every amino acid in the protein after the deletion to be changed.
A mutation in which a single base is added or deleted from DNA is called a ___________________ mutation
because it shifts the reading of codons by one base.
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Chromosomal Alterations
Changes may occur in chromosomes as well as in genes.
Alterations to chromosomes may occur in a variety of ways.
Structural changes in chromosomes are called _____________________ mutations.
Chromosomal mutations occur in all living organisms, but they are especially common in _____________.
o Few chromosomal mutations are passed on to the next generation because the zygote usually dies
o In cases where the zygote lives and develops, the mature organism is often __________ and thus
incapable of producing offspring. (This prevents the organism from passing on this mutation to its
offspring).
Examples:
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When a part of a chromosome is left out, a _____________________ occurs.
Deletion
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When part of a chromatid breaks off and reattaches to its sister chromatid, an insertion occurs.
The result is a ______________________ of genes on the same chromosome.
Duplication
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When part of a chromosome breaks off and reattaches backwards, an _____________________ occurs
Inversion
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When part of one chromosome breaks off and is added to a different chromosome, a _________________ occurs.
Translocation
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Causes of Mutations
Some mutations seem to just happen, perhaps as a mistake in base pairing during DNA replication.
o These mutations are said to be ____________________________.
However, many mutations are caused by factors in the environment.
Any agent that can cause a change in DNA is called a ___________________
o Mutagens include radiation, chemicals, and even high temperatures
o Forms of radiation, such as X rays, cosmic rays, ultraviolet light, and nuclear radiation, are dangerous
mutagens because the energy they contain can damage or break apart DNA.
The breaking and reforming of a double-stranded DNA molecule can result in __________________
Chemical mutagens include dioxins, asbestos, benzene, and formaldehyde, substances that are commonly found
in buildings and in the environment.
o Chemical mutagens usually cause substitution mutations
Repairing DNA
Repair mechanisms that fix mutations in cells have evolved.
Enzymes proofread the DNA and replace incorrect nucleotides with correct nucleotides.
These repair mechanisms work extremely well, but they are not perfect.
The greater the exposure to a mutagen such as UV light, the more likely is the chance that a mistake will _______
be corrected.
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