RNA and Protein RNA and Protein SynthesisSynthesis

Section 12–3Section 12–3This section describes RNA and its This section describes RNA and its

role in transcription and role in transcription and translation.translation.

The Structure of RNA The Structure of RNA

List the three main differences between List the three main differences between RNA and DNA.RNA and DNA.

1.1. RNA has ribose sugar instead of RNA has ribose sugar instead of deoxyribose.deoxyribose.

2.2. RNA is generally single-stranded, instead RNA is generally single-stranded, instead of double-stranded.of double-stranded.

3.3.RNA contains uracil in place of thymine.RNA contains uracil in place of thymine.

Purpose of RNA Purpose of RNA

Is the following sentence true or false?Is the following sentence true or false?

►RNA is like a disposable copy of a DNA RNA is like a disposable copy of a DNA segment.segment.

►TrueTrue

What is the importance of the cell’s What is the importance of the cell’s ability to copy a single DNA sequence ability to copy a single DNA sequence into RNA?into RNA?

► It makes it possible for a single gene to It makes it possible for a single gene to produce large numbers of RNA produce large numbers of RNA molecules.molecules.

Types of RNA Types of RNA

What is the one job in which most What is the one job in which most RNA molecules are involved? RNA molecules are involved?

►Most are involved inMost are involved inprotein synthesis.protein synthesis.

Types of RNATypes of RNA

►Complete the compare-and-contrast Complete the compare-and-contrast table about the types of RNA.table about the types of RNA.

Type FunctionType Function

• Carries copies of the instructions for assembling Carries copies of the instructions for assembling amino acids from DNA to the rest of the cell.amino acids from DNA to the rest of the cell.

• Ribosomal RNA is a part of ribosomes.Ribosomal RNA is a part of ribosomes.

• Transfer RNA Transfers each amino acid to the Transfer RNA Transfers each amino acid to the ribosome to help assembleribosome to help assembleproteinsproteins

Transcription Transcription

Circle the letter of each sentence that is true Circle the letter of each sentence that is true about transcription.about transcription.

• b. b. RNA polymerase uses one strand of DNA RNA polymerase uses one strand of DNA as a template to assemble nucleotides intoas a template to assemble nucleotides intoa strand of RNA.a strand of RNA.

• c. c. RNA polymerase binds only to DNA RNA polymerase binds only to DNA promoters, which have specific base promoters, which have specific base sequences.sequences.

RNA Editing RNA Editing

►Many RNA molecules from eukaryotic Many RNA molecules from eukaryotic genes have sections, called _____, genes have sections, called _____, edited out of them before they become edited out of them before they become functional. The remaining pieces, functional. The remaining pieces, called, _________are spliced together.called, _________are spliced together.

► IntronsIntrons►ExonsExons

RNA Editing RNA Editing

Is the following sentence true or false?Is the following sentence true or false?► RNA editing occurs in the cytoplasm RNA editing occurs in the cytoplasm

of the cell.of the cell.

►FalseFalse

RNA Editing RNA Editing

What are two explanations for why some What are two explanations for why some RNA molecules are cut and spliced?RNA molecules are cut and spliced?

► It makes it possible for a single gene to It makes it possible for a single gene to produce several different forms of RNA.produce several different forms of RNA.

► It may play a role in evolution, making it It may play a role in evolution, making it possible for small changes in DNA to have possible for small changes in DNA to have dramaticdramatic effects in gene expression.effects in gene expression.

The Genetic Code The Genetic Code

Proteins are made by joining ________into Proteins are made by joining ________into long chains called polypeptides.long chains called polypeptides.

►Amino acidsAmino acids

The Genetic CodeThe Genetic Code

►How can only four bases in RNA carry How can only four bases in RNA carry instructions for 20 different amino instructions for 20 different amino acids?acids?

►The genetic code is read three letters The genetic code is read three letters at a time, so that each “word” of the at a time, so that each “word” of the coded message is three bases long.coded message is three bases long.

