From Genes to Proteins Flashcards by Ailish Kemble

What is Transcription?

The synthesis of messenger RNA (mRNA) using DNA as a template. RNA polymerase uses DNA as a template to produce pre-mRNA

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What is translation?

The production of proteins from mature mRNA, builds the protein encoded by the original gene

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What are promoter elements in eukaryotes?

TATA BOX

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How is transcription started?

The short run of T & A bases can vary slightly from gene to gene and is probably the best characterised promoter element (TATA box)

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Why are T & As used?

they form the lowest energy base pairs so are easiest to unwind

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What is the first step in transcription?

INITIATION

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Where does RNA polymerase bind?

Binds to DNA upstream (5’) of the gene at a promoter sequence

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What Co factors does RNA polymerase use and why?

cofactors= general transcription factors
TFIID recognises the TATA box and ensures that the correct start site is used

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What does alteration of promoter strength cause?

Can have deleterious effects upon a cell, often resulting in disease

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What is the second step in transcription?

ELONGATION

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What happens during elongation?

The DNA double helix unwinds, RNA polymerase reads template strand and adds complementary nucleotides

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What is the final step in transcription?

TERMINATION

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What stops transcription?

Terminator sequences are found close to the ends of noncoding sequences

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What stops transcription in Pol I genes

termination factor
through a mechanism similar to rho-dependent termination in bacteria (rRNA)

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What stops transcription in pol II genes?

can continue for hundreds of or thousands of nucelotides beyond the end of the noncoding sequence (mRNA)

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What stops transcription of Pol III genes

ends after transcribing a termination sequence that includes a polyuracil stretch (tRNA)

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What is splicing?

removal of intronic sequences from the pre-mRNA. Coding regions (Exonic sequences) are spliced together. Num of exons varies. forms mature mRNA

How does splicing occur?

2 transesterification reactions

What are the steps in splicing?

1st reaction is the free 2’- hydroxy group
the 3’ hydroxy group of the 5’ exon attacks and cleaves the phosphodiester linkage at the 3’ splice site
The products are spliced mRNA product and excised intron

What is the excised intron called?

lariat product

What is self splicing?

The intron itself folds into a specific conformation without the involvement of other RNA or protein

What is alternative splicing?

the process by which a given gene is spliced into more than one type of mRNA molecule

Why is splicing important

Fundamental role in cellular metabolism
Protein diversity
Regulation of gene and protein content
Evolution of new and improved proteins
Key to cancer pathology

How is protein diversity brought about?

Changes in the number & sequence of exons and introns present in the RNA sequence

What is a frameshift mutation?

The addition (insertion) or loss (deletion) of a base would result in a change of reading frame and proteins with altered function

What can frameshift mutation cause?

Array of diseases

Where does translation occur?

RIBOSOME

What is a ribosome comprised of?

2 subunits, large and small, each subunit exists separated in the cytoplasm, but join together on the mRNA molecule

What are tRNA molecules

Adaptor molecules, one end can read the triplet code on mRNA via complementary base pairing & the other attaches to a specific amino acid

What does rRNA do?

catalyses the attachment of each new amino acid to the growing chain forms the ribosome

What is the first step in translation?

Initiation - Translation begins with formation of a complex on the mRNA Three initiation factor proteins bind to small subunit of the ribosome The preinitiation complex and a methionine carrying tRNA then bind to mRNA forming an initiation complex

What are the 3 initiation factor proteins?

IF1, IF2, IF3

What is the second step in translation?

ELONGATION - Ribosome moves along mRNA in a 5-3 direction, elongation factor G is required for TRANSLOCATION - Methionine- carrying tRNA starts out in the middle slot of the ribosome

What acts as the energy source for translation?

Guanosine triphosphate acts as energy source On binding of the tRNA- amino acid complex GTP= guanosine diphosphate

How are peptide bonds formed between amino acids?

peptidyl transferase activity

What is the 3rd step in translation?

TERMINATION - Three stop codons UAA, UAG, UGA

How are stop codons recognised?

By release factors which fit into the P site When a ribosome reaches the stop codon it dissociates and protein is released

What is the genetic code?

64 triplets called codons Each codon except 3 codes for one of the 20 amino acids Some aa encoded for by more than one codon

What is a triplet?

Sequence of three nucleotides found on a strand of DNA or RNA to code for a specific amino acid

What are the 3 stop codons?

UAA (U ARE ANNOYING) UGA (U GO AWAY) UAG (U ARE GONE)

What is the Methionine codon (Met)

AUG (A universal go)

What is the wobble hypthesis?

Suggests that specificity for the base at the 3' end of the condon is not always observed explains why multiple codons can code for one amino acid