4: GENETICS - RNA + PROTEIN SYNTHESIS Flashcards
What is protein synthesis?
the production of proteins from info contained within a cell’s DNA
What are the 2 main stages of protien synthesis?
- transcription
- translation
What is mRNA and what does it do?
- messenger RNA
- made during transcription
- carries genetic code from DNA to ribosomes where it is used to make a protein during translation
What is the structure of an mRNA molecule?
a single polynucleotide strand
What are groups of 3 adjacent bases in an mRNA molecule called?
codons
What is tRNA and what does it do?
- transfer RNA
- involved in translation
- carries amino acids that are used to make proteins to the ribosomes
What is the structure of a tRNA molecule?
- single polynucleotide strand folded into a clover shape
- H bonds between specific base pairs hod tRNA in the clover shape
- every tRNA molecule has a specific sequence of 3 bases (anticodon) at 1 end and an amino acid binding site at the other end
Where does transcription take place in eukaryotic cells?
the nucleus
Where does transcription take place in prokaryotic cells?
the cytoplasm
Describe the process of transcription
- RNA polymerase (enzyme) attaches to the DNA double helix at the beginning of a gene
- H bonds between the 2 strands of DNA are broken by DNA helicase attached to the RNA polymerase which separates the 2 strands and the DNA molecule uncoils, exposing some of the bases
- 1 of the strands is used as a template to make an mRNA copy
- RNA polymerase lines up free RNA nucleotides alongside the exposed bases on the template strand
- the free bases are attracted to the exposed bases. complementary base pairing means that mRNA strands end up being a complementary copy of the DNA template
- once the RNA nucleotides have paired up with their complementary bases on the DNA strand, they’re joined together by RNA polymerase, forming an mRNA strand
- RNA polymerase moves along the DNA strand, assembling the mRNA strand
- H bonds between uncoiled strands of DNA reform once the RNA polymerase has passed by and the strands coil back into a double helix
- when RNA polymerase reaches a specific sequence of DNA bases (the stop signal) it stops making mRNA and detaches from the DNA
- in eukaryotes mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome
What is pre-mRNA?
mRNA strand containing introns and exons`
What is splicing?
a process in which introns are removed from the pre-mRNA and and exons are joined together
Does splicing occur in prokaryotic cells/eukaryotic cells/both?
eukaryotic cells only
Why can mRNA be produced directly from DNA in prokaryotes?
there are no introns in prokaryotic DNA
Describe the process of translation?
- mRNA attaches itself to a ribosome and tRNA molecules carry amino acids to it. ATP provides energy needed for the bond between the amino acid and the tRNA molecule to form
- a tRNA molecule (carrying an amino acid) attaches itself to the mRNA by complementary base pairing between the anticodon on the tRNA and the mRNA codon. a second tRNA molecule attaches itself to the next mRNA codon in the same way
- the 2 amino acids attached to the tRNA molecules are joined by a peptide bond
- the 1st tRNA molecule moves away, leaving its amino acid behind
- a 3rd tRNA molecule binds to the next codon on the mRNA. its amino acid binds to the 1st 2 and the 2nd tRNA molecule moves away. this process continues, producing a chain of linked amino acids (a polypeptide chain) until there is a stop signal on the mRNA molecule
- the polypeptide chain then moves away from the ribosome