The Genetic CodeThe Genetic Code

What is a codon?What is a codon?

► It consists of three consecutive It consists of three consecutive nucleotides that specify a single amino nucleotides that specify a single amino acid that is to be added to a acid that is to be added to a polypeptide.polypeptide.

The Genetic CodeThe Genetic Code

Circle the letter of the number of Circle the letter of the number of possible three-base codons.possible three-base codons.

• 44• 1212

c. c. 64 64

d. d. 128128

The Genetic CodeThe Genetic Code

Is the following sentence true or Is the following sentence true or false? false?

• All amino acids are specified by only All amino acids are specified by only one codon.one codon.

►FalseFalse

The Genetic CodeThe Genetic Code

Circle the letter of the codon that serves Circle the letter of the codon that serves as the “start” codon for protein as the “start” codon for protein synthesis.synthesis.

a.UGA a.UGA

b.UAA b.UAA

c.c. UAG UAG

d. d. AUGAUG

Translation Translation

What occurs during the process of What occurs during the process of translation? translation?

►The cell uses information from The cell uses information from messenger RNA to produce proteins.messenger RNA to produce proteins.

Where does translation take Where does translation take place?place?

►Translation takes place on the Translation takes place on the ribosomes.ribosomes.

Circle the letter of each Circle the letter of each sentence that is true about sentence that is true about

translation.translation.► Before translation occurs, messenger RNA is Before translation occurs, messenger RNA is

transcribed from DNA in the nucleus.transcribed from DNA in the nucleus.

► It is the job of transfer RNA to bring the It is the job of transfer RNA to bring the proper amino acid into the ribosome to be proper amino acid into the ribosome to be attached to the growing peptide chain.attached to the growing peptide chain.

►When the ribosome reaches a stop codon, it When the ribosome reaches a stop codon, it releases the newly formed polypeptide and releases the newly formed polypeptide and the mRNA molecule.the mRNA molecule.

What is an anticodon? What is an anticodon?

►The three bases on a tRNA molecule The three bases on a tRNA molecule that are complementary to one of the that are complementary to one of the mRNA codons.mRNA codons.

The Roles of RNA and DNA The Roles of RNA and DNA

Match the roles with the molecules.Match the roles with the molecules.

RolesRoles

► Master plan Master plan - DNA - DNA

► Goes to the ribosomes in the cytoplasmGoes to the ribosomes in the cytoplasm - RNA - RNA

► BlueprintBlueprint – RNA – RNA

► Remains in the nucleus Remains in the nucleus - DNA- DNA

Genes and Proteins Genes and Proteins

►Many proteins are_____, which catalyze Many proteins are_____, which catalyze and regulate chemical reactions.and regulate chemical reactions.

►EnzymesEnzymes

Is the following sentence true Is the following sentence true or false? or false?

Genes are the keys to almost everything Genes are the keys to almost everything that living cells do.that living cells do.

falsefalse

Translation Four Major Steps Translation Four Major Steps

►A. Messenger RNA is transcribed in A. Messenger RNA is transcribed in the nucleus then enters the cytoplasm the nucleus then enters the cytoplasm and attaches to an ribosome.and attaches to an ribosome.

►B. Transfer RNA translation begins at B. Transfer RNA translation begins at AUG, the start codon. Each anti-AUG, the start codon. Each anti-codon of tRNA complements a codon codon of tRNA complements a codon of mRNA and binds a specific amino of mRNA and binds a specific amino acid.acid.

Translation Four Major Steps Translation Four Major Steps cont.cont.

►C. The polypeptide “assembly line” as C. The polypeptide “assembly line” as the codons bind amino acids the the codons bind amino acids the ribosome joins them together forming ribosome joins them together forming long chains of amino acids.long chains of amino acids.

►D. Completing the Polypeptide the D. Completing the Polypeptide the process continues until one of three process continues until one of three stop codons is reached.stop codons is reached.