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RNA
•Ribonucleic acid
•single stranded
•also made of nucleotides
RNA nucleotides
•Sugar (ribose)
•Phosphate
•nitrogenous base
•adenine
•cytosine
•guanine
•uracil
Types of RNA
•mRNA: messenger RNA, carries
the DNA code out of the nucleus to
the ribosome
•tRNA: transfer RNA, carries amino
acids to the ribosome
•rRNA: ribosomal RNA, part of the
ribosome
Transcription (making RNA)
1. DNA unzips
2. one strand of DNA acts as a template
3. RNA polymerase reads the DNA bases
3’ to 5’
4. RNA nucleotides are placed across from
the complimentary DNA bases
5. RNA separates from DNA
6. DNA zips back up
mRNA processing
1. Methylated guanine cap
added to 5’ end
2. Poly-A tail added to 3’ end of
mRNA
3. Introns (non-coding RNA) are
removed
4. Exons (coding RNA) are
spliced together
mRNA Processing
• 5’ cap
• 3’ AAAAAAA “poly-A” tail
• Introns removed, exons spliced
together
http://www.arabidopsis.org/servlets/sv?action=
accession&type=gene&id=2204897&chr=1
Click on this link and click
on the sequence ruler to
view genetic sequence
with introns, exons etc.
Protein Synthesis
or
How to Make Your
Own Proteins
•mRNA: messenger RNA - singlestranded, brings the DNA message out of
the nucleus.
•tRNA: transfer RNA – single-stranded
but looped around to be shaped like a “t”.
brings an amino acid to a ribosome to
build a protein.
•Transcription: making mRNA. RNA
polymerase (enzyme) reads one strand of
unzipped DNA, and makes mRNA using
the order of the DNA bases.
•mRNA leaves the nucleus through the
nuclear pores. In the cytoplasm, mRNA
is read by ribosomes.
Translation
Translation: making proteins from the
mRNA code.
Translation: making proteins from the
mRNA code.
•mRNA enters a ribosome.
•One tRNA molecule brings one amino acid to
the ribosome.
•Another tRNA brings another amino acid and
the 2 amino acids form a peptide bond.
•The first tRNA leaves the ribosome and the 2nd
tRNA shifts over.
•This growing polypeptide chain will become a
protein.
•The order of amino acids is vital to the
formation of proteins.
•How does the ribosome and tRNA know
the order of amino acids?
•It’s in the order of bases on the mRNA.
•Every 3 bases on mRNA is a codon.
•A codon specifies an amino acid.
•There are also codons which mean stop
making the protein and a codon which
means start.
•The 3 codon bases of mRNA correspond to
3 bases on tRNA called the anticodon.
•tRNA molecules have different anticodons
which identifies which amino acid it carries
to the ribosome.