Chapter 10 Gene Expression and Regulationlemastm/Teaching/BI102/Chapter 10 - Central...1 Chapter 10 Gene Expression and Regulation Chapter 10: Gene Expression / Regulation HOW? DNA

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Chapter 10

Gene Expression and Regulation

Chapter 10: Gene Expression / Regulation

HOW?

DNA contains information but is unable to carry out actions

Fact 1:

Proteins are the “workhorses” but contain no information

Fact 2:

Information in DNA must be linked with proteins

THUS

Substrate 1 Substrate 2 Substrate 3

Enzyme

A

Enzyme

B

Gene A Gene B

Beadle & Tatum: Bread mold experiments (1940s)

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Figure 10.1 – Audesirk2 & Byers

Generally, one gene codes

for one protein (polypeptide)

How does information travel from DNA to ribosomes?

Structural Differences between RNA and DNA (See Table 10.1):

1) RNA is single-stranded

2) RNA has ribose sugar in backbone (DNA = deoxyribose)


Answer: RNA (ribonucleic acid)


3) RNA has base Uracil instead of Thymine (A U)

Types of RNA:

Messenger RNA (mRNA)

Carries code from DNA

to ribosomes

Ribosomal RNA (rRNA)

Combines with proteins

to form ribosomes

Transfer RNA (tRNA)

Carries appropriate amino

acids to ribosomesFigure 10.2 – Audesirk2 & Byers

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DNA RNA ProteinTranscription

Nucleus

Translation

Cytoplasm


Central Dogma of Biology:


S O S

Most organisms synthesize 20 unique amino acids

A T

G C= 4

AA TA CA GA

AT TT CT GT

AC TC CC GC

AG TG CG GG

= 16

How many possible three-base sequences (e.g., AAA) are there?


The Genetic Code: The “Language” of Life

Answer: 64

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The genetic code is a triplet code:

• Three bases (called a codon) code for 1 amino acid

• More than 1 codon exists for most amino acids (see Table 10.3)

G C G A A G A G G G C A

Alanine Lysine Arginine Alanine

• Punctuation codons (start / stop) exist in genetic code

• Start = AUG

A U G

START

U A G

STOP

• Stop = UAG, UAA, UGA


The Genetic Code: The “Language” of Life


Nucleus

Translation

Cytoplasm




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Transcription (DNA RNA):

• RNA Polymerase binds to promoter region of gene

Step 1: Initiation

Promoter BodyTermination

Signal

GENET A C

• Different version of RNA polymerase synthesizes each RNA type

Transcription produces a single strand of RNA that is

complementary to one strand of DNA


Non-coding region; protein binding sites

Step 2: Elongation

• RNA Polymerase “unwinds” DNA; synthesizes complementary copy

• Base pair rules apply except uracil replaces thymine

A T C G A A A T C G C G A G G T DNA

U A G C U U U A G C G C U C C A RNA


Transcription:Initiation

Elongation


Strand which is transcribed

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• RNA Polymerase reaches termination signal

Step 3: Termination

Promoter BodyTermination

Signal

GENET A C

Transcription produces a single strand of RNA that is

complementary to one strand of DNA


• RNA detaches from RNA Polymerase

• RNA Polymerase detaches from DNA

• DNA zips back up




Multiple RNA polymerase can transcribe a single gene at the same time


The transcription of genes into RNA is selective:

1) Only certain cells transcribe certain genes

• Insulin (hormone) Pancreas

2) Only one strand of DNA (template strand) is copied

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Nucleus

Translation

Cytoplasm




Translation (RNA Protein):


Step 1: mRNA processed in nucleus

• Exons = Coding segments

• Introns = Non-coding segments

Importance:

A) Multiple proteins from single gene

B) Quick / efficient protein evolution

Step 2: mRNA enters cytoplasm

• Exits nucleus via nuclear pores

Step 3: mRNA binds to ribosome (protein factories)

Composed of rRNA and proteins

• Composed of two (2) sub-units:

