Bio 111 Ch. 12

What is a gene?

A segment of DNA that is copied into RNA and produces a functional product.

What is polyA addition of eukaryotic mRNA during pre-RNA processing?

At the 3' end, most eukaryotic mRNAs have a string of adenine nucleotides referred to as a polyA tail. the tail is aded enzymatically after a pre-mRNA has been completely transcribed. the tail aids in the export of mRNAs from the nucleus and allows it to be more stable and last longer in the cytosol

Transcription

Copying DNA into an RNA molecule of some sort Over 90% of all genes are structural (mRNA-> proteins) Transfer RNA (tRNA) - helps in translation of mRNA into amino acids Ribosomal RNA (rRNA) - part of ribosomes

Eukaryote v. Prokaryote Transcription/Translation

Eukaryotic transcription involves more protein. There are 3 forms of RNA polymerase: II-transcribes mRNA I and III-transcribes nonstructural genes for rRNA & tRNA bacterial mRNA's are translated into polypeptides immediately

What is anticodon of a tRNA? What are charged tRNA?

GGC

RNA processing

In eukaryotes Bacterial mRNAs translated into polypeptides immediately BUT Eukaryotic mRNAs pre-mRNA -> mature mRNA Introns Exons Splicing- removal of introns and connection of exons 7-methyl G cap addition PolyA tail

How does transcription and translation occur in bacterial cells?

Know that the transcription and translation in bacterial cells are coupled and occurs in cytoplasm. In other words, the transcription and translation take place simultaneously. The mRNA gets translated as it is being transcribed

Which enzyme attaches amino acid to a particular tRNA?

aminoacyl-tRNA synthetases catalyze the attachment of amino acids to rTNA molecules-20 types

What is the difference between eukaryotic and bacterial ribosome?

bacterial cells have 1 type of ribosome which translates all mRNAs in the cytoplasm. Their subunts are smaller than eukaryotic ribosomes.Because eukaryotic cells are compartmentalized into organelles, biochemically distinct ribosomes are found in different cellular compartments. the most abundandt type of eukaryotic ribosome functions in the cytosol. many antibiotics can only bind to bacterial cells to stop translation

Start and Stop Codons

codons are groups of 3 nucleotides. the genetic code has 64 different codons Start-AUG Stop-UAA, UAG, UGA-signal the end of translation

mature mRNA

final product following the pre-mRNA

what is the difference between the gene expression in bacteria and eukaryotes in terms of transcription and translation. What is fundamental difference between the two?

in bacteria, transcription and translation occur in the cytoplasm. in eukaryotes, transcription and RNA processing occurs in the nucleus, whereas translation takes place in the cytosol

What are the 3 stages of translation

initiation elongation termination

Splicing

introns are removed from the pre-mRNA and the remaining exons are connected to each other

Beadle and Tatum's experiment using Neurospora Arginine auxotrophs.

like Garrod, hypothesized that genes carry the info to make specific enzymes. they reasoned that a mutation might cause defects in the enzyme required for the synthesis of an essential molecule, such as a vitamin. exposed Neurospora cells to X-rays, which caused mutations to occur, and studied the resulting cells. by plating the cells on growth media with or without vitamins, they were able to identify mutant strains that required vitamins for growth. concluded that a single gene controlled the synthesis of a single enzyme-->one-gene/one-enzyme hypothesis.

What is capping during pre-mRNA processing?

mature mRNAs of eukaryotes have a modified form of guanine covalently attached at the 5' end. Capping occurs while a pre-mRNA is being made by RNA polymerase. They are needed for the proper exit of mRNAs from the nucleus. after the mRNA is in the cytosol, the cap structure helps to prevent mRNA degradation and is recognized by other cap-binding proteins that enable the mRNA to bind to a ribosome for translation

9. What are tRNAs? What is their role in translation?

molecule with 2 functional sites: one site (anticodon) binds to a codon in the mRNA, and a second site is where an appropriate amino acid is attached. Act as carriers of the correct amino acids during translation. Different tRNA molecules encoded by different genes Common features Cloverleaf structure Anticodon Acceptor stem for amino acid binding

What happens when you add or delete bases (nucleotides) to translation products?

mutation occurs that can affect the protein function which could affect the ability of an organism to survive and reproduce.

What is a frame-shift mutation?

mutation that involves the addition or deletion of a number of nucleotides that are not in multiples of 3

What is alkaptonuria?

patients' body accumulate abnormal levels of homogentisic acid. this compound which is bluish-black results in discoloration of the skin and cartilage and causes urine to appear black

structural gene as a transcriptional unit

promoter-signals the beg. of transcription regulatory sequence-site for the binding of regulatory proteins which influence the rate of transcription Transcribed region-part of this region contains the info that specifies an amino acid sequence. Terminator-signals the end of transcription

Transcription factors

proteins that influence the ability of RNA polymerase to transcribe genes.

initiation, elongation, termination

recognition of start site. In bacteria, sigma factor causes RNA polymerase to recognize promoter region RNA polymerase synthesizes RNA after release of sigma factor; open complex 10-15 base pairs long and synthesized 5' to 3'. uracil is switched for thymine and DNA unwinds behind open complex RNA polymerase reaches termination sequence RNA polymerase falls off DNA New RNA molecule is released

What is Garrod's "inborn error of metabolism"

refers to a mutation in a gene that is inherited from one or both parents. He proposed a relationship b/w the inheritance of a mutant gene and a defect in metabolism. if an indvl inherited the mutant gene from both parents, she would not produce any normal enzyme and would be unable to metabolize homogentisic acid.

1. introns 2. extrons

scientists found that the coding sequences within many eukaryotic structural genes are separated by DNA sequences that are transcribed BUT NOT translated into protein 1. intervening sequences that are transcribed but not translated -> removed before export to cytosol (intervening regions that are not expressed b/c they are removed from the mRNA) 2. coding sequence found in mature mRNA (expressed regions)

What is a ribosome?

site where translation takes place large complex made of large and small subunits

Translation

synthesizing a specific polypeptide on a ribosome. a nucleotide sequence in mRNA is "translated" into an amino acid sequence of a polypeptide.

central dogma

the transcription of DNA into mRNA and the translation of mRNA into a polypeptide chain(linear seq. of amino a's)

Why is Beadle and Tatum's hypothesis of "one-gene one- enzyme" now discarded?

this idea is now discarded because the info to make all proteins do not function as enzymes. second, some proteins are composed of 2 or more different polypeptides. third, some genes encode RNAs that are not used to make polypeptides.(some are used to make ribosomes)

How does transcription take place in eukaryotes?

transcription and translation are uncoupled. Transcription takes place in nucleus while translation occurs in the cytoplasm.

Pre-mRNA

transcription initially produces a longer RNA which undergoes certain processing events before it exits the nucleus and becomes mRNA still contains introns with the exons