Gene ExpressionGene Expression

Chapter 17: From Gene to Protein

The Central Dogma of Biology

The Central Dogma of Biology

DNA (in genes) is a is an essential partner in this process are the links between genotype and

phenotype Gene expression, the process by which DNA directs

protein synthesis, includes 2 stages:

DNA (in genes) is a is an essential partner in this process are the links between genotype and

phenotype Gene expression, the process by which DNA directs

protein synthesis, includes 2 stages:

Relationship between genes and proteins

Relationship between genes and proteins

George Beadle and Edward Tatum exposed

This created mutants that were unable to survive on minimal medium as a result of

Using crosses, they identified three classes of arginine-deficient mutantsEach lacked a different necessary for

synthesizing arginine They developed a

States that

Some proteins aren’t enzymes, so researchers later revised the hypothesis to the

George Beadle and Edward Tatum exposed

This created mutants that were unable to survive on minimal medium as a result of

Using crosses, they identified three classes of arginine-deficient mutantsEach lacked a different necessary for

synthesizing arginine They developed a

States that

Some proteins aren’t enzymes, so researchers later revised the hypothesis to the

Protein synthesisProtein synthesis

RNA is the intermediate between genes and the proteins for which they code

Transcription is the synthesis of

Occurs in the (where the DNA is located)

Produces Translation is the synthesis of a

Occurs on the (cytoplasm)mRNA transcript language is changed to

protein language

RNA is the intermediate between genes and the proteins for which they code

Transcription is the synthesis of

Occurs in the (where the DNA is located)

Produces Translation is the synthesis of a

Occurs on the (cytoplasm)mRNA transcript language is changed to

protein language

Prokaryotes vs Eukaryotes

Prokaryotes vs Eukaryotes

In prokaryotes, mRNA produced by transcription is immediately translated

In a eukaryotes, the separates

transcription from translation A primary transcript is the

Eukaryotic RNA transcripts are modified through

In prokaryotes, mRNA produced by transcription is immediately translated

In a eukaryotes, the separates

transcription from translation A primary transcript is the

Eukaryotic RNA transcripts are modified through

Genetic CodeGenetic Code How are the instructions for assembling amino acids

into proteins encoded into DNA? There are , but there are only

The flow of information from gene to protein is based on a : a series of

Example: AGT on a DNA strand results in the placement of the amino acid serine at the corresponding position of the polypeptide

During transcription, one of the two DNA strands called the template strand provides a

During translation, the

Each codon specifies the addition of

How are the instructions for assembling amino acids into proteins encoded into DNA?

There are , but there are only

The flow of information from gene to protein is based on a : a series of

Example: AGT on a DNA strand results in the placement of the amino acid serine at the corresponding position of the polypeptide

During transcription, one of the two DNA strands called the template strand provides a

During translation, the

Each codon specifies the addition of

CodonsCodons

The genetic code is No codon specifies But there are that code for

the same amino acid Code has start and stop signals All were deciphered by the mid-1960s

61 code for 3 are

Codons must be read in the correct reading frame (correct groupings) in order for the

The genetic code is No codon specifies But there are that code for

the same amino acid Code has start and stop signals All were deciphered by the mid-1960s

61 code for 3 are

Codons must be read in the correct reading frame (correct groupings) in order for the

TranscriptionTranscription

The stretch of DNA that is transcribed is called a

The three stages of transcription:

The stretch of DNA that is transcribed is called a

The three stages of transcription:

InitiationInitiation RNA polymerase binds to

the promoterRNA polymerase is an

enzyme that

and hooks together the The promoter is the

(10-20 bases at a time)Similar to DNA

replication RNA synthesis begins at the

start point on the

RNA polymerase binds to the promoterRNA polymerase is an

enzyme that

and hooks together the The promoter is the

(10-20 bases at a time)Similar to DNA

replication RNA synthesis begins at the

start point on the

Eukaryotic PromotersEukaryotic PromotersPromoters signal the mediate the binding of RNA

polymerase and the initiation of transcriptionThe completed assembly of transcription

factors and RNA polymerase II bound to a promoter is called a

A promoter called a is crucial in forming the initiation complex in eukaryotesTranscription factors bind here and

A gene can be transcribed simultaneously by several RNA polymerases

Promoters signal the mediate the binding of RNA

polymerase and the initiation of transcriptionThe completed assembly of transcription

factors and RNA polymerase II bound to a promoter is called a

A promoter called a is crucial in forming the initiation complex in eukaryotesTranscription factors bind here and

