Lecture 13: Transcription and Translation

What is the Central Dogma?

Journey from DNA to RNA to protein

Why Do Cells Need to Make Proteins?

PERFORM most of the cell’s work

What is Transcription?

Using DNA as a template to SYNTHESIZE (make) RNA

What is the Central Dogma Equation?

DNA → transcription → RNA → translation → protein

What Molecule is Read by Ribosomes to Make Proteins?

RNA (specifically mRNA)

What is the Role of DNA in Transcription?

DNA provides the template for making RNA

What is the “Language” of DNA and RNA?

Nucleic acids

Why Must RNA be Made Before a Protein?

Ribosomes READ mRNA to assemble a protein

What Enzyme Catalyzes Transcription?

RNA polymerase

Where Does Transcription Occur on DNA?

GENES (specific portions of DNA)

Where Does Transcription Occur on Eukaryotes?

Nuclues

Where Does Transcription Occur on Prokaryotes?

Cytoplasm

What do DNA and RNA Nucleotides Contain?

• 5’ Carbon Sugar

  • Ribose or Deoxyribose

  • Attached to nitrogenous base

What Sugar is Found in RNA?

• Ribose

• OH group at 2’ Carbon

What Sugar is Found in DNA?

• Deoxyribose

• H at 2’ Carbon

Where is the Phosphate Group Attached to a DNA/RNA Nucleotide?

5’ Carbon

What is the Key Difference Between Ribose and Deoxyribose?

• Ribose → OH at 2’ Carbon

• Deoxyribose → H at 2’ Carbon

How Many Phosphate Groups Can a Nucleotide Have?

One to three P groups

What are The Nitrogenous Bases in RNA?

• Adenine (A)

• Guanine (G)

• Cytosine (C)

• Uracil (U)

What are The Nitrogenous Bases in DNA?

• Adenine (A)

• Guanine (G)

• Cytosine (C)

• Thymine (T)

What is an NTP?

• Nucleotide Triphosphate

• NUCLEOTIDE with three phosphate groups

What is a dNTP?

• Deoxynucleotide triphopsphate

• DNA NUCLETODIE with three phosphate groups

Is Transcription Similar in Prokaryotes and Eukaryotes?

Yes! (but they occur in different locations)

What Are The Two DNA Strands Involved in Transcription?

• Template strand

• Non-template strand

What is the Template Strand?

DNA strand used as TEMPLATE to make RNA

What it the Non-Template Strand?

DNA strand NOT used as template to make RNA

What Binds to Promoter Sequences to Initiate Transcription?

• Transcription factors

• RNA polymerase

What is the Role of Transcription Factors in Transcription Initiation?

• HELP initiate transcription

• BIND to DNA near promoter

What are Genes?

Regions of DNA read during transcription

Where Does Transcription Begin and End

• BEGIN → promoter sequence

• END → terminator sequence

What is the Direction of RNA Synthesis During Transcription?

5’ to 3’

Can Both DNA Strands Serve as Templates for Transcription?

• Yes!

  • Each gene uses ONLY ONE strand as its template

What Do Transcription Factors Do During Transcription Initiation?

• RECOGNIZE and BIND to promoter region

• RECRUIT (brings) RNA polymerase

• ARE proteins

What is a Promoter?

• SPECIFIC DNA sequence

• BEFORE region to be transcribed

• HELPS recruit RNA polymerase

What is the TATA Box?

Promoter sequence found in some eukaryotes

What Happens When Transcription Begins?

• DNA Unwinds

• RNA Polymerase begins synthesisng RNA

What is the Role of RNA Synthesis During Transcription Initiation?

Synthesizes RNA using DNA as template

What Happens During RNA Transcript Elongation?

• RNA polymerase unwinds DNA

• ADDS RNA nucleotides

Where Does RNA Polymerase Add New RNA Nucleotides?

To the 3’ end (of the growing RNA strand from 5’ to 3’)

How Does RNA Polymerase Match RNA Nucleotides to DNA?

COMPLEMENTARY base pairing (with DNA strand)

When Is an Incoming Ribonucleotide Added During Transcription?

When it correctly base-pairs with the DNA template

What Provides the Energy to Add an RNA Nucleotide?

High-energy phosphate bonds (of incoming ribonucleotide)

What Does the 3′-OH of the Growing RNA Strand Do?

• ATTACKS the incoming nucleotide's phosphate bond

• ALLOWS the RNA strand to grow

What Is Pyrophosphate During Transcription?

• RELEASES two phosphate groups

• WHEN incoming ribonucleotide added to RNA strand

Where Does Transcription Terminate?

Specific termination site (for each gene)

What Often Triggers Transcription Termination?

Formation of an RNA hairpin loop

What Is an RNA Hairpin Loop?

• Structure

• FORMED when bases within same RNA strand pair with each other

What Happens When Transcription Terminates?

• RNA polymerase stops adding ribonucleotides

• RNA transcript is released (no 3’ OH on growing RNA to add to)

Why Does RNA Polymerase Stop When the RNA Separates From the DNA Template?

• RNA-DNA hydrogen bonds disrupted

• RNA polymerase can NO LONGER continue with RNA synthesis

What Holds the Newly Made RNA to the DNA Template During Transcription?

Hydrogen bonds (between complementary bases)

How Is RNA Used Differently in Prokaryotes vs. Eukaryotes?

