Genetics Exam 4

Stuff for the 4th exam plus some previous flashcards

Initiation Bacterial Component: fMET-tRNA

Initiator tRNA

Initiation Bacterial Component: IF1

Blocks A site

Initiation Bacterial Component: IF2

Entry of initiator tRNA

Initiation Bacterial Component: IF3

Blocks association of large subunit (E site)

Elongation Bacterial Component: EF-Tu

Delivers aminoacyl tRNA

Elongation Bacterial Component: EF-G

Translocates ribosome

Termination Bacterial Component: RF1

Recognizes UAA and UAG stop codons

Termination Bacterial Component: RF2

Recognizes UAA and UGA stop codons

Termination Bacterial Component: RF3

Stimulates peptid release

Shine-Dalgarno Sequence

16s rRNA is complementary to a sequence in the 5’ UTR of mRNA

Anticodon

Triplet sequence complementary to codon

Amino Acid tRNA Synthetases

Load tRNAs with their proper amino acids

20 of them - one for each tRNA

Charged tRNA

tRNAs with amino acids

Ribosomes

Molecular factories that brings together mRNA and tRNA in translation, comprised of large and small subunit

Prokaryotic Subunit Numbers

Large - 23S and 5S

Small - 16S

Eukaryotic Subunit Numbers

Large - 28S, 5.8S, and 5S

Small - 18S

rRNA Function

Catalyze most of the steps in translation (not the ribosomal proteins)

A Site

Binds incoming charged tRNA

P Site

tRNA binds growing peptide chain

E Site

Contains deacylated tRNA ready for exit

Decoding Center

Ensures proper tRNA is accepted into A site

Composed of rRNA

Peptidyltransferase Center

Located in large subunit, forms new peptide bonds (for growing polypeptide chain)

Composed of rRNA

Initiation

Adds the first aminoacyl-tRNA in the P site, which is charged with methionine (added by inhibitor rRNA called fMet)

How are proteins modified after translation?

Chemical groups, amino acid modifications, cleavage, or addition of complex molecules

Kinases

Enzymes that catalyze phosphorylation

Phosphorylation

Activates signaling cascade that ultimately leads to expression of genes

Positive Regulation

Activator is involved in recruiting polymerase, causes gene expression

Negative Regulation

Repressor prevents recruitment of polymerase, prevents gene expression (unless effector is bound)

Allosteric Effector

Molecule that binds (such as sugar or allolactose), also called inducers

DNA-Binding Domain

Binds DNA in regulatory proteins

Allosteric Site

Bound by allosteric effector to change proteins shape

Lac Regulator Circuit: O

Non-coding region between promotor and start point of transcription, called the operator

Lac Structural Genes (Z, Y, A)

Encode enzymes for the metabolism of lactose

β-Galactosidase

Modifies lactose so it can be metabolized, breaks it down into galactose, glucose, and allolactose, encoded by lacZ

Permease

Transports lactose into cell, encoded by lacY

Transacetylase

Performs other functions, encoded by lacA

Coordinately Controlled Genes

All transcribed on a single transcript, same regulatory regions and promotor

Operon

Set of adjacent genes whose mRNA is synthesized in one piece, plus the adjacent regulatory cites

Lac Operon

Operon required for the transport and metabolism of lactose, only transcribed in the presence of lactose

Allosteric Transition

When allolactose binds repressor

Induction

Relief of repression

Partial Diploids

When different versions (mutants and non mutants) of the lac operon were present on plasmids and in the bacterial genome

Cis Acting

May only act on adjacent genes on the same chromosome

O^c

Constitutive operator, may not be bound by repressor

When on F’ plasmid with Y^-, Y⁺ may be induced

Cis Acting

Trans Acting

May affect genes located on other chromosomes

cAMP (Cyclic AMP)

Binds CAP protein, which when bound activates transcription by binding to P

Only present when glucose is low

CAP Protein

Activates transcription when bound by cAMP

What does high glucose equate to for cAMP?

Low cAMP

What happens if glucose is low and lactose is high?

CAP binds to cAMP and binds to P to activate transcription, repressor is bound by allosteric effector

Maximum transcription

What happens if glucose is high and lactose is low?

CAP does not bind to cAMP or P, repressor is bound to O

Minimum transcription

Arabinose Operon

Another metabolic operon under dual control

AraC Protein

An activator when bound by arabinose sugar, repressor when arabinose is absent

Trp Operon

Five genes for synthesis of tryptophan amino acid

Trp Repressor (TrpR)

Represses transcription when tryptophan is present, causes attenuation (reduction of amount)

Leader Sequence of 5’ UTR

Accomplishes attenuation, part of the transcript