Small Sub-unit

Binds mRNA and part of tRNA

Large Sub-unit

Binds part of tRNA; contains catalytic site

Figure 10.2 / 10.7 – Audesirk2 & Byers

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Step 4: tRNA delivers first amino acid to ribosome

• tRNA contains three bases (anticodon) that

form base pairs with mRNA codon

U A C Anticodon

MethionineAmino

Acid

• tRNA has correct amino acid attached for

the mRNA codon (61 unique tRNAs)

Large

Sub-unit

U A C

Met

Small Sub-unit

A U G A A G G C A U C U U A G



Step 5: Elongation of protein

• The next tRNA with proper anticodon binds

to mRNA

Large

Sub-unit

U A C

Met

Small Sub-unit

A U G A A G G C A U C U U A GU U C

Lys

• Catalytic site joins amino acids together (peptide bond)

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to mRNA


• 1st tRNA leaves and ribosome moves down one spot

Large

Sub-unitMet

Small Sub-unit


U U C

Lys

U A C





to mRNA


• 1st tRNA leaves and ribosome moves down one spot

Large

Sub-unitMet

Small Sub-unit


U U C

Lys

U A C

• Cycle repeated

C G U

Ala

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Step 6: Termination of protein

• Process continues until stop codon is reached

• Finished protein is released from ribosome

Small Sub-unit


Met Lys Ala

A G A

Ser




• Process continues until stop codon is reached


Small Sub-unit


Met Lys Ala

A G A

Ser

• Sub-units of ribosome separate from mRNA

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•• Process continues until stop codon is reached


Small Sub-unit


Met Lys Ala Ser

• Sub-units of ribosome separate from mRNA

Transcription / Translation Review:

Chapter 10: Gene Expression / RegulationFigure 10.9 – Audesirk2 & Byers

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Once Again - Mistakes Happen...

Types of Mutations:

1) Point Mutation: A pair of bases is incorrectly matched

Mutation:

Changes in the sequence of bases in DNA

A T A T A T

T A T C T A


Possible outcomes of a point mutation (active gene):

1) Protein is unchanged (codes for same amino acid)

• CTC and CTT still code for leucine

2) New protein equivalent to original protein

• Replace hydrophobic AA with hydrophobic AA (neutral mutation)

3) Protein structure is changed (problem causing – e.g., sickle cell anemia)

4) Protein function destroyed due to stop codon insertion

• AAG codes of amino acid; ATG is a stop codon

Once Again - Mistakes Happen...

Types of Mutations:


3) Deletion Mutation: One or more nucleotide pairs are deleted from

a gene

A T A A T

T A T T A ??

A T A T A TT A T C A T

GA

Mutation:


2) Insertion Mutation: One or more nucleotide pairs are inserted into

a gene

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Once Again - Mistakes Happen...Mutation:



Mutations provide the raw material for evolution...

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Regulation of Genes Occur Across Central Dogma:

1) Rate of transcription controlled:

A) Regulatory proteins

• Assist / block binding of RNA polymerase

B) Chromosome condensation (tightly packed areas)

• RNA polymerase can’t access regions

C) Chromosome inactivity (XX vs. XY chromosomes)


Proper regulation of gene expression crucial for survival

For Example:

30,000 genes in human genome

• Individual cells express small fraction of genes

• Gene expression changes over time

• Some genes never exptressed

Barr Body: Inactive X chromosome in females

• Random during development for which X chromosome inactivates


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Regulation of Genes Occur Across Central Dogma:

1) Rate of transcription controlled


Proper regulation of gene expression crucial for survival

For Example:

30,000 genes in human genome

• Individual cells express small fraction of genes

• Gene expression changes over time

• Some genes never exptressed

2) Genes may produce different protein products

3) Rate of translation controlled (linked to mRNA stability)

4) Protein requires activation modifications

5) Life span of protein controlled

Gene Regulation:

Chapter 10: Gene Expression / RegulationFigure 10.11 – Audesirk2 & Byers

Chapter 10 Gene Expression and Regulationlemastm/Teaching/BI102/Chapter 10 - Central...1 Chapter 10 Gene Expression and Regulation Chapter 10: Gene Expression / Regulation HOW? DNA

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