A gene can be transcribed simultaneously by several RNA polymerases

ElongationElongation RNA polymerase moves

It continues to unwind

the DNA and elongate the transcript in the

Double helix as section is passed

This creates a

RNA synthesis follows the same base-pairing rules as DNA, except

RNA polymerase moves

It continues to unwind the DNA and elongate the transcript in the

Double helix as section is passed

This creates a

RNA synthesis follows the same base-pairing rules as DNA, except

TerminationTerminationRNA polymerase reaches the

Signals the of the transcription unit

Involves a RNA transcript is RNA polymerase Transcription Animation

RNA polymerase reaches the Signals the of the transcription

unitInvolves a

RNA transcript is RNA polymerase Transcription Animation

mRNA processingmRNA processing Enzymes in the eukaryote modify pre-mRNA before the

messages are sent to the cytoplasm Each end of a pre-mRNA molecule is modified in a

particular way:The 5 end receives a

This tells ribosome where to begin translatingThe 3 end gets a

Chain of 150-200 Helps to get transcript

Enzymes in the eukaryote modify pre-mRNA before the messages are sent to the cytoplasm

Each end of a pre-mRNA molecule is modified in a particular way:The 5 end receives a

This tells ribosome where to begin translatingThe 3 end gets a

Chain of 150-200 Helps to get transcript

mRNA processingmRNA processing Next the transcript must be edited by Most eukaryotic genes and their RNA transcripts have

long of nucleotides that lie between

The introns must be In some cases, RNA splicing is carried out by

A variety of proteins and several small nuclear ribonucleoproteins (snRNPs) that recognize the splice sites

Next the transcript must be edited by Most eukaryotic genes and their RNA transcripts have

long of nucleotides that lie between

The introns must be In some cases, RNA splicing is carried out by

A variety of proteins and several small nuclear ribonucleoproteins (snRNPs) that recognize the splice sites

RNA as an enzymeRNA as an enzyme

Ribozymes are

3 properties of RNA enable it to function as an enzymeIt can form a 3-D structure

because of its ability

Some bases contain

It may hydrogen-bond with

Ribozymes are

3 properties of RNA enable it to function as an enzymeIt can form a 3-D structure

because of its ability

Some bases contain

It may hydrogen-bond with

Alternative RNA Splicing

Alternative RNA Splicing

Some genes can encode more than one kind of polypeptide, depending on

Such variations are called alternative RNA splicing

Because of alternative splicing, the

Some genes can encode more than one kind of polypeptide, depending on

Such variations are called alternative RNA splicing

Because of alternative splicing, the

Components of Translation

Components of Translation

There are 3 different forms of RNA, each with a specific purpose during translation is a copy of the DNA

recipe, created in transcription together with proteins

forms ribosomes where proteins are made brings an amino acid

to the ribosome to help create the polypeptide

There are 3 different forms of RNA, each with a specific purpose during translation is a copy of the DNA

recipe, created in transcription together with proteins

forms ribosomes where proteins are made brings an amino acid

to the ribosome to help create the polypeptide

tRNAtRNA

A tRNA molecule consists of a that is about

nucleotides longBases to each

otherCloverleaf shape

3’ end picks up the and carries it to ribosome

Amino acid is determined by 3 bases opposite the amino acid called an Anticodons pair with

A tRNA molecule consists of a that is about

nucleotides longBases to each

otherCloverleaf shape

3’ end picks up the and carries it to ribosome

Amino acid is determined by 3 bases opposite the amino acid called an Anticodons pair with

