Protein Synthesis Flashcards
What is a gene
Sequence of bases on a DNA molecule that codes for a sequence of amino acids in a polypeptide chain
What is the genome
The complete set of genetic information in an organism
What are the two stages of protein synthesis and a brief description
Transcription: occurs in nucleus and is where copy of the gene coding for the required protein is made (mRNA)
Translation: amino acids are brought to the ribosome by tRNA which have complementary anticodon for the codon on mRNA
Three differences between RNA and DNA
-RNA is a single stranded polynucleotide while DNA is double stranded
-RNA contains ribose sugar rather than deoxyribose sugar
-uracil replaces thymine in RNA
What occurs during transcription
-enzyme RNA polymerase attaches to DNA causing H bonds between paired bases to break and DNA to unwind
-the sequence on one of the strands is transcribed to make mRNA molecule with same base sequence as DNA coding strand
-complementary RNA nucleotides align themselves into position with template DNA strand and phosphodiester bonds form to produce mRNA molecule
-mRNA leaves nucleus through pore in nuclear envelope and DNA zips up
What occurs during translation
-mRNA attaches to ribosome in cytoplasm
-first codon exposed on ribosome is always start codon which the tRNA carrying complementary anticodon for binds to
-ribosome moves along mRNA strand to expose next codon
-tRNA with anticodon complementary to this next codon brings next amino acid
-ribosome holds mRNA and tRNA in place while peptide bonds form between the amino acids
-translation continues until stop codon is reached which no tRNAs have complementary anticodon for so no amino acid is transferred
-completed polypeptide chain dissociated from ribosome
Structure of a tRNA molecule(transfer RNA)
-at one end is a three base sequence(anticodon) which is complementary to the mRNA codon for a particular amino acid
-at opposite end is a binding site for an amino acid
-within cytoplasm free amino acids become attached to the correct tRNA molcules
What is mRNA and why is it made
-messenger RNA
-sequence of bases with same sequence as DNA sense strand needed to make required protein
-made as it is small enough to leave the nucleus to attach to a ribosome in the cytoplasm
How many bases codes for one amino acid and what is this called
-three bases codes for one amino acid, called a codon
Why is the genetic code degenerate
There are more codon codes than amino acids so more than one codon can code for the same amino acid