• PROKARYOTES → RNA us used immediately in translation

• EUKARYOTES → RNA is process before use

Why Do Eukaryotes Process RNA Before Translation?

• TO modify the initial RNA transcript

• INTO mature RNA for translation.

What Are the Three Main RNA Processing Events in Eukaryotes?

• ADDITION of “cap” to 5’ end

• ADDITION of poly A tail” to 3’ end

• RNA splicing

What Is Added to the 5′ End of Eukaryotic RNA

5’ cap

What Is Added to the 3′ End of Eukaryotic RNA?

PolyA tail

What Are the Functions of the 5′ Cap and PolyA Tail?

• STABILIZE RNA

• HELP promote translation

What Are Introns?

RNA sequences REMOVED during RNA splicing

What Are Exons?

RNA sequences JOINED together and retained (in mature mRNA)

What Does RNA Splicing Produce?

• NEW messenger RNA (mRNA)

  • HAS exons and introns

What Happens During RNA Splicing?

• REMOVES introns

• EXONS joined together

What Is a Spliceosome?

• RNA-protein complex

• CARRIES out RNA splicing

What Is Mature mRNA?

• Process RNA

• Introns REMOVED

• READY to be translated into protein

What Is Translation?

SYNTHESIS of polypeptide/protein using mRNA information

Where Does Translation Occur in Eukaryotic Cells?

Cytosol OR endoplasmic reticulum (ER)

What Carries Out Translation?

Ribosomes

What Is the Role of mRNA During Translation?

Provides genetic instructions to build protein

What Is a Polypeptide?

• Chain of amino acids

• FORMS protein or part of protein.

What Are the Three Types of RNA Required for Translation?

• mRNA (messenger RNA

• rRNA (ribosomal RNA)

• tRNA (transfer RNA)

What Is the Function of mRNA During Translation?

SPECIFIES sequence of amino acids in protein

What Is the Function of rRNA?

FORMS structural and functional components of ribosomes

What Is the Function of tRNA?

• LINKS genetic information in mRNA to amino acids

• USED to build a protein

How Are mRNA, rRNA, and tRNA Made?

• MADE by transcription

• FROM specific gene in chromosome

What Is a Codon?

• SEQUENCE of 3 nucleotides

• IN mRNA

• CODES for amino acid or stop signal

How Does the Ribosome Read mRNA During Translation?

Reads mRNA in groups of 3 nucleotides (codons)

What Is the Genetic Code?

RELATIONSHIP between nucleotide sequence (mRNA) and amino acid sequence (protein)

What Does It Mean That the Genetic Code Is a Triplet Code?

Each codon CONSISTS of 3 nucleotides

What Does It Mean That the Genetic Code Has No Ambiguity?

Each codon SPECIFIES only one amino acid or stop signal

What Is the Start Codon and What Does It Code For?

• AUG → Methionine (Met)

• SIGNALS start of translation

What Are the Three Stop Codons?

• UAA, UAG, UGA

• SIGNAL end of translation

What Does It Mean That the Genetic Code Is Non-Overlapping and Continuous?

• Ribosome READS codons one after another

• DOESN’T skip nucleotides or reuse them

What Does It Mean That the Genetic Code Is Highly Conserved?

Genetic code is VERY SIMILAR across most organisms

What Is the Function of tRNA During Translation?

• HELPS read mRNA code

• INSERTS correct amino acid to the ribosome

What Is the Structure of tRNA?

• Short RNA

• FOLDS through internal base pairing

• FORMS specific 2D and 3D structures.

What Does the 2D Structure of tRNA Look Like?

Cruciform (cloverleaf) shape

What Does the 3D Structure of tRNA Look Like?

Upside-down L shape

What Is Attached to the 3′ End of tRNA?

(Specific) amino acid

What Is the Anticodon on tRNA?

• SEQUENCE of 3 nucleotides

• PAIRS with complementary codon on mRNA

How Does the tRNA Anticodon Pair With an mRNA Codon?

Complementary, antiparallel BASE PAIRING

What Enzyme Attaches the Correct Amino Acid to a tRNA?

Aminoacyl-tRNA synthetase (tRNA ligase)

How Are Amino Acids Attached to the Correct tRNAs?

• tRNA ligase RECOGNIZES specific amino acids and tRNAs

• ATTACHES them together

What Provides the Energy to Attach an Amino Acid to tRNA?

ATP

What Is an Aminoacyl-tRNA?

• tRNA

• SPECIFIC amino acid attached

• READY to be used in translation

What Is the Function of Ribosomes?

• COORDINATE translation

• SYNTHESIZE proteins.

What Are Ribosomes Made Of?

• 60% RNA

• 40% protein

What Are the Three Functional Sites of a Ribosome?

• A site

• P site

• E site

What Happens at the A Site of a Ribosome?

ACCEPTS aminoacyl-tRNA (tRNA carrying an amino acid)

What Happens at the P Site of a Ribosome?

Peptide bonds FORM between amino acids as protein chain grows

What Happens at the E Site of a Ribosome?

Empty tRNA EXITS the ribosome.

What Are the Three Stages of Translation?

• Initiation

• Elongation

• Termination

Where Does the Initiation Complex Form in Eukaryotes?

5′ cap of mRNA