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Transcript
The Role and Structure of
RNA
Daily Challenge: I CAN analyze
and explain the role that RNA
plays in the production of proteins
through transcription and
translation.
Nucleic Acids
• There are 2 types of nucleic acids.
– DNA or deoxyribonucleic acid
– RNA or ribonucleic acid
• All living things have both DNA and RNA.
• Nucleic acids are made of nucleotides and
carry genetic information.
DNA vs. RNA
• DNA
– Deoxyribonucleic
acid
– Double-stranded
– Sugar = deoxyribose
– Nucleotide Bases:
• Adenine
• Thymine
• Guanine
• Cytosine
• RNA
– Ribonucleic acid
– Single-stranded
– Sugar = ribose
– Nucleotide Bases:
• Adenine
• Uracil
• Guanine
• Cytosine
Purpose of DNA
• DNA can be copied, but that does NOT
explain how a gene works.
• DNA contains coded instructions for
making proteins.
• The first step of making proteins is
decoding the genetic messages by
copying the nucleotide sequence from
DNA into RNA.
Functions of RNA
• In most cells RNA molecules have just one
job — protein synthesis.
• Protein synthesis is the process by which
amino acids are joined together to make
proteins.
• Amino acids are the building blocks of
proteins.
• There are a total of 20 amino acids.
• The assembly of amino acids is controlled
by RNA.
Types of RNA
• There are three types of RNA that each
play an important role in protein synthesis.
• The three types are:
 mRNA — Messenger RNA
 tRNA — Transfer RNA
 rRNA — Ribosomal RNA
Messenger RNA (mRNA)


Messenger RNA serve as messengers from
DNA to the rest of the cell.
They carry copies of the instructions found
on genes.
Transfer RNA (tRNA)


tRNA takes the messages
from mRNA and decodes
them for the ribosome.
During the construction
of a protein, transfer RNA
transfers each amino
acid to the ribosome.
Ribosomal RNA (rRNA)



Proteins are assembled
on ribosomes made of
ribosomal RNA.
Ribosomal RNA helps
build the actual
protein.
rRNA puts together the
amino acid messages
carried by mRNA and
decoded by tRNA.
Protein Synthesis:
An Overview
Daily Challenge: I CAN explain the
processes of transcription and translation as
it relates to the process of protein synthesis.
Protein Synthesis
• Protein synthesis uses the
information in genes to make
proteins.
• There are 2 Steps:
–Transcription
–Translation
Transcription
• DNA is copied into a complementary
sequence of mRNA by the enzyme
RNA Polymerase.
• mRNA leaves the nucleus and goes to
the cytoplasm.
• The mRNA sequence is read in triplets
(group of 3 bases) called “codons.”
• Each codon codes for a specific amino
acid. (Each codon is like a word in a
sentence)
Amino Acid Codon Chart
Transcription
• Transcription requires RNA
polymerase, an enzyme a lot like DNA
polymerase
• RNA polymerase binds to DNA,
separates the strands, and uses one
strand as a template for making mRNA.
• RNA polymerase “polymerizes” (links
together) the nucleotides that make up
mRNA
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA
polymerase
DNA
RNA
Where to Start?
• RNA polymerase doesn’t randomly
bind to DNA.
• It will only bind to sites known as
promoters—regions of DNA that
have specific sequences.
• Promoters are signals that say
“START RNA HERE!”
• Similar signals also tells
transcription to stop.
Start/Stop Codons
• There are 64 different codons.
• Most code for amino acids.
• There will always be a “Start” codon
(AUG) at the beginning. It is like
capitalizing the 1st letter of a sentence.
• There will always be a “Stop” codon
(UGA, UAA, UAG) at the end. It is like a
period at the end of a sentence.
Translation
• tRNA translates the mRNA using
“anticodons.”
• Each tRNA molecule has an anticodon
on one end and an amino acid on the
other.
• tRNA transfers the amino acids to the
ribosome in the correct sequence.
• The ribosome made of rRNA links the
amino acids together to build the
polypeptide chain or protein.
Nucleus
Messenger RNA
Messenger RNA is transcribed in the nucleus.
Phenylalanine
tRNA
mRNA
Lysine
Transfer RNA
The mRNA then enters the cytoplasm and attaches
to a ribosome. Translation begins at AUG, the start
codon. Each transfer RNA has an anticodon
whose bases are complementary to a codon on the
mRNA strand. 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.
Methionine
anticodon
Ribosome
mRNA
Start codon
The Polypeptide “Assembly Line”
The ribosome joins the two amino acids—
methionine and phenylalanine—and breaks the
bond between methionine and its tRNA. The
tRNA floats away, allowing the ribosome to bind
to another tRNA. The ribosome moves along
the mRNA, binding new tRNA molecules and
amino acids.
Lysine
Growing polypeptide chain
Ribosome
tRNA
tRNA
mRNA
Completing the Polypeptide
mRNA
Translation direction
Ribosome
The process continues until the ribosome reaches
one of the three stop codons. The result is a growing
polypeptide chain.
Protein Synthesis Review
• DNA carries the information in the form of genes
to build proteins.
• RNA polymerase copies the DNA strand into
messenger RNA (mRNA) which carries the DNA
message.
• Transfer RNA (tRNA) reads the message of
mRNA, gathers the correct amino acids, and
delivers them to the ribosome for assembly.
• Ribosomal RNA (rRNA) then takes the amino
acids from transfer RNA and links them together
to make the protein.
Remember This!
• DNA is like the master blueprint.
• RNA is like the blueprint copy the
workers use.
• The workers are ribosomes.
• Proteins are the finished product.
• Proteins are the keys to almost
EVERYTHING that living cells do!
Protein Synthesis Activity
• Step 1: Transcription
– Copy the “gene” into the complementary
sequence of mRNA.
– This must be done in the “Nucleus.”
• Step 2: Translation
– Translate the mRNA using the “tRNA cards”
posted around the room. The codon should
match up with a word.
– If you have done this correctly, your sentence
should make sense!!!
– Don’t forget the punctuation (Start/Stop codons)!!