Transcription and Translation

Question 1

structure + several characteristics of DNA

Answer 1

pics lect 3, slide 7:
double helix structure
- double stranded*
- anti-parallel*
- base pairs form hydrogen bonds in the center*
- phosphate group, sugar backbone, nitrogenous base*
- phosphodiester bond between subunits in chain*
- nitrogenous bases (adenine, thymine, guanine, cytosine)
- H at the right end of sugar group

Question 2

central dogma of molecular biology

Answer 2

DNA –> converted to RNA –> converted to protein

Question 3

DNA vs RNA comparisons

Answer 3

DNA (DeoxyriboNucleic Acid) = (1) usually double-stranded, (2) thymine base, (3) H at the right end of sugar group, (4) deoxyribose sugar and phosphate backbone, (5) self-replicating, (6) long-term storage of genetic info
RNA (RiboNucleic Acid) = (1) usually single-stranded, (2) uracil base, (3) OH at the right end of sugar group, (4) ribose sugar and phosphate backbone, (5) RNA synthesized from DNA, (6) used to transfer the genetic code from the nucleus to the ribosomes to make proteins

Question 4

what is gene expression

Answer 4

the process by which DNA directs protein synthesis

Question 5

types of RNA and what they stand for

Answer 5

mRNA - messenger RNA: encodes amino acid sequence of a polypeptide
tRNA - transfer RNA: brings amino acids to ribosomes during translation
rRNA - ribosomal RNA: with ribosomal proteins, makes up the ribosome, the organelles that translate the mRNA
snRNA - small nuclear RNA: with proteins, forms complexes that are used in RNA processing in eukaryotes (not found in prokaryotes)

Question 6

basic 2 stages of gene expression

Answer 6

transcription: DNA strand serves as template for synthesis of complementary RNA strand
translation: a polypeptide is synthesized, using mRNA as a template
- both stages done in separate places in cell + RNA processing also takes place

Question 7

what are ribosomes made + function

Answer 7

two subunits; made of rRNA and protein + involved in protein synthesis/where translation takes place*

Question 8

stages of transcription**

Answer 8

1. Initiation: RNA polymerase binds to promotor region with help of transcription factors (required) –> with help of promotors, RNA polymerase initiates transcription –> separates DNA strands
2. Elongation: RNA polymerase moves along unwound DNA strand, uses strand as template, and creating complementary mRNA strand (RNA nucleotides added to 3’ end –> read strands from left to right: DNA template: 3’ to 5’, RNA: 5’ to 3’)
3. Termination: RNA polymerase crosses stop (termination) sequence (polyadenylation signal sequence) –> mRNA strand is complete and detaches from DNA

Question 9

what are promoters?

Answer 9

specific sequence of DNA in gene where transcription is initiated (helps RNA polymerase initiate transcription)

Question 10

example of promotor in eukaryotes

Answer 10

TATA box (for transcription initiation)

Question 11

mRNA processing

Answer 11

after transcription –> done because pre-mRNA is not functional, need mature mRNA
3 types of RNA processing nucleus:
1. addition of 5’ cap by capping enzyme
2. addition of 3’ poly-A tail by poly-A polymerase
3. RNA splicing: spliceosomes* (snRNA, “snurps”) remove introns –> exons then joined together

Question 12

introns and exons

Answer 12

introns are non-coding regions on gene and exon is coding region –> introns need to be spliced during mRNA processing to create continuous coding sequence (mature mRNA) –> exons joined together to create final protein

Question 13

what are the building blocks of proteins?

Answer 13

amino acids

Question 14

introns and exons are found in what type of cell?

Answer 14

only in eukaryotes

Question 15

translation

Answer 15

conversion of mRNA into a new protein (building blocks of protein = amino acids)

Question 16

what is a codon?

Answer 16

triplets of nucleotide bases that code for an amino acid

Question 17

tRNA

Answer 17

tRNAs bring amino acids (mRNA sequence) to ribosome
main components:
- amino acid attachment site
- anticodon which base pairs with the codons of the mRNA

Question 18

ribosome binding sites

Answer 18

on top of bottom ribosome subunit: mRNA binding site
3 tRNA binding sites:
- left to right EPA
- 1. P-site: where initiator tRNA-Met binds + carrying polypeptide chain
- 2. A-site: holds tRNA with next amino acid
- 3. E-site (exit): where empty tRNAs leave ribosome

Question 19

stages of translation**

Answer 19

1. Initiation (all pieces come together to form complete ribosome): small ribosome subunit binds to mRNA –> binds to first initiating tRNA binds to P-site –> large ribosomal subunit comes down –> now ready to accept additional tRNAs + building chain
2. Elongation (amino acids added one by one to preceding amino acid chain):
   - a. codon recognition: new tRNA comes into A-site
   - b. peptide bond formation: Met on P-site transferred to A-site and peptide bond forms the 2 amino acids
   - c. translocation: empty tRNA in P-site moved to E-site to leave ribosome –> tRNA with attached peptide chain in A-site moved to P-site
   - keep adding amino acids until polypeptide chain is complete
3. Termination: protein release factor binds to (1 of 3) stop codon* –> new polypeptide release –> bonds broken and everything disassembles

Question 20

how are restriction enzymes named?**

Answer 20

first letter of genus, next 2 letters species, strain designation, then roman numeral which indicated placement of enzyme in organism
- example: EcoR1 –> E. coli, strain RY 13, and first enzyme found in that species