BIO 1A03 Test 2 real

one gene-one enzyme hypothesis

each gene contains the information needed to make an enzyme

What did George Beadle and Edward Tatum research?

Relationship between genes and proteins using the Neurospora Crassa

One gene-one enzyme hypothosis (Neuroposa Example)

Neurospora can grow well on minimal medium (simple sugar, vitamins, inorganic salts), and therefore it must have enzymes produced by a certain gene that that transform these materials into amino acids and vitamins needed for growth.

Metabolic pathway of Arginine

Precursor, Ornithine, Citrulline, Arginine

Adrian Srb and Norman Horowitz

Radiation treated neurospora to create mutations in DNA code. They identified three mutants

Medium supplemented with arginine

POSITIVE CONTROL (Growth)

Non-supplemented medium

No Growth

Exceptions to one gene one enzyme hypothesis

More than one protein can be produced from a single gene - post translational modification of proteins allows for the production of diverse proteins with specific roles

What allows of the synthesis of a polypeptide chain during translation?

GTP-dependent factors

Where does the majority of glucose absorption take place?

Microvilli cells of the small intestine

How many amino acids are translated from the insulin gene

110 amino acids

How many chains is a functional insulin protein made of?

2 (alpha and beta)

Alpha chain

21 amino acids

Beta chain

30 amino acids

Preproinsulin

Protein cleaved to become proinsulin which is cleaved to become insulin

How do you get from preproinsulin to proinsulin

Cleavage of the n-terminal signal sequence

Proinsulin to insulin

Undergoes folding, goes from rough ER to Golgi, where cleavage of c-chain occurs

List postranslational modifications

Cleavage, phosphorylation, methylation, acetylation

Phosporylation

The adding of a phospate to a molecule using kinase enzyme

Receptors

Proteins that receive and interpret messages from signalling molecules

dimerization

pairing of two receptor-hormone complexes

glucose transporters

proteins that assist in the transport of glucose molecules across cell membranes

location of translation

cytoplasm

Number of anticodon loops on tRNA

3

Direction of Anticodon

3' to 5'

What is the point of attachment for the amino acid to the tRNA

terminal adenine

aminoacyl-tRNA synthetase

An enzyme that joins each amino acid to the appropriate tRNA.

Once bound to the active site, these enzymes can then catalyze the covalent attachment of a tRNA molecule to its amino acid using the energy from....

ATP hydrolysis

How many codons are there?

64

How many tRNAs are there?

45

tRNA wobble

Accurate base pairing is required only in the first 2 nucleotide positions of an mRNA codon, so codons differing in the 3rd "wobble" position may code for the same tRNA/aa (due to degeneracy of genetic code).

eukaryotic initiation of translation

1. Initiation complex forms near the 5' cap of mRNA

2. Scans DNA until AUG codon is found

Prokaryotic Initiation of Translation

Initiation complexes form at ribosome binding sites called Shine-Dalgarno sequences (few bp upstream of AUG)

polycistronic mRNA

A single molecule of messenger RNA that is formed by the transcription of a group of functionally related genes located next to one another along bacterial DNA.

Factors required for assmbly

Initiation Factors

Delivery of charged tRNA

Elongation factors

Termination

Release factors, driven by GTP hydrolysis

Similarities between prokaryotic and eukaryotic translation

Two ribosomal subunits, the mRNA that requires translation, the charged tRNA methionine and initiation factors that will help with assembling the initiation complex.

Where do amino acids bind on mRNA?

A site

peptidyl-transferase reaction

reaction that bonds each amino acid being added to the growing polypeptide chain though a condensation reaction and peptide bond formation

GTP-bound elongation factors

Causes the deacylated tRNA to move from the P-site to the exit (or E site).

The subsequent aminoacyl-tRNA to enter the A site will then allow for the release of the deacylated tRNA from the E site.

How does termination of translation take place?

a stop codon is reached, GTP-bound release factors bind to A-site and catalyze the hydrolysis of the bond between the terminal amino acid in the polypeptide and the tRNA in the P-site.

What do prokaryotes need to grow

Amino acids, carbs, vitamins, temperature

housekeeping genes

a gene that is transcribed continually because its product is needed at all times and in all cells (structural/ribosomal) proteins

regulated genes

genes whose activity is controlled in response to the needs of a cell or organism

lactose gets broken down into

Glucose and Galactose

What enzyme metabolizes lactose

b-galactosidase

B-galactosidase

enzyme of regulated gene that breaks down lactose when glucose is used up

What did francis Jacob and Jacques Monod conclude?

b-galactosidase is only produced when lactose is present

translational control

gene expression regulated by influencing the interaction of the mRNA transcripts with the ribosome

transcriptional control

control of gene expression by the use of transcription factors, and other proteins, that regulate either the initiation of transcription or the rate at which it occurs

post-translational control

Regulation of gene expression by modification of proteins (e.g., addition of a phosphate group or sugar residues) after translation.

