1. RNA carries DNA’s instructions.
• The central
dogma states
that information
flows in one
direction from
DNA to RNA to
proteins.
2.RNA differs from DNA in three major ways.
– RNA has a ribose sugar.
– RNA has uracil instead of thymine.
– RNA is a single-stranded structure.
3. Protein synthesis is the cellular process in which the
DNA code is read, copied and then the instructions
are used at the ribosomes to synthesize (make)
the correct proteins.
4. Protein synthesis has 2 parts:
Transcription and translation.
5. Transcription is catalyzed by RNA
polymerase.
a. RNA polymerase and other proteins form
a transcription complex.
b. The transcription complex recognizes the
start of a gene and unwinds a segment of
it.start site
transcription complex
nucleotides
c. Nucleotides pair with one strand of the DNA.
d. RNA polymerase bonds the nucleotides
together.
e. The DNA helix winds again as the gene is
transcribed.
DNA
RNA polymerase
moves along the DNA
f. The RNA strand detaches from the DNA once
the gene is transcribed. This is called messenger
RNA (m-RNA) because it carries the DNA’s
“message” to the ribosome.
RNA
6. Transcription can actually make three
different types of RNA.
– Messenger RNA (mRNA) carries the message
that will be translated to form a protein.
– Ribosomal RNA (rRNA) forms part of ribosomes
where proteins are made.
– Transfer RNA (tRNA) brings amino acids from
the cytoplasm to a ribosome.
7. Transcription and replication are
similar. They both involve complex
enzymes and complementary base
pairing.
• The two processes have different end
results.
– Replication copies
all the DNA;
transcription copies
a gene.
– Replication makes
one copy;
transcription can
make many copies.
one
gene
growing RNA strands
DNA
Introns (junk DNA)
are also removed in
transcription
process.
1. Amino acids are coded by mRNA base sequences.
2. Translation converts mRNA messages into
polypeptides (proteins).
3. A codon is a sequence of three nucleotides
that codes for an amino acid.
codon for
methionine (Met)
codon for
leucine (Leu)
EACH CODON CODES FOR 1 AMINO
ACID. THERE ARE 20 AMINO ACIDS,
THEREFORE THERE ARE MULTIPLE
CODES FOR EACH AMINO ACID.
There are a total of 64 possible codes.
4.The genetic code matches each codon to its amino
acid or function.
– one start
codon,
codes for
methionine
– three stop
codons
The genetic code matches each RNA codon with its amino acid or function.
5. A change in the order in which codons are
read changes the resulting protein.
6. Regardless of the organism, codons code
for the same amino acid.
7. Amino acids are linked to become a protein.
8. An anticodon is a set of three nucleotides
that is complementary to an mRNA codon.
An anticodon is carried by a transfer RNA
(tRNA).
When the t-RNA is
carrying its amino
acid it is said to be
“charged”.
9. Ribosomes consist of two subunits.
– The large subunit has three binding sites for
tRNA.
– The small subunit binds to mRNA.
10. For translation to begin, tRNA binds to a start
codon and signals the ribosome to assemble.
11. A complementary tRNA molecule binds to
the exposed m-RNA codon, bringing its amino
acid close to the first amino acid.
12. The ribosome helps form a polypeptide bond
between the amino acids.
13. The ribosome pulls the mRNA strand the
length of one codon.
14. The now empty tRNA molecule exits the
ribosome.
15. A complementary tRNA molecule binds to
the next exposed m-RNA codon.
16. Once the stop codon is reached, the
ribosome releases the protein and the
ribosome disassembles.
17. Now the new protein has been synthesized
following the precise code from the DNA.
ANIMATION #1
http://www.ncc.gmu.edu/dna/ANIMPROT.htm
ANIMATION WEBSITE #2
http://omega.dawsoncollege.qc.ca/ray/protein/panim.htm
ANIMATION WEBSITE
http://tidepool.st.usm.edu/crswr/protsynthmov.html