Download Chapter 13 Section 3: RNA and Gene Expression

Chapter 13 Section 3:
RNA and Gene Expression
Key Vocabulary
Terms
Adapted from Holt Biology 2008
RNA
Ribonucleic acid, plays
a role in protein
synthesis
Gene Expression
The manifestation of the
genetic material of an
organism in the form of
specific traits.
Gene expression
produces proteins by
transcription and
translation.
Transcription
The process of forming
a nucleic acid (RNA) by
using another molecule
as a template.
DNA is used to make
RNA
Codon
In mRNA, the three-nucleotide sequence that
codes for an amino acid, or signifies a start or
a stop signal
Chapter 13 Section 3:
RNA and Gene Expression
Supplementary Words
Adapted from Holt Biology 2008
Uracil (U)
An organic compound of the pyrimidine
family that occurs as a component of
ribonucleic acid (RNA), bonds with
adenine
Transfer RNA (tRNA)
An RNA molecule that transfers amino acids to
the growing end of a polypeptide chain during
translation
Ribosomal RNA (rRNA)
The RNA component of the ribosome (P site & A
site). Ribosomal RNA provides a mechanism for
decoding mRNA into amino acids and interacts
with tRNAs during translation.
Messenger RNA (mRNA)
A molecule of RNA encoding a chemical "blueprint"
for a protein product. mRNA is transcribed from a
DNA template, and carries coding information to the
sites of protein synthesis: the ribosome's.
RNA polymerase
An enzyme that starts
(catalyzes) the formation
of RNA by using a strand
of a DNA molecule as a
template
Promoter
A nucleotide
sequence on a DNA
molecule to which an
RNA polymerase
molecule binds, which
initiates the
transcription of a
specific gene
Amino acids
Any one of 20 different
organic molecules that
contain a carboxyl and
an amino group and
that combine to form
proteins
Genetic code
The rule that describes how a
sequence of nucleotides
specifies the amino acid
sequence of a protein
It is read in groups of three
consecutive nucleotides
(triplets) that correspond to
specific amino acids.
Polypeptide
A long chain of several amino acids
Anticodon
A region of tRNA that consists of
three bases complementary to the
codon of mRNA
Stop codon
In an mRNA molecule, a
sequence of three
nucleotides (UUA, UAG, and
UGA) that does not encode
an amino acid and therefore
stops protein synthesis
Chapter 13
Section 3:
RNA and Gene Expression
Notes
Adapted from Holt Biology 2008
Central Dogma
–DNA makes more DNA by ____________
Replication
Transcription
–DNA makes RNA by ___________
–RNA helps make protein by ___________.
Translation
An Overview of Gene Expression
DNA provides the original information from which
proteins are made in a cell, but DNA does not directly
make proteins.
Ribonucleic acid, or RNA, is a second type of nucleic
acid which takes the information from DNA and makes
proteins.
Gene expression
produces
proteins by
transcription
and
translation.
Both stages
involve RNA.
Your Turn Activity
RNA: A Major Player
• All of the steps in gene expression
involve RNA.
• In cells, three types of RNA complement
DNA and translate the genetic code into
proteins.
• Like DNA, RNA is made of nucleotide
subunits linked together.
RNA differs from DNA in
3 ways:
1st, RNA is composed of
one strand of nucleotides
DNA= two strands
RNA differs from DNA in 3 ways:
2nd, RNA nucleotides contain the fivecarbon sugar ribose.
DNA = deoxyribose
RNA differs from DNA in 3 ways:
3rd, RNA nucleotides have a nitrogenous
base called uracil (U)
DNA = base thymine (T)
Uracil (U) is complementary to adenine (A)
whenever RNA pairs with another nucleic
acid.
There are 3 main types of RNA:
Messenger RNA
(mRNA),
Transfer RNA
(tRNA),
& Ribosomal RNA
(rRNA).
