DNA and RNA

Question 1

DNA polymerase general info

Answer 1

♣ Reads the parent strand in the 3’ to 5’ direction, but synthesizes in the 5’-3’ direction
♣ Creates antiparallel daughter strand
Adds nucleotides to the exposed 3’ end of the parent strand

Question 2

what does monoistronic mRNA mean?

Answer 2

• this means one mRNA strand codes for one polypeptide/protein strand

Question 3

tRNA general info?

Answer 3

♣ small RNA molecule found in the cytoplasm
♣ brings amino acids to the ribosome
♣ one end of the structure contains a 3-nucleotide sequence called the anticodon which is complementary to 3-nucleotides (the codon) in the mRNA
• the other end is a site of attachment for the corresponding amino acid
♣ each amino acids has its own aminoacyl-tRNA synthetase which catalyzes the attachment of the aminoacid to the tRNA

Question 4

rRNA general info

Answer 4

♣ a structural components of ribosomes
♣ most abundant of all rRNA
♣ mRNA passes through two subunits of rRNA structure and is translated to amino acids
synthesized in the nucleolus

Question 5

describe transcription

Answer 5

♣ the initial step of transcription occurs when RNA polymerase binds to DNA at the promoter region
• this is a short DNA sequence found upstream from the site where transcription of a specific RNA is going to take place
• in humans, it is commonly a TATA box
♣ various transcription factors then help RNA polymerase bind to the DNA molecule and initiate transcription
• very similar to replication
• RNA polymerase recruits complementary mRNAs at the “transcription fork” after DNA has been opened by DNA helicase and topoisomerase
o RNA polymerase also has the same polarity as DNA polymerase
♣ After transcription is complete mRNA undergoes post-transcriptional processing
• RNA that has not yet been processed is called hetero-nuclear RNA (hnRNA)
o It contains extra nucleotides that are not necessary in translation
♣ Referred to as introns
• Exons in contrasts are necessary to make the proteins
• Introns are spliced out by the spliceosome
A guanine cap and poly-A tail are added to the ends of the mRNA to provide protection from enzyme degradation as it enters the cytoplasm

Question 6

describe translation

Answer 6

♣ mRNA codons are converted to amino acids
♣ occurs in the cytoplasm
♣ involves tRNA, mRNA, amino acids, ribosomes (rRNA+protein), and other proteins
• can all be divided into distinct stages
o initiation
♣ begins when ribosome binds to mRNA near its 5’ end
♣ ribosome scans mRNA until it binds to a start codon (AUG)
♣ initiator aminoacyl-tRNA (met-tRNA—anticodon 3’-UAC-5’) base pairs with the start codon
o elongation
♣ hydrogen bonds forms between the mRNA codon and the anticodon on the tRNA in the A site of the ribosome
♣ a peptide bond is formed between the amino acid in the P-site (Met) and the incoming on in the A site
♣ after peptide bond formation the ribosome carries an uncharged tRNA in the P-site and a peptidyl-tRNA in the A site
o translocation
♣ cycle is completed by translocation
♣ ribosome advances three nucleotides along the mRNA in the 5’ to 3’ direction
♣ during this the uncharged tRNA from the P site is expelled and the peptidyl-tRNA from the A site moves to the P site
o termination
♣ happens when a stop codon arrives in the A site of the ribosome
• UAA, UAG, or UGA
♣ Frequently, several ribosomes translate a single mRNA molecule
• This forms a structure known as a polyribosome
• After translation is finished, the protein is released and assumes its native conformation
o Determined by the sequence of amino acids (primary structure)
Polypeptide chain can form intramolecular and intermolecular cross-bridges with disulfide bonds

Question 7

ribosome binding sites for tRNA

Answer 7

♣ A
• Aminoacyl-tRNA binding site or arrival site binds the incoming tRNA
♣ P
• Peptidyl-tRNA binding site where the tRNA donates its amino acid to the growing peptide chain
♣ E
Exit site where the tRNA is expelled from after it has donating its amino acid