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RNA and Proteins
Shu-Ping Lin, Ph.D.
Instit te of Biomedical Engineering
Institute
Enginee ing
E-mail: splin@dragon.nchu.edu.tw
Website: http://web.nchu.edu.tw/pweb/users/splin/
http://web nchu edu tw/pweb/users/splin/
Date: 10.11.2010
Nucleic Acids
„
„
„
DNA and RNA, can always be
found in all cells of everything
from bacteria to humans. DNA
is always found in the nucleus
of the cell. RNA can also be
found in the nucleus but also
throughout the cell.
RNA is broken down into three
subcategories: messenger RNA
(mRNA) - carries the genetic
code from the DNA to the
ribosome,, transfer RNA ((tRNA)) translates this code (called
nucleotides) in the messenger
RNA into amino acids structures,
Ribosomal RNA (rRNA) - links
the amino acid chains into
proteins.
Transcription
DNA -----------------Æ mRNA
Translation
Protein
„
„
„
Hereditary information is distributed onto both
strands of a DNA molecule. Proteins constitute an
important component of hereditary information. Æ
Gene
„ refers to those segments of one strand of DNA
that are essential for synthesis of a functional
protein or one of its major subunits
(polypeptides)
„ Those
Th
segments
t off a DNA strand
t d th
thatt encode
d a
tRNA or rRNA molecule
All segments of a gene lie on the same strand
of DNA Æ Sense strand and antisense strand
Main features of gene position and orientation along
DNA:
„ Actual gene: the sequence of a gene coded on
the strand reads from 5’ to 3’ (i.e.
complementary DNA strand
strand, two strands have
the opposite sense of direction)
„ DNA strand segments coded for proteins controls
the rate of transcription Æ Gene expression: a
gene product is made Æ Gene highly expressed:
highly transcribe and translate
DNA & RNA
„
Transcription
DNA ---------------Æ
Æ
Translation
mRNA --------------Æ
Protein
„
„
„
„
Gene is a unit of heredity in a living
organism normally resides on a stretch of
DNA that codes for a type of protein or for
an RNA chain that has a function in the
organism
Genes hold the information to build and
maintain an organism
organism'ss cells and pass
genetic traits to offspring
Changes in the sequences of nucleotides
observed in the same species do not
markedly affect the gene product –
polymorphism
p
y
p
40 % of all yeast gene have a human
http://www.mctd.eu/immunesystem.html
counterpart with interchangeable function.
Ribonucleic Acid(RNA)
RNA molecules are similar to DNA,
except: ribose sugar and base
uracil(U)
RNA molecules are chains of 4
molecular base beads: fundamental
role in protein synthesis
„
„
„
DNA
Transcription
--------Æ
Æ mRNA
Translation
Protein
Transcription phase of gene expression:
DNA sequence encodes protein is
copied (transcribed) into mRNA,
regulated to adjust protein content
Translation: process of building proteins using mRNAs as templates,
templates conducted by
tRNAs (as molecular adapters)
„Nucleotides
of RNA: 2 nucleotide-invariants subunits – the phosphate group
and ribose + a nucleotide-dependent
nucleotide dependent nitrogenous base – adenine (A),
(A) guanine
(G), uracil (U), and cytosine (C) Æ AMP, GMP, UMP, and CMP
„RNA: single strand, can bind in a complementary way to DNA, in DNA-RNA
pair,
i RNA runs iin the
th opposite
it di
direction
ti to
t DNA (A,U),
(A U) (T,A),
(T A) (C,G),
(C G) and
d (G,C)
(G C) Æ
Base-pairing rule between DNA and RNA assures the information in DNA is
accurately transcribes to RNA
Types of RNA Molecules
„
„
Messenger RNA (mRNA),
(mRNA) Transfer RNA (tRNA),
(tRNA)
and ribomosal RNA (rRNA)
mRNA:
RNA complementary
l
t
copies
i off instructions
i t ti
encoded
d d on DNA
Æ Complementary-pair rule:
„
„
DNA contains
ont in master
m te copy
op of geneti
genetic info
information,
m tion kept
permanently on life, mRNA stores the working copy of this
information for a brief period
After instructions are implemented by cell, mRNA is
g
into its constituent nucleotides,, which are then
degraded
available for use in the synthesis of other molecules
tRNA
„
„
„
„
tRNAs: as a structural adapter that matches each 3-nucleotide
3 nucleotide amino
acid codon sequence of the mRNA, with the amino acid specified by this
codon
A tRNA molecule:
l
l has
h 75~
75 80 nucleotides
l tid Æ 3’ end
d off a tRNA attaches
tt h
to the specified amino acid, in the middle of tRNA are 3 bases
((anticodon)) that constitute the p
point of contact with mRNA Æ tRNA
binds to its amino acid in the cytoplasm and attaches it to the growing
chain of amino acids (polypeptide) Æ Binding site interacts with mRNA
through complementary
complementary-base
base pairing
tRNA genes are directly encoded by DNA.
3D shapes
p of tRNA molecules not onlyy bind amino acids and mRNA,, but
also interact with ribosomes
rRNA
„
„
rRNA molecules: also encoded by DNA, bind to
specific proteins and form ribosomes, contain
thousands of nucleotides
Several different types of rRNA are needed in
the synthesis of ribosomes
rRNA molecule interacts with
protein subunits (helical
cylinders, flat arrows, and
connecting wire-like regions) in
forming the ribosome in E. Coli.
RNA
„
„
„
„
„
When proteins are manufactured, the gene is first copied
into RNA as an intermediate product
Enzymatic activity: RNAs known as ribozymes are capable of
enzymatic function Æ RNA emerged before proteins and
DNA in
i evolution
l ti
Some viruses store their entire genomes in the form of RNA,
and
d contain
t i no DNA att allll Æ Synthesize
S th i their
th i proteins
t i as
soon as they are infected and without the delay in waiting
for transcription
transcription.
Proteins with incredibly diverse shapes and physicochemical
properties eventually replaced RNA as enzymes.
enzymes
DNA to form double helices have made it more stable and
attractive molecule than RNA for storing hereditary
information.
20 Amino Acids