• When cells divide, they need the
instructions on how to be a particular
type of cell and how to function as that
• These instructions are found in the DNA
of the parent cell. It has its own full set
of DNA instructions.
• When the cell divides to form two cells –
it must make sure the new cell has a
full set of DNA as well. If one cell is to
become two cells then one set of DNA
must become two sets – this is
replication – it’s a part of mitosis.
• Semi = half
• Conserve = to keep
• Therefore…semiconservative literally
means “half is kept”.
• This means that we will use the old
DNA as a template to make two new
• Each new DNA molecule is therefore
made up of one strand from the old DNA
and a newly synthesized strand of DNA
that match up according to the base-
Replication – The Process
• Replication is a two-phase job…
1.Separate the old strands.
2.Build the new (complementary) strands.
• To perform these jobs we will use a
number of enzymes and free-floating
DNA nucleotides that we would have
gotten into the cell when we ate the
cells of another organism for breakfast
• Your DNA may have once been used in a
dinosaur or bacterial cell – it all
DNA RNA Pn
• DNA RNA Pn is known as the central
dogma of modern biology. The process it
illustrates is protein synthesis.
• Proteins build, operate and regulate the body
– pretty important stuff! In fact, the word
protein means “of primary importance”!
• DNA (deoxyribonucleic acid) resides in the
nucleus of your cells and it carries all of the
instructions on how to build your proteins.
This is why it is called the “blueprint of life”.
• DNA is the blueprint and proteins are the structures made
using the blueprint.
• So what is the role of the RNA?
• RNA (Ribonucleic acid) is the link between
DNA and proteins.
• DNA lives in the nucleus – it’s the boss that
works in the head office of the cell – it never
leaves that office!
• Proteins are built by little organelles called
ribosomes which live in the cytoplasm of the