Genetics Ch 13 Transcription

Amanita phalloides

a poisonous mushroom called the death cap. consumption of this mushroom leads to gastrointestinal symptoms such as ab pain, cramping, vomiting, diarrhea then liver cells die causing permanent liver damage

alpha amanitin

the mushrooms contain this protein which consists of a short peptide of 8 amino acids that form a circular loop. alpha amanitin is a potent inhibitor of RNA polymerase II

what does the death cap inhibit

RNA polymerase II which is responsible for transcribing protein-encoding genes in eukaryotes. the alpha amanitin prevents the RNA polymerase from moving across the DNA template. RNA synthesis slows from a normal speed to only a few nucleotides per minute

what is the job of RNA Polymerase II

to bind to genes and synthesize RNA molecule complementary to DNA template strands by adding one nucleotide at a time to the growing RNA chain.

what are the long term effects of ingesting alpha amanitin

the RNA polymerase II won't transcribe enough, protein synthesis will slow and the required function stops causing cell death. The toxin accumulates in the liver killing off liver cells. A transplant is nearly crucial for survival

what is the first step in the central dogma pathway

to transfer from DNA the genotype to protein which is the phenotype. The central dogma is essentially the transfer of information from DNA to RNA to Protein

what does transcription need in order to occur

required RNA nucleotides, a DNA template and a number or protein components

Life's 2 basic function

organisms must be able to store and faithfully transmit genetic information through reproduction. Secondly the must have the ability to catalyze reactions

ribozymes

catalytic RNA molecules that have the ability to cut out parts of their own sequence connect certain RNA molecules, replicate others, and even catalyze the formation of peptide bonds between amino acids

structure of RNA

a polymer consists of nucleotides joined together via phosphodiester bonds.

differences between RNA structure and DNA structure

RNA consists of Ribose whereas, DNA consists of deoxyribose. RNA molecules have a free 2 prime carbon atom on the ribose sugar. RNA is more unstable than DNA because DNA lacks a free hydroxyl group. RNA has uracil instead of thymine

secondary structures of RNA

hairpin loops or stem loops

when two regions within one RNA molecule pair up the strands in the regions are antiparallel with pairing between cytosine and gaunine and between uracil and adenine

hair pin loops

how is secondary structure determined

by the base sequence of the nucleotide strand. RNA can assume different structures

Ribosomal RNA

rRNA and ribosomal protein subunits make up the ribosome the site of protein assembly

messenger RNA

mRNA carries the coding instructions for polypeptide chains from DNA to a ribosome. after attaching to the ribosome an mRNA molecule specifics the sequence of amino acids in a polypeptide chain and provides a template for joining amino acids

pre mRNAs

large precursor molecules: these are the immediate products of transcription in eukaryotes. pre mRNAs are modified extensively before become mRNA and exiting the nucleus for translation to become a protein

do bacterial cells posses pre mRNA

no, in bacterial cells since there is no nucleus transcription and translation occurs at the same time

similarities between DNA and RNA

both composed of nucleotides, have adenine, guanine and cytosine, nucleotides are joined by phosphodiester bonds

what is the function of ribosomal RNA

it is located in the cytoplasm and makes up the structural and functional components of the ribosome

what is the function of mRNA

located in the nucleus until it is mature and can be put into the cytoplasm. these carry the genetic code for proteins

tRNA

located in the cytoplasm which helps to incorporate amino acids into the polypeptide chain

small nuclear RNA (snRNA)

located in the nucleus of eukaryotes, which process pre-mRNA

small nucleolar RNA or snoRNA

located in the nucleus of eukaryotes and helps in the processing and assembly of pre-mRNA

microRNA or miRNA

located in the nucleus and cytoplasm of eukaryotes which inhibits the translation of mRNA

small interferring RNA siRNA

located in the nucleus and cytoplasm of eukaryotes which trigger the degradation of other RNA molecules

piwi interacting RNA

located in the nucleus and cytoplasm of eukaryotes which suppresses the transcription of transposable elements in reproductive cells

CRISPR RNA

occurs in prokaryotes and assists in the destruction of foreign DNA

small nuclear ribonucleoproteins

small nuclear RNAs which binds with small protein subunits

which RNAs carry out interference

small interfering RNAs and microRNAs

True or false all cellular RNAs are synthesized from DNA templates

true this occurs during transcription

Is transcription a highly selective process

Yes

Transcription requires 3 major components

1. A DNA template
2. Raw materials needed to build a new RNA molecule
3. The transcription apparatus consisting of the proteins necessary to catalyze RNA synthesis

Transcription unit

A stretch of DNA that encodes an RNA molecule and the sequences necessary for transcription

Promoter

A DNA sequence that the transcription apparatus recognizes binds to

What does the promoter do

It determines the transcription start site

RNA coding region

A sequence of DNA nucleotides that are transcribed into an RNA molecule

Terminator

A sequence of nucleotides that signals where transcription should end

When does transcription stop

When the terminator sequence has been copied into RNA

RNA polymerase

Carries out all of the essential steps for transcription with the help of accessory proteins that join and leave the polymerase

In bacterial RNA polymerase the core enzyme consists of

5 subunits two copies of alpha, a beta, a single copy of beta prime, and a single omega

How many polymerases do bacteria cells typically have

1 type of RNA polymerase which catalyzes all the classes of bacterial RNA

Bacterial RNA polymerases

...

Sigma factor

Controls the binding of RNA polymerase to the promoter

What happens if sigma is not present

Then the DNA polymerase would initiate transcription at a random point along the DNA

Holo enzyme

When sigma associate with the core enzyme the structure is called this type of enzyme

How many polymerases does a normal eukaryote have

3

Types of RNA polymerases found in eukaryotes

DNA polymerase 1 2 and 3

RNA polymerase 1

Transcribes ribosomal RNA

RNA polymerase 2

Transcribes pre mRNAs

RNA polymerase 3

Transcribes other small RNA molecules such as tRNA, small r RNA some miRNAS and snRNA

What type of polymerases are found in plants

Polymerase 4 and 5

RNA polymerase 4 and 5

Transcribe nucleotides that play a role in DNA methylation and chromatic structure

Three stages of transcription

1. Initiation
2. Elongation
3. Termination

Initiation

In which the tenacity ion apparatus assembles on the promoter and begins the synthesis of RNA

Elongation

DNA is threaded through RNA polymerase. the polymerase unwinds the DNA and adds new nucleotides, 1 at a time to the 3 prime end of the growing RNA strand

Termination

The recognition of the end of the transcription unit and the separation of the RNA molecule from the DNA

Initiation requires these steps to be done

Promoter recognition
Formation of the transcription bubble
Creation of the first bonds between RNTPS
Escape of transcription apparatus from the promoter

Consensus sequences

Short stretches of common nucleotides

What does it mean when a consensus sequences is present

That the sequence is associated with an important function

Most commonly encountered consensus sequence found in almost all bacterial promoters

-10 consensus sequence often written as Tatat

Common bacterial promoters consensus sequences

-10 and -35