Biology study guide 3: Gene Control

regulation of gene expression

Transcription and Translation

it is through transcription and translation that we see how the genetic information of an organism serves as a code for the manufacturing of everything within that organism

Transcription

the DNA within a gene codes for an mRNA which then undergoes post transcriptional modification (each end gets a special cap tacked on

Translation

the mRNA a ribosome and many tRNA work together to produce a polypeptide

steps to express a gene

transcription

exon slicing

mRNA leaves nucleus

mRNA hooks to ribosomes

translation

in order to transcribe what must attach itself upstream on the template strand to a region called the promoter region?

RNA polymerase

Operon like lac operon

gene needed infrequently

signal turn gene on

otherwise gene is repressed

a protein blocks the promoter site

Operon like trp operon

gene needed most of the time

signal turns gene off

gene product may be signal

feedback loop

differences between the lac and trp operons

lac operon:

• signal is lactose

• gene for making lactase

• signal causes repressor to fall off DNA

• example of a gene thats need infrequently

trp operon:

• signal is tryptophan (an important amino acid)

• gene for making protein to make trp

• signal causes repressor to attach to DNA

• example of a gene needed most of the time

what are two other ways to keep RNA polymerase from binding to DNA?

cytosine methylation

binding to histone

more likely to happen in eukaryote organisms

cytosine methylation

cytosines next to guanines in the promoter region of a gene can be methylated which changes the shape of the region such that RNA polymerase cannot bind to it

DNA tightly bound around histones cannot be what?

TRANSLATED

SNURPS

• crucial complexes of RNA and protein that play a vital role in RNA splicing

• controlling the number and types of snurps you will control how fast introns are cut and the exons are spliced together

• if you want the product made quickly with a lot of copies you need a lot of snurps