Messenger RNA (mRNA) is produced when
DNA is transcribed into RNA. Carries
instructions for making a protein, and
delivers instructions.
Transfer RNA (tRNA) at the site of
translation “reads” the instructions
carried by the mRNA, then translates
the mRNA sequence into protein
subunits called amino acids.
Ribosomal RNA (rRNA) is an RNA
molecule that is part of the structure of
ribosomes.
Ribosomes are the cellular structure
where protein production occurs.
6
Transcription: Reading the Gene
During transcription,
the information in a
specific region of DNA
(a gene) is transcribed,
or copied, into mRNA.
Transcription: Reading the Gene
Transcription is carried
out by a enzyme called
RNA polymerase.
2
Transcription: Reading the Gene
Transcription begins when RNA polymerase
binds to the specific DNA sequence in the
gene that is called the promoter.
Transcription: Reading the Gene
RNA polymerase then
unwinds and separates
the two strands of the
double helix to expose
the DNA bases on each
strand.
Transcription: Reading the Gene
RNA polymerase
moves along the
bases on the DNA
strand and adds
complementary
RNA bases as it
“reads” the DNA
of the gene.
Transcription: Reading the Gene
As RNA polymerase
moves down the
DNA strand, a
single strand of
mRNA grows.
Transcription: Reading the Gene
Behind the moving
RNA polymerase,
the two strands of
DNA close up and
re-form the double
helix.
Transcription is not the same process
as replication.
Transcription = a new molecule of RNA is
made from the DNA.
In DNA replication= a new molecule of DNA
is made from the DNA.
Transcription
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The Genetic Code: Three-Letter
“Words”
• codon = three-nucleotide sequence in mRNA
Each codon corresponds to 1 of 20 amino acids.
• Codons may act as a start or stop signal for translation.
6th
The Genetic Code: Three-Letter
“Words”
• There are 64 mRNA codons. Each codon specifies only
one amino acid, but several amino acids have more
than one codon.
• This system of matching codons and amino acids is
called the genetic code. The genetic code is based on
codons that each represent a specific amino acid.
4th,
7th
The Genetic Code: Three-Letter
“Words”
There are 64 mRNA
codons. Each codon
specifies only one amino
acid, but several amino
acids have more than
one codon.
5th
Codons in mRNA
Translation: RNA to Proteins
• Translation
– occurs in a sequence of steps,
– involves three kinds of RNA
– results in a complete polypeptide (protein).
• Translation takes place in the cytoplasm
• A specific amino acid is added to one end of each
tRNA. The other end of the tRNA has an anticodon.
• An anticodon is a three-nucleotide sequence on
tRNA that is complementary to an mRNA codon.
4&5
Translation: RNA to Proteins, continued
• The mRNA joins with a ribosome and tRNA.
• A tRNA molecule that has the correct anticodon and
amino acid binds to the second codon on the mRNA.
• A peptide bond forms between the two amino acids,
and the first tRNA is released from the ribosome.
• The ribosome then moves one codon down the
mRNA.
Translation: RNA to Proteins, continued
• The amino acid chain continues to grow as each
new amino acid binds to the chain and the
previous tRNA is released.
• This process is repeated until one of three stop
codons is reached.
– A stop codon does not have an anticodon, so
protein production stops.
• Many copies of the same protein can be made
rapidly from a single mRNA molecule because
several ribosomes can translate the same mRNA
at the same time.
Translation: RNA to Proteins
Complexities of Gene Expression
• The relationship between genes and their effects is
complex.
• Some genes are expressed only at certain times or
under specific conditions.
• Variations and mistakes can occur at each of the steps
in replication, transcription, and translation.
• The final outcome of gene expression is affected by
– the environment of the cells
– the presence of other cells
– the timing of gene expression
A bundle of DNA is supported by two
silicon pillars.
DNA's double-helix structure is on display for the first
time in this electron microscope photograph of a small
bundle of DNA strands.