The Role and Structure of The Role and Structure of RNARNA

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.There are 2 types of nucleic acids.– DNA or deoxyribonucleic acidDNA or deoxyribonucleic acid– RNA or ribonucleic acidRNA or ribonucleic acid

• All living things have both DNA and RNA.All living things have both DNA and RNA.

• Nucleic acids are made of nucleotides and Nucleic acids are made of nucleotides and carry genetic information.carry genetic information.

DNA vs. RNADNA vs. RNA

• DNADNA – Deoxyribonucleic Deoxyribonucleic

acidacid– Double-strandedDouble-stranded– Sugar = deoxyriboseSugar = deoxyribose– Nucleotide Bases:Nucleotide Bases:

• AdenineAdenine• ThymineThymine• GuanineGuanine• CytosineCytosine

• RNARNA

– Ribonucleic acidRibonucleic acid

– Single-strandedSingle-stranded

– Sugar = riboseSugar = ribose

– Nucleotide Bases:Nucleotide Bases:

• AdenineAdenine

• UracilUracil

• GuanineGuanine

• CytosineCytosine

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 In most cells RNA molecules have just one job

— — protein synthesisprotein synthesis..

• Protein synthesisProtein synthesis is the process by which is the process by which amino acids are joined together to make amino acids are joined together to make proteins.proteins.

• Amino acids are the building blocks of proteins.Amino acids are the building blocks of proteins.

• There are a total of There are a total of 20 amino acids20 amino acids..

• The assembly of amino acids is controlled by The assembly of amino acids is controlled by RNA.RNA.

Types of RNATypes of RNA

• There are three types of RNA that each There are three types of RNA that each play an important role in protein synthesis.play an important role in protein synthesis.

• The three types are:The three types are: mRNA — Messenger RNAmRNA — Messenger RNA tRNA — Transfer RNAtRNA — Transfer RNA rRNA — Ribosomal RNArRNA — Ribosomal RNA

Messenger RNA (mRNA)Messenger RNA (mRNA)

Messenger RNA serve as messengers Messenger RNA serve as messengers from DNA to the rest of the cell. from DNA to the rest of the cell.

They They carrycarry copies of the copies of the instructionsinstructions found on genes. found on genes.

Transfer RNA (tRNA)Transfer RNA (tRNA)

tRNA takes the tRNA takes the messages from mRNA messages from mRNA and and decodesdecodes them them for the ribosome. for the ribosome.

During the During the construction of a construction of a protein, transfer RNA protein, transfer RNA transferstransfers each amino each amino acid to the ribosome.acid to the ribosome.

Ribosomal RNA (rRNA)Ribosomal RNA (rRNA) Proteins are assembled Proteins are assembled

on ribosomes made of on ribosomes made of ribosomal RNA.ribosomal RNA.

Ribosomal RNA helps Ribosomal RNA helps buildbuild the actual the actual protein. protein.

rRNA puts together the rRNA puts together the amino acid messages amino acid messages carried by mRNA and carried by mRNA and decoded by tRNA.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 Protein synthesis uses the uses the information in genes to make information in genes to make proteins.proteins.

• There are 2 Steps:

–TranscriptionTranscription

–TranslationTranslation

TranscriptionTranscription• DNA is copied into a complementary DNA is copied into a complementary

sequence of mRNA by the enzyme sequence of mRNA by the enzyme RNA RNA Polymerase.Polymerase.

• mRNA leaves the nucleus and goes to the mRNA leaves the nucleus and goes to the cytoplasm. cytoplasm.

• The mRNA sequence is read in triplets The mRNA sequence is read in triplets (group of 3 bases) called “(group of 3 bases) called “codonscodons.”.”

• Each codon codes for a specific amino acid. Each codon codes for a specific amino acid. (Each codon is like a word in a sentence)(Each codon is like a word in a sentence)

Amino Acid Codon ChartAmino Acid Codon Chart

TranscriptionTranscription

• Transcription requires Transcription requires RNARNA polymerasepolymerase, , an enzyme a lot like DNA polymerasean enzyme a lot like DNA polymerase

• RNA polymerase binds to DNA, separates RNA polymerase binds to DNA, separates the strands, and uses one strand as a the strands, and uses one strand as a template for making mRNA.template for making mRNA.

• RNA polymerase “polymerizes” (links RNA polymerase “polymerizes” (links together) the nucleotides that make up together) the nucleotides that make up mRNAmRNA

RNA

DNA

RNApolymerase

Adenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)

Where to Start?Where to Start?

• RNA polymerase doesn’t randomly RNA polymerase doesn’t randomly bind to DNA.bind to DNA.

• It will only bind to sites known as It will only bind to sites known as promoterspromoters—regions of DNA that —regions of DNA that have specific sequences.have specific sequences.

• Promoters are signals that say Promoters are signals that say “START RNA HERE!”“START RNA HERE!”

• Similar signals also tells transcription Similar signals also tells transcription to stop.to stop.

Start/Stop CodonsStart/Stop Codons

• There are 64 different codons.There are 64 different codons.

• Most code for amino acids.Most code for amino acids.

• There will always be a “Start” codon There will always be a “Start” codon (AUG) at the beginning. It is like (AUG) at the beginning. It is like capitalizing the 1capitalizing the 1stst letter of a sentence. letter of a sentence.

• There will always be a “Stop” codon There will always be a “Stop” codon (UGA, UAA, UAG) at the end. It is like a (UGA, UAA, UAG) at the end. It is like a period at the end of a sentence.period at the end of a sentence.

TranslationTranslation

• tRNA translates the mRNA using tRNA translates the mRNA using “anticodons.”“anticodons.”

• Each tRNA molecule has an anticodon Each tRNA molecule has an anticodon on one end and an amino acid on the on one end and an amino acid on the other.other.

• tRNA transfers the amino acids to the tRNA transfers the amino acids to the ribosome in the correct sequence.ribosome in the correct sequence.

• The ribosome made of rRNA links the The ribosome made of rRNA links the amino acids together to build the amino acids together to build the polypeptide chain or protein.polypeptide chain or protein.

Messenger RNA

Messenger RNA is transcribed in the nucleus.

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.

mRNA Start codon

Ribosome

Methionine

Phenylalanine tRNALysine

Nucleus

mRNA

anticodon

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.

mRNARibosome

Translation direction

Lysine tRNA

tRNA

Ribosome

Growing polypeptide chain

mRNA

Completing the PolypeptideThe process continues until the ribosome reaches one of the three stop codons. The result is a growing polypeptide chain.

Protein Synthesis ReviewProtein Synthesis Review

• DNA carries the information in the form of genes to DNA carries the information in the form of genes to build proteins.build proteins.

• RNA polymerase copies the DNA strand into RNA polymerase copies the DNA strand into messenger RNA (mRNA) which carries the DNA messenger RNA (mRNA) which carries the DNA message.message.

• Transfer RNA (tRNA) reads the message of mRNA, Transfer RNA (tRNA) reads the message of mRNA, gathers the correct amino acids, and delivers them to gathers the correct amino acids, and delivers them to the ribosome for assembly.the ribosome for assembly.

• Ribosomal RNA (rRNA) then takes the amino acids Ribosomal RNA (rRNA) then takes the amino acids from transfer RNA and links them together to make from transfer RNA and links them together to make the protein.the protein.

Remember This!Remember This!

• DNA is like the master blueprint.DNA is like the master blueprint.• RNA is like the blueprint copy the RNA is like the blueprint copy the

workers use.workers use.• The workers are ribosomes.The workers are ribosomes.• Proteins are the finished product.Proteins are the finished product.• Proteins are the keys to almost Proteins are the keys to almost

EVERYTHING that living cells do!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)!!