Objectives:
1. Explain the structure of RNA
2. Explain how proteins are made in the cell.
3. Explain the function of mRNA, rRNA and
tRNA
1.
2.
3.
4.
5.
In your investigation yesterday, you mixed
banana with dish detergent. What was the
purpose of this?
In this experiment how did I break apart the
cell wall?
Why is DNA considered to be the source of
diversity among all living things?
Copy this DNA sequence and write its
complementary sequence.
GAA TTA ACA
What is the purpose of DNA replication?




all the codes located on the DNA of the 23
pairs of chromosomes are referred to as the
genetic code
the genetic code consists of the lengthwise
sequence of nitrogen bases found along a
DNA molecule e.g. ATTGCAGGCCTAATT
the genetic code is written in triplets of
nitrogen bases (three letter words or codons)
e.g. ATT GCA GGC CTA ATT
each triplet represents one amino acid in the
final protein





RNA is a type of nucleic acid
It is a three part molecule including a
phosphate, sugar and nitrogen-containing
base component.
The sugar is ribose and the nitrogencontaining base is one of the following four:
adenine, cytosine, guanine or uracil
It is single stranded
It is a helper to DNA allowing protein
synthesis to occur.



in the genetic code, more than one codon can
be used to code for a particular amino acid;
e.g. serine is coded for by UCU, UCC, UCA, or
UCG
there are three “STOP” codons, which do not
code for any amino acids, but which indicate
the end of the protein chain
the genetic code for amino acids is universal
in all living organisms
◦ a gene from one species may be inserted into
another species, and be fully functional e.g.
bacteria, using a human gene to produce insulin –
a protein

1)
2)
Protein synthesis (building of a protein in the
cell) is a 2 step process:
Transcription (copying DNA in the nucleus)
Translation (building a protein in the
cytoplasm)



Transcription occurs in the nucleus
it involves DNA and mRNA
one DNA gene is “transcribed” (copied) to
form a complementary copy referred to as
messenger RNA (mRNA)




DNA unwinds or unzips at a specific gene site
remember, a gene is a short segment of DNA
coding for a single protein
one side of the DNA gene, the template
strand, will be copied
free RNA nucleotides in the nucleus form
complementary base pairs with the template
DNA strand



the new mRNA molecule formed is a single
linear strand
mRNA then leaves the nucleus and enters
the cytoplasm
mRNA attaches itself to a ribosome
NOTE:
 a sequence of 3 nitrogen bases on mRNA is
referred to as a codon.
 these codons are complementary to the
triplets of the original DNA gene
 thus, a mRNA molecule is a complementary
copy of a gene on the DNA molecule and
carries the genetic information on how to
build a particular protein



Translation occurs in the cytoplasm
it involves mRNA, the ribosome, tRNA and
amino acids
the codons on mRNA are “read” and
“translated” by the ribosome into a sequence
of amino acids that will form a protein
molecule




mRNA arrives from the nucleus and attaches itself
to a ribosome
the first mRNA codon is in the first slot on the
ribosome awaiting tRNA
a tRNA molecule in the cytoplasm picks up an
amino acid that corresponds to its anti-codon
the tRNA and its attached amino acid then travels
to the ribosome and the anticodon on tRNA
bonds with the codon on mRNA following the
complementary base pairing rule. This ensures
that the correct amino acid is in place




the second mRNA codon is available in the
second slot on the ribosome (A site)
a second tRNA with its attached amino acid
arrives and its anticodon bonds to the mRNA
codon
now the two amino acids are bonded together
forming a peptide bond, with the help of an
enzyme
the first tRNA leaves, and the ribosome shifts
down the mRNA, exposing the third codon



this process continues until all the amino acids
have been bonded together into a long chain
when the ribosome reaches a stop codon, no
more amino acids are added and the building of
a polypeptide, which is a small portion of what
will become the large protein molecule, is
complete
the protein is released and folds up into its final
functional form


http://www.youtube.com/watch?v=NJxobgkP
EAo
http://www.youtube.com/watch?v=983lhh20
rGY&feature=related
1. Compare DNA and RNA. What is the function of each?
Where is each located in a cell?
2.
3.
4.
Why is genetic material crucial to the well-being of a
cell
State the function of rRNA, mRNA and tRNA
Draw a diagram illustrating the process of protein
synthesis. Make sure to label your diagram.