Cell Bio- Transcription

What is a gene?

A region of DNA whose final product is either a polypeptide or an RNA molecule

The sequence of nucleotides in the DNA encodes the information for making a protein

What is gene expression?

The process by which DNA directs protein synthesis

Where does gene expression occur?

Transcription and translation

What is transcription?

The synthesis of DNA under the direction of DNA

Produces: mRNA, tRNA, rRNA

What is translation?

The synthesis of a polypeptide under the direction of mRNA

Occurs on ribosomes

What are the three types of RNA?

Messenger RNA (mRNA), Ribosomal RNA (rRNA), and Transfer RNA (tRNA)

What is Messenger RNA?

A temporary copy of a gene that encodes for proteins

What is Ribosomal RNA?

Part of the ribosome (protein synthesis machinery)

What is Transfer RNA?

Transfers the amino acid to the messenger RNA on the ribosome to decode the mRNA

What is the Central Dogma?

Information flow in a cell follows a defined order and is one-way:

DNA —> RNA —> protein

According to the Central Dogma, Transcription:

DNA —> RNA

According to the Central Dogma, Translation:

RNA —> protein

Who was the first to suggest that inherited diseases were due to inborn errors of metabolism?

Archibald Garrod, 1902

What did Archibald Garrod suggest?

Genes dictate phenotypes, by making enzymes that catalyze chemical reactions

What did Archibald Garrod think?

Genetic diseases were due to a lacking critical enzyme made by a hereditary factor

What was Beadle and Tatum’s hypothesis?

“One gene-one enzyme”

What was Beadle and Tatum experiment (1941)?

To determine if and how genes control known biochemical reactions

Mutated bread mold

What was Beadle and Tatum conclusion?

Each mutant had a mutation in a single gene which encoded a different enzyme and discovered genes act by regulation definite chemical events

What was Beadle and Tatum hypothesis revised to?

“One gene-one polypeptide”

Prokaryotes:

Transcription and translation occurs in the cytoplasm

Translation begins before transcription ends

Eukaryotes:

RNA is made and processed in the nucleus

Translation occurs in the cytoplasm

What is RNA synthesis in transcription?

Catalyzed by RNA polymerase

Unwinds DNA, likes RNA nucleotides together using DNA as a template

Rewinds DNA back together

What strands does DNA have?

A sense strand and antisense strand

What is a sense strand?

In DNA has the same sequence and orientation as mRNA

What is an antisense strand?

Used as the template for RNA transcription and is the complement of mRNA

What is a promoter?

The region of DNA where RNA polymerase binds to start transcription

What is a terminator?

DNA sequence that signals the end of RNA synthesis

What is a primary transcript?

The initial copy of RNA from DNA

What are the stages of RNA transcription?

Initiation, elongation, and termination

What is initiation?

RNA polymerase binds the promoter and unwinds DNA

What is elongation?

RNA pol moves downstream, unwinding DNA, and adding ribonucleotides to the 3’ end of RNA
DNA is rewound behind the RNA pol

What is termination?

Reach the terminator, RNA pol falls off, RNA is released

What is the initiation of transcription (Euk)?

Eukaryotes use transcription factor proteins to help RNA pol bind the promoter