Transcript 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
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
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 DNARNA
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
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
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.