Which control mechanism is the fastest?

Post-translational

Which control mechanism is the slowest

Transcriptional

Which control mechanism is the most efficient

transcriptional (No resources wasted)

Environmental cues in Ecoli

1. Changes in glucose levels

2. Presence of lactose

lactose permease

transports lactose into the cell

Why aren't b-galactosiodase and lactose permiase produced when glucose is available

1. Glucose inhibits

2. Lactose promotes after glucose runs out

Where is b-galactosiodase located

cytoplasm

What does B-galactosidase do?

cleaves lactose into glucose and galactose

What is an operon?

a group of genes that are regulated together in bacterial DNA

operon model

gene expression in bacteria is controlled by single on/off switch (operator) that can control the transcription of the regulated gene

operator

Region of DNA that controls RNA polymerase's access to a set of genes with related functions.

lac operon

a gene system whose operator gene and three structural genes control lactose metabolism in E. coli

Regulatory Sequences in Lac Operon

promoter, operator (lac o)

What gene codes for the repressor protein in lactose gene

lac I gene

What gene codes for lactose permease

lacY gene

What gene codes for Beta galactosidase?

lacZ gene

Is the lac operon negative or positive?

negatively regulated

What shape does the lac repressor protein create when bound to lactose operon?

DNA Loop

How does lactose turn on the lac operon?

It attaches to the repressor, which causes the repressor to fall off the operator. Transcription takes place.

When does cAMP accumulate?

when glucose is scarce

adenylyl cyclase

An enzyme that converts ATP to cAMP in response to an extracellular signal.

Cyclic AMP receptor protein (CRP)

is the activator protein on lac gene

How does the cell use up all the glucose before utilizing lactose

High glucose inhibits production of adenylyl cyclize enzyme therefore inhibiting production of cAMP

negatively regulated transcription

A repressor protein will bind to the operator region of the operon, resulting in the turning off of transcription

> RNA polymerase is no longer able to bind to the promoter region of the operon

positively regulated transcription

A transcriptional activator protein binds to an activator binding site on the DNA

> Activator can be upstream, downstream, or even overlap with the promoter

> Binding of the activator with the DNA allows for the recruitment of RNA polymerase to the promoter and then the initiation of transcription

> Transcription cannot occur if the activator is not present or able to bind to the activator binding site

When are lac operon mRNA levels highest (A,B,C)

After lactose has been used up (top of the graph)

operon

a group of genes that operate together

embryonic stem cells

An undifferentiated cell, taken from an embryo that has potential to give rise to various other cell or tissue types

What causes cell differentiation?

Only specific parts of the DNA are activated into RNA, and certain genes are regulated (transcription factors)

Similarities between transcriptional regulation in prokaryotes and eukaryotes

1) Repressor/activator proteins

2) Both use RNA Polymerase

Difference between transcriptional regulation in prokaryotes and eukaryotes

1) Prokaryotes have operons with one promoter

2) Eukaryotes have genes with their own operators and promoters

Histone

protein molecule around which DNA is tightly coiled in chromatin

chromatin remodeling

the process of chemical changes to the DNA and histones that activate and inactivate gene expression

histone modification

1) Positively charged tails of histone proteins probably interact with negatively charged phosphate of DNA

2) Acetylation of tails weakens their interaction with DNA and may permit some transcription factors to bind to DNA

acetylation of histones

Unwinds DNA, adds actyl group- changes shape = genes turned ON

methylation of histones

hides the transcribing DNA and reduces transcription levels

DNA binding motifs

regions of regulatory proteins which bind to DNA

enhancer sequences

-Can enhance transcription even when located several thousand base pairs from a promoter.

-Enhancer DNA sequences bind transcription factors called enhancer-binding proteins which increase the rate of transcription.

promoter region

A regulatory region a short distance upstream from the 5' end of a transcription start site that acts as the binding site for RNA polymerase. A region of DNA to which RNA polymerase binds in order to initiate transcription.

cis-acting sequences

transcription regulation requires binding of many regulatory factors to specific DNA sequences

What binds to the promoter?

General transcription factors

What binds to enhancers?

transcriptional activator proteins

Silencer regions

Leads to interference of mediator activity which is needed for binding of RNA polymerase and subsequent transcription

mediator complex

A protein complex that acts as an adaptor that interacts with transcription factors bound to regulatory sites and with general initiation factors for RNA polymerase II-mediated transcription.

Hemoglobin protein in adults

2 alpha-globins, 2 beta-globins

hemoglobin in babies

2 alpha and 2 gamma globins

CpG islands

DNA regions rich in C residues adjacent to G residues. Especially abundant in promoters, these regions are where methylation of cytosine usually occurs.

epigenetic mechanisms

May "silence" genes, such as tumor-suppressing genes. Ie, methylation of the promoter region of the gene, a change that prevents transcription and causes gene inactivity.