BIO122 CH 17

What is the Central Dogma Central dogma: DNA to RNA to protein

Gene Expression: The process by which DNA directs protein synthesis includes two 
stages  

Transcription: synthesis of RNA using information in DNA, produces mRNA, tRNA and rRNA  

Translation: synthesis of a polypeptide (later folded into a protein) using mRNA  

Proteins: are the links between genotype and phenotype 

 

 
What is the genetic code? The information content of genes is in the specific sequence of nucleotides chart of codons that change to amino acid 

What does it mean to say the genetic code is redundant but not 
ambiguous?

The genetic code is redundant (more than one codon specifies a particular amino acid) but not ambiguous (no codon specifies more than one amino acid) 

What does it mean to say the genetic code is universal

the genetic code we have is the same for every other organism on the planet 

 
What are the three steps of transcription? Initiation, Elongation, and Termination

What happens in Initiation of transcription? 

  1. Initiation: promoter (TATA Box) and transcription factors 

All types of RNA (mRNA, rRNA, and tRNA) are made by what?

transcription 

Initiation of Transcription: Transcription factors purpose?

  • Transcription factors mediate the binding of RNA polymerase and the initiation of transcription 

  • Transcription factors work with TATA Box.  

Initiation of Transcription: the name of the promoter in eukaryotes

TATA box  

Initiation of Transcription: promoter’s purpose?

promoter tells DNA polymerase where to attach  

What happens in Elongation of transcription?

As RNA polymerase moves along the DNA, it untwists the double helix, 10 to 20 bases at a time.  

What happens in Termination of transcription?

  • Polyadenylation sequence 

  • Termination occurs when RNA polymerase transcribes sequence of DNA known as a terminator 

  • Differs in bacteria and eukaryotes  

Termination of transcription in bacteria?

Bacteria: Termination at signal  

Termination of transcription in eukaryotes?

Eukaryotes: RNA polymerase II transcribes a particular sequence, and The RNA transcript is released 10–35 nucleotides past this point  

 

 
What is meant by the template strand? How can you determine which strand of DNA is the template strand? 

  • template strand is what I'm going to use to transcribe my RNA; what is used as the template 

  • non template strand the other strand of DNA 

 
In what direction does transcription proceed? 

  • 5’ to 3’ direction 

 
How is transcription initiated? What is needed for this to occur? 

  • For transcription to occur, must have a promotor: the DNA sequence where RNA polymerase attaches which signals the start point

What’s a transcription unit?

The stretch of DNA being transcribed

What is needed for transcription to be terminated to occur?

RNA polymerase transcribes sequence of DNA known as a terminator 

 
What is mRNA processing

Preparing mRNA to leave the nucleus so it can be translated into a polypeptide

Whys mRNA processing needed?

mRNA is threaded through pores in nucleus, so we have to protect it from breaking  

 
What occurs during mRNA processing? 

Addition of a 5' cap, adding a poly-A tail at the 3' end, and Splicing out introns 

mRNA processing: addition of a 5’ cap

The 5’ end receives a modified nucleotide 5’ cap 

mRNA processing: splicing out introns: spliced meaning

the introns are removed, and the exons are joined together, creating an mRNA molecule with a continuous coding sequence 

mRNA processing: splicing out introns occurs before…

mRNA leaves the nucleus

mRNA processing: splicing out introns carried out by what?

RNA splicing carried out by spliceosomes  

mRNA processing: splicing out introns: spliceosomes consist of?

a variety of proteins and ribozymes (small RNA molecules capable of acting like an enzyme 

mRNA processing: splicing out introns: noncoding regions meaning…

Intervening sequences, or introns  

mRNA processing: splicing out introns coded regions meaning…

Coded regions are exons because they are eventually expressed  

 
What type of RNA is needed for translation? 

mRNA 
 

What are the three steps of translation? Initiation, Elongation, and Termination

What happens in Initiation of Translation?

Ribosomes assemble around target mRNA and the start codon 5’ AUG is recognized. 

What happens in Elongation of Translation?

  • Codon recognition*, peptide bond, translocation* 

  • The tRNA transfers an amino acid to the tRNA bound to the next codon, forming a peptide bond between the two amino acids. 

What happens in Termination of Translation?

The ribosome recognizes the stop codon and the polypeptide is released. 

Transcription: where?

Nucleus

Translation: where?

Cytoplasm

Transcription: RNA?

MRNA transcribed from DNA 

Translation: RNA?

TRNA translates mRNA to amino acids using ribosome (made of rRNA) 

Are the steps for Transcription and Translation the same?

Yes, but what happens in each step is different for transcription and translation

How is Initiation different in Translation and Transcription?

Translation: Start Codon 

Transcription: TATA Box

How is Elongation different in Translation and Transcription?

Transcription: RNA Polymerase 

Translation: Codon recognition*, peptide bond, translocation* 

How is Termination different in Translation and Transcription?

Transcription: Polyadenylation sequence 

Translation: Stop Codon 

Transcription: Final Product?

MRNA strand with 5’ cap and poly-A tail 

Translation: Final Product?

Chain of amino acids (primary structure of protein)

What is a codon?

A codon is a very specific sequence of three RNA bases

How is a codon used?

  • Use codon as a code using genetic code(chart) determine what amino acid  

  • Sequence of amino acids is a polypeptide chain 

An anti-codon? 

Anticodon forms complimentary base pairs with mRNA 
 

What role do ribosomes play in translation?

Ribosomes facilitate specific coupling of tRNA anticodons with mRNA codons

Ribosomal structure Translation:

  • Two ribosomal subunits (large and small) are made of proteins and ribosomal RNA (rRNA)  

  • Each ribosome has three binding sites for tRNA: E, P, and A

What is the significance/function of the E, P and A site in a ribosome? 

  1. The P site holds growing polypeptide chain 

  1. The A site carries the next amino acid to be added to the chain  

  1. The E site is the exit site 
     

How is translation initiated? What is needed for this to occur? 

  • A small ribosomal subunit binds with mRNA and an initiator tRNA (anticodon UAC) 

  • The ribosomal subunit moves along the mRNA until it reaches the start codon (AUG) which signals the start of translation  

Translation Initiation factors (proteins) role

bring in the large subunit that completes the translation initiation complex 

 

What are the three steps of elongation in translation?

  • Each addition of amino acids involves proteins called elongation factors  

  1. Codon recognition

  1. Peptide bond formation  

  1. Translocation

Which of the three steps of elongation in translation require energy?

Codon recognition and translocation


In what direction does translation proceed? 

Translation works in the 5’ to 3’ direction of mRNA; meaning anticodons are read in the 3’ to 5’ direction

 

How does translation terminate? What is needed?

Elongation continues until a stop codon (UAA, UAG, UGA) in the mRNA reaches the A-site of the ribosome

What is a release factor? 

When a stop codon is recognized, the A-site accepts a protein called a release factor  

What does a release factor do? Translation: termination

  • This causes the addition of a water molecule instead of an amino acid  

  • The reaction releases the polypeptide, and the translation assembly comes apart  

 
What is a mutation?

Mutation: changes in the genetic material of a cell  

why is it significant? 

Mutations to one or a few nucleotides can affect protein structure and function