bio 105 - dna transcription

Transcription

synthesis of an RNA molecule from a DNA template. Process of copying a gene into a complementary mRNA strand.

Transcript

mRNA that specifies the amino acid sequence of a polypeptide

Translation

Process by which a ribosome synthesizes a specific polypeptide using an mRNA template

Central Dogma in Eukaryotes

DNA -> pre-mRNA -> mRNA -> Protein

RNA processing/modification

Modification of RNA primary transcripts, including splicing out of introns, joining together of exons, and alteration of the 5' and 3' ends. Simply, pre-mRNA is processed into mature mRNA.

Some genes don't encode polypeptides. What is the final functional product of these genes?

non-coding RNAS like rRNA and tRNAs

Genes

Instructions for building different proteins are encoded in these sections of DNA. Unit of DNA that code for a functional product.

Gene expression

Pattern of when and where genes are turned on or turned off.

Only some genes are expressed in each cell, at different levels, at different times, thus different cells end up with different...

Proteins (different proteomes).

Coding/transcribed region

part of a gene that contains the coded information for making a polypeptide chain (specifies an amino acid sequence).

What is the functional product of a coding region?

A protein

What is the first step needed to access the information stored in DNA?

Transcription

Promoter

specific region of a gene where RNA polymerase can bind and begin transcription. Signals the beginning of transcription.

Terminator

A special sequence of nucleotides in DNA that marks the end of a gene. It signals RNA polymerase to release the newly made RNA molecule, which then departs from the gene.

Regulatory sequence

Site for the binding of regulatory proteins

Regulatory proteins

Influence the rate of transcription.

What does it mean to say that a gene is expressed?

The gene serves as instructions to make the RNA and then the protein.

Given the template and coding strands, what would the mRNA transcript be? Coding strand : 5'-AATGTAC-3' Template strand : 3'-TTACATG-5'

mRNA transcript : 5'-AAUGUAC-3' (same as CODING strand, but change T to U).

RNA polymerase

enzyme that links together the growing chain of RNA nucleotides during transcription using a DNA strand as a template

Transcription factors

A regulatory protein that binds to DNA and affects transcription of specific genes.

Initiation (transcription)

Transcription factor (sigma factor) binds to a gene's promoter and directs RNA polymerase to bind. Ends with the DNA strands open.

elongation (transcription)

RNA polymerase slides along DNA and synthesizes a complementary mRNA in the 5' to 3' direction from the template strand of DNA

Termination (transcription)

RNA polymerase reaches the terminator sequence and releases from the DNA

Transcription preinitiation complex

A large complex of proteins that is necessary for the transcription of protein-coding genes in eukaryotes, helps position RNA polymerase II over gene transcription start sites, denatures the DNA, and positions the DNA in the RNA polymerase II active site for transcription. Includes protein complex (mediator), general transcription factors, and rna polymerase ii.

What does RNA polymerase require to be present at the promoter in order to initiate transcription?

General transcription factors

TATA box

A DNA sequence in eukaryotic promoters crucial in forming the transcription initiation complex. A common transcription start sequence.

Exons

Coding segments of eukaryotic DNA. Get expressed.

Introns

Noncoding segments of nucleic acid that lie between coding sequences.

Splicing

Removal of introns from pre-mRNA before translation

Why is the addition of caps and tails important?

The addition of caps and tails are imports for sorting mRNAs to the cytosol and for their stability.

spliceosome

A large complex made up of proteins and RNA molecules that splices RNA by interacting with the ends of an RNA intron, releasing the intron and joining the two adjacent exons.

Alternative splicing

Splicing of introns in a pre-mRNA that occurs in different ways, leading to different mRNAs that code for different proteins or protein isoforms. Increases the diversity of proteins.

Coding strand vs template strand

Template strand is the actual strand of DNA from which mRNA is transcribed, so it is complementary to the mRNA. The Coding strand is the complementary strand of DNA to the template strand, so it will actually have the same code as the mRNA, except the Us will still be Ts because its DNA