FOR GRADE 12
WHAT IS RNA
> RNA is made up of:
Ribose sugar (a pentose sugar with 5
A nitrogenous base; e.g. Purines (Adenine and
Guanine) and Pyrimidines (Cytosine and
RNA exists largely as single nucleotide chains
in living cells.
> The RNA strand is made up of alternating
molecules of ribose sugar and phosphate.
> The nitrogen bases are attached to the
sugar molecules in the strand and ’stick out’
laterally as in DNA.
> A sugar, a nitrogenous base and a
phosphate together form a ribonucleotide.
> An RNA molecule is a polymer of
> Single strand RNA nucleotides.
> A polynucleotide strand synthesized
according to the code of the DNA.
> It carries the code in base triplet (codon)
form, from the DNA to the ribosomes.
> Found in the nucleus of the cell.
> A single RNA strand folded in the shape of a
> It carries a specific amino acid on one end
and transfers it to the ribosomes.
> Has an anticodon on the other end; the
anticodon base-pairs with a complementary
codon on mRNA.
> Found in the cytoplasm of the cell.
The two ribosomal subunits (large and small)
are made of proteins and ribosomal RNA
The single-stranded molecule of rRNA is
variously folded and twisted upon itself in
certain regions forming a secondary structure.
Constitutes 50% of a ribosome.
Help to bond mRNA to protein of the ribosome.
Found in the ribosomes in the cytoplasm of the
> PROTEIN SYNTHESIS CONSIST OF 2
The 3 stages of transcription:
> RNA-polymerase attaches to the beginning
of the DNA code called the promotor.
> It unwinds the DNA molecule and breaks
the weak hydrogen bonds between the
complementary strands – a “bubble forms”
> The one strand now acts as a template for
the formation of the mRNA strand.
> Free nucleotides in the nucleus bonds to the
complementary bases of the DNA template
strand. (Uracil replaces Thymine in mRNA)
> More free nucleotides bond to their
complementary bases, to elongate the
mRNA strand, until the entire code has
> The mRNA will detach from the DNA
> The RNA polymerase detaches and starts
all over again at a different location where
> Now the pre-mRNA strand has to undergo
a modification and RNA splicing before it can
leave the nucleus
> A cell translates an mRNA message into
WHAT IS NEEDED TO DO THIS?
> mRNA (Carries the code)
> tRNA (pick up amino acid and
takes it to the mRNA
> Amino acid (connect to form
> Ribosome (Location for protein
THE THREE STAGES OF
> Small ribosomal subunit binds with mRNA
Small subunit moves along mRNA until it
reach the start codon (AUG)
> The matching anti-codon of the tRNA
(with amino acid Methionine)bonds with
the start codon.
> Add the large subunit which completes the
translation initiation complex.
> More tRNA anticodons attach to mRNA
> The amino acids attached to the tRNA’s
attach to one another by means of peptide
> Amino acids form a long polypeptide chain.
tRNA releases amino acid to pick up more
> Termination occurs when a stop codon in
the mRNA reaches the A site of the
> The A site accepts a protein called a
> The release factor causes the addition of a
water molecule instead of an amino acid.
> This reaction releases the polypeptide, &
the translation assembly then comes apart