tRNAtRNA Molecules of tRNA are unique

since Accurate translation requires

two steps:1. A correct match between

a , done by the enzyme aminoacyl-tRNA synthetase

2. A correct match between the

Flexible pairing at the third base of a codon is called

and allows some tRNAs to bind to more than one codon

Molecules of tRNA are unique since

Accurate translation requires two steps:1. A correct match between

a , done by the enzyme aminoacyl-tRNA synthetase

2. A correct match between the

Flexible pairing at the third base of a codon is called

and allows some tRNAs to bind to more than one codon

rRNA rRNA Ribosomes consists of

made of RNA & proteinTwo functions

A ribosome has three binding sites for tRNA:The holds the tRNA that carries

the next amino acid to be added to the chainThe holds the tRNA that carries

the growing polypeptide chainThe is where discharged tRNAs

leave the ribosome

Ribosomes consists of made of RNA & protein

Two functions

A ribosome has three binding sites for tRNA:The holds the tRNA that carries

the next amino acid to be added to the chainThe holds the tRNA that carries

the growing polypeptide chainThe is where discharged tRNAs

leave the ribosome

rRNA rRNA Ribosome moves along

mRNA until it reaches

A number of ribosomes can translate a single mRNA simultaneously, forming a

Polyribosomes enable a cell to make

Ribosome moves along mRNA until it reaches

A number of ribosomes can translate a single mRNA simultaneously, forming a

Polyribosomes enable a cell to make

Steps of translationSteps of translation

There are 3 stages of translation:

All three stages require protein “factors” that aid in the translation process

There are 3 stages of translation:

All three stages require protein “factors” that aid in the translation process

Chain InitiationChain Initiation

First, a small ribosomal subunit binds with

Then the small subunit moves along the mRNA until it reaches the

Anticodon of the initiator tRNA will complementary base pair with first codon, which always codes for

Proteins called initiation factors bring in the large subunit that completes the

First, a small ribosomal subunit binds with

Then the small subunit moves along the mRNA until it reaches the

Anticodon of the initiator tRNA will complementary base pair with first codon, which always codes for

Proteins called initiation factors bring in the large subunit that completes the

Chain ElongationChain Elongation

During the elongation stage, amino acids are added

Each addition involves proteins called elongation factors and occurs in 3 steps: (complementary

tRNA comes into the A site) (amino acid

from the tRNA at the P site is attached to the amino acid on the tRNA at the A site)

(mRNA moves the tRNA at the A site to the P site so the next tRNA can go into the P site)

During the elongation stage, amino acids are added

Each addition involves proteins called elongation factors and occurs in 3 steps: (complementary

tRNA comes into the A site) (amino acid

from the tRNA at the P site is attached to the amino acid on the tRNA at the A site)

(mRNA moves the tRNA at the A site to the P site so the next tRNA can go into the P site)

Chain TerminationChain Termination

Occurs when a in the mRNA reaches the A site of the ribosome

The A site accepts a protein called a

is released is released

Occurs when a in the mRNA reaches the A site of the ribosome

The A site accepts a protein called a

is released is released

Translation AnimationsTranslation Animations

Animation 1 http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/

translation.swf

Animation 2 http://carbon.cudenver.edu/~bstith/transla.MOV

Practice http://gslc.genetics.utah.edu/units/basics/transcribe/

Animation 1 http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/

translation.swf

Animation 2 http://carbon.cudenver.edu/~bstith/transla.MOV

Practice http://gslc.genetics.utah.edu/units/basics/transcribe/

Polypeptides vs Proteins

Polypeptides vs Proteins

Often translation is not sufficient to make a

Polypeptide chains are after translation

During and after synthesis, a polypeptide chain spontaneously Remember: A protein’s shape

Some polypeptides are

Other polypeptides come together to form the

Often translation is not sufficient to make a

Polypeptide chains are after translation

During and after synthesis, a polypeptide chain spontaneously Remember: A protein’s shape

Some polypeptides are

Other polypeptides come together to form the

Review QuestionsReview Questions1. Explain the central dogma of biology.2. Define gene expression, including its 2 main parts.3. Explain how Beadle & Tatum’s experiment related genes to

proteins.4. Differentiate between transcription and translation.5. Explain how gene expression differs in prokaryotes and

eukaryotes.6. Define codons and their importance to gene expression.7. Name and describe the 3 stages of transcription.8. Define the roles of the promoter sequence, RNA polymerase,

transcription factors, and the terminator sequence in transcription.9. Describe the 3 main events that occur in mRNA processing.10. Differentiate between introns and exons.11. Define ribozymes.12. Describe alternative RNA splicing.13. Differentiate between mRNA, rRNA, and tRNA.14. Explain the importance of an anticodon to gene expression.15. Name and describe the importance of the 3 sites of the ribosome.16. Name and describe the 3 steps of translation.17. Name 2 main events that occur during chain initiation of

translation.18. Explain the 3 steps of translational elongation.19. Name 3 events that happen during chain termination of

translation.20. Differentiate between polypeptides and proteins.