Molbio: Gene expression and epigenetics

Messenger RNA, Ribosomal RNA, transfer RNA, heteronuclear RNA, small nuclear RNA, micro RNA, short interfering RNA, double stranded RNA, snoRNA, tncRNA, ellipsis

types of RNA (9)

promotor

RNA synthesis begins at the

Initiation, Promoter, Elongation

RNA replication

subscript 2, B, B’

Core enzymes

subscript 2, B, B’o

Haloenzyme

rho

Rho factor

prokaryotic RNA polymerase

core enzyme, haloenzyme, Rho factor

nucleolus

location of type 1 eukaryotic RNA polymerase

nucleoplasm

location of type 2 eukaryotic RNA polymerase

nucleoplasm

location of type 3 eukaryotic RNA polymerase

cytoplasm

location of type Mit eukaryotic RNA polymerase

18S, 5.8S, 28S rRNA

product of type 1 eukaryotic RNA polymerase

mRNA; snRNA

product of type 2 eukaryotic RNA polymerase

tRNA; 5S rRNA

product of type 3 eukaryotic RNA polymerase

MtRNA

product of type MIT eukaryotic RNA polymerase

Cis elements, Trans element

factors that control gene expression

constitutive, inducible

types of gene expression

Constitutive

• Genes that are transcribed continuously

• “housekeeping genes” have products required constantly by the cell

Inducible

Gene products that are required at specific times during the cell cycle or under certain nutritional/environmental conditions

Jacob and Monod (1960s)

discovered the molecular mechanism of inducible gene expression in E. coli

promoter

Site of RNA pol binding

Repressor proteins

trans elements

Operator

Site of R binding

Inducer

binds to repressor protein

Induction, repression, activation

modes of gene regulation in prokaryotes

epigenetics

Non-sequence specific, heritable traits

histone modifications, DNA methylation, Non-coding RNA

epigenetics (3)

histones

Affect the accessibility of DNA to the binding of RNA polymerase and transcription factors

Acetylation, Phosphorylation, Methylation, Ubiquitination, Ribosylation, Glycosylation

Distinct combinations of chemical modifications of histones dictate varying responses:

DNA methylation

occurs mostly on cytosines or adenines (5-methyl cytosine)

Cytosines or adenines

Methylation of DNA occurs mostly on

DNA methyltransferase 1 (DNMT1), DNA methyltransferase (DNMT3)

Two major enzymes methylate eukaryotic DNA:

DNA methyltransferase 1 (D N M T1)

methylates heminethylated DNA

DNA methyltransferase (DNMT3)

methylates unmethylated DNA

Restriction/ modification enzymes

are responsible for methylation of prokaryotic DNA

CpG islands

are sites of methylation in human DNA

Non-coding RNA (ncRNA)

are transcribed and processed but not translated

small ncRNA (micro RNA, short interfering RNA), long ncRNA

ncRNA are classified by size:

long ncRNA

interact with histones and DNA to affect transcription

small ncRNA

interact with mRNA to affect translation

histones and DNA

Long nc RNA interact with __ to affect transcription

mRNA

Small nc RNA interact with ____ to affect translation

Micro RNA (mi RNA)

silences specific genes by hydridizing to the 3' end of the mRNA ad preventing protein synthesis

Small interfering RNA (siRNA)

silence specific genes by promoting degradation of the mRNA target

microRNA, small interfering RNA

Post-transcriptional gene silencing