Download RNA

Central Dogma
DNA  RNA  Protein
…..Which leads to
Traits
How Does DNA produce traits?
1. Genes control proteins which determine traits
2. Order of nucleotides in the DNA determines
amino acid sequence
 RNA's act as 'go-between' for DNA
 Gene- a sequence of DNA with a specific
function
RNA
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Single strand of nucleotides (unlike DNA)
Contains 5-C sugar ribose
Uracil replaces Thymine
3 types of RNA produced
1. Messenger RNA (m-RNA) - code for order of amino acids
2. Transfer RNA (t-RNA) - carry amino acids and fit them in
proper place
3. Ribosomal RNA (r-RNA) - major component of ribosome;
large and small subunits
a. P site: carries the growing polypeptide chain
b. A site: delivers the next amino acid to the growing
chain
Codons
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Codons – 3 nucleotide sequences coded from
the original DNA strand onto a mRNA strand.
Each codon corresponds to an amino acid or a
stop/start signal
The codon on a mRNA strand is
complementary to an anti-codon on tRNA
Codons in mRNA
Going from DNARNA
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1.
2.
3.
Transcription - Formation of m-RNA
molecule from a DNA template – occurs in
the nucleus.
Occurs in three steps:
Initiation
Elongation
Termination
Initiation
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RNA polymerases bind to DNA at regions
called promoters (initiation site, also called
TATA box); the enzyme then separates the 2
DNA strands and transcription begins.
RNA polymerase reads DNA from 3’ to 5’
Elongation
• RNA polymerases move along the DNA and:
-untwists and opens a short segment of DNA
(DNA template)
- links incoming RNA nucleotides to the 3' end
of the elongating strand; RNA grows one
nucleotide at a time in the 5' to 3' direction
Termination
Transcription proceeds until RNA polymerases
reaches a termination site on the DNA; RNA
molecule is then released and leaves the nucleus.
The DNA strand then joins back together –
unchanged.
Translation
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Translation – using the mRNA strand made
during Transcription and tRNA and rRNA to
build a protein.
Occurs at the site of protein synthesis – the
ribosome.
Occurs in three steps – the same but different
than transcription – initiation, elongation, and
termination.
Initiation
1. the small ribosomal subunit
attaches to the 5' end of the
mRNA ('start' codon -AUG)
2. a tRNA (with anticodon UAC)
carries the amino acid methionine
to the mRNA
Elongation
1. the next tRNA binds to the ribosome; the
new amino acid is attached to first one
2. the first tRNA is released and binds again
with other amino acids (repeated deliveries)
3. a new tRNA attaches to the ribosome and
repeats the process, thereby increasing the
polypeptide chain length
Termination
1.
2.
Occurs when the ribosome
encounters a 'stop' codon.
The resulting protein formed is
now released and is used by the
cell.