Nucleic Acids and protein
synthesis
Higher Human Biology
Lesson Aims
• To examine the structure of DNA
• To compare the structure of DNA and RNA
• To discuss the differences and similarities
between mRNA and tRNA
• To examine the role of the nucleus and
nucleolus during RNA synthesis
• To study the synthesis of proteins
• It was Francis Crick and James Watson
who unraveled the DNA molecule.
DNA Molecule
• In 1966 the Genetic code was
discovered.
• Scientists are now able to predict
characteristics by studying DNA. This
leads to genetic engineering, genetic
counseling.
An international team of scientists began
the project to map the human genome.
1990
Gene therapy was used on patients for
the first time.
1994
The FDA approved the first genetically
engineered food -- FlavrSavr tomatoes
engineered for better flavour and shelf life.
1997
Dolly the Sheep - the first adult animal clone.
Dolly the sheep, pictured here with
her first lamb Bonnie
2000
J. Craig Ventor, along with Francis Collins,
jointly announce the sequencing of the entire
human genome.
The Central Dogma
• DNA codes for the
production of DNA
(replication) and of
RNA (transcription).
• RNA codes for the
production of protein
(translation).
The Central Dogma
• Genetic information is stored in a linear
message on nucleic acids. We use a shorthand
notation to write a DNA sequence:
– 5'-AGTCAATGCAAGTTCCATGCAT....
• A gene determine the sequence of amino acids
in proteins. We use a shorthand notation to
write a protein sequence:
NH2-Met-Gln-Cys-Lys-Phe-Met-His.... (or a one
letter code: M Q C K F M H)
DNA Structure - Nucleotide
DNA Structure – Double Helix
Comparison of DNA and RNA
DNA
RNA
Found in
nucleus
Found in
nucleus and
cytoplasm
Double
strands
Single
strand
Bases – A, T, Bases – A, U,
G, C
G, C
Deoxyribose Ribose sugar
sugar
Transcription
Part of chain B sequence.
Uncoiled DNA double helix
which has split exposing
bases
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First stage of protein synthesis
Occurs in the nucleus
Double helix uncoils
Double strands split
DNA strand acts as template for formation of mRNA
(messenger RNA)
Transcription
Single strand
of DNA coding
for Chain B
Strand of
mRNA copied
from DNA
• Free RNA nucleotides in the nucleus base pair with DNA
nucleotides A-T, T-U, G-C, C-G
• Strong bonds form between phosphate group and ribose
sugar of neighbouring RNA nucleotides
• Catalysed by enzyme RNA polymerase
• mRNA moves out of nucleus through nuclear pore
Role of Rough Endoplasmic
Reticulum
• Network of
membranes
• Found in cytoplasm
• Has ribosomes on
surface
• Proteins produced
during translation
pass into ER
Translation
• Second stage of protein synthesis
• Occurs on ribosomes in cytoplasm
• Code on mRNA is used to make protein chain
Translation
Comparison of mRNA and tRNA
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mRNA
Messenger RNA
Made in nucleus
during transcription
Moves to cytoplasm
Codes for protein
Base triplets codons
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tRNA
Transfer RNA
Found in cytoplasm
Involved in
translation
Assembles amino
acids into correct
order for proteins
Anti-codons present
Overview
Overview
Role of Golgi Apparatus
• Found in cytoplasm
• Flattened sacs which
are continually
formed
• Involved in processing
and packaging
proteins
• Vesicles bud off with
processed protein
Secretion
• Also called exocytosis
• Vesicle which has pinched off Golgi apparatus moves
towards cell membrane
• Membrane of vesicle fuses with cell membrane
• Insulin secreted from cell
The Facts You Need To Know
• page 1-2
• from “chromosomes which remain in ….”
• to “the sequence of bases in the DNA…”