DNA Chapter 7.4 Flashcards
Transcription
Uses a DNA template to create RNA.
. Transcription produces an RNA copy of one gene
.the cells uses the information from RNA and not the DNA directly to make each protein.
Transcription vs DNA replication ( the 2 main differences
Complementary base pairings underlies transcription just as it does DNA replication. They resemble except for:
- The product of transcription is RNA , not DNA
- Transcription copies just one gene from DNA strand, rather than copying both strands of an entire chromosome.
In Transcriptiion, RNA nucleotides base binds with
exposed complementary bases on the template strand ( which is the strand in the DNA molecule that is actually copied to RNA
Template Strand
The strand in the Dna molecule that is actually copied to RNA
The 3 Steps of Transcription
- Initiation
- Elongation
- Termination
Initiation
- Enzymes unzip The DNA double helix, exposing the template strand.
- RNA POLYMERASE ( the enzyme that builds an Rna chain) binds to the PROMOTER (A DNA sequence that signals the gene’s start)
RNA POLYMERASE
the enzyme that builds an Rna chain
PROMOTER
A DNA sequence that signals the gene’s start
Elongation
RNA polymerase moves along the DNA template strand in a 3’ to 5’ direction, adding nucleotides only to the 3’-end of the growing RNA molecule. ( the creating of the copy of the DNA template: the copy: mRNA )
Termination
- A TERMINATOR sequence signals the end of the gene.
- Upon reaching the terminator sequence, the RNA POLYMERASE enzyme separates from the DNA template and releases the newly synthesized RNA. ( mRNA)
- The DNA molecule resumes its usual double helix shape
What happens to the RNA molecule as it is synthesized
It curls into a 3 dimensional shape dictated by complementary base pairing within the molecule
What does the final shape of RNA determines
whether the RNA functions as mRNA, rRNA, OR tRNA.
. What happens during each stage of transcription
The steps of transcription are initiation, elongation of the RNA molecule, and termination. During initiation, enzymes unzip the DNA and RNA polymerase binds. During elongation, RNA polymerase “reads” the DNA strand and adds complementary nucleotides to the growing RNA strand. During termination, synthesis of the RNA molecule ends and the DNA molecule reforms.
Where in the cell does transcription occur
Transcription occurs in the nucleus.
What is the role of RNA polymerase in transcription?
RNA polymerase uses the DNA template to bind additional RNA bases into the growing chain of RNA being transcribed.
What are the roles of the promoter and terminator sequences in transcription
The promoter signals the start of a gene, and the terminator signals the end of a gene. RNA polymerase recognizes the promoter and terminator, so it starts and stops transcription at the correct positions.
How is mRNA modified before it leaves the nucleus of a eukaryotic cell
Before it leaves the nucleus of a eukaryotic cell, mRNA is altered in the following ways:
- a cap is added to the 5’ end of the mRNA molecule;
- a poly A tail is added to the 3’ end;
- introns are removed and exons are spliced together.
The definition of gene has expanded how
Originally a gene was defined as any stretch of DNA that encodes one protein
. It has now been expanded to include any section of DNA that is transcribed ( protein or RNA as all types of RNA are transcribed not just mRNA)
Gene expression means
Production of either a functional RNA molecule or a protein.
Difference in prokaryotic and eukaryotic cells in transcription/ translation process
In prokaryotic cells ribosomes may begin translating mRNA to a protein before transcription is complete.
In eukaryotic cells the presence of the neuclear membrane prevents mRNA from being transcribed and translated simultaneously.
mRNA is usually altered before leaving the nucleus to be translated
What is a 5’ cap and a poly A tail
What are their purpose
After transcription a CAP ( a short sequence of Modified Nucleotides) is added to the 5' end of a mRna molecule.
Poly A tail: 100-200 adenines are added at the 3’ end.
Together they enhance translation by helping ribosomes attach to mRNA molecule
What are their purpose of the a 5’ cap and a poly A tail
Together they enhance translation by helping ribosomes attach to mRNA molecule
After transcription what two additional steps are done before the mature mRna exists the nucleus
- 5’ cap and Poly A tail is added
2. Introns are removed( leaving exons)
What does the length of the poly A tail determine
How long an m RNA last before being degraded
What is intron short for
Intragenic regions ( within gene)
Introns
Are portions of the mRNA that are not copied and are removed by catalytic RNAs and proteins before translation
The average Exon is how long
100-300 nucleotide long
Exons
The remaining portions once the introns are removed. They are spliced together to form a mature
mRNA
This is what leaves the nucleus to be translated
What are their purpose of the a 5’ cap and a poly A tail
Together they enhance translation by helping ribosomes attach to mRNA molecule
prokaryotic vs. Eukaryotic : how quickly can ribosomes begin translating mRNA
In Bacteria and archaea, ribosomes may begin translating mRNA to a protein before transcription is even complete
Eukaryotes: 1.The presence of the nuclear membrane prevents one mRNA from being simultaneously transcribed
2. In eukaryote cells mRNA is altered before it leaves the nucleus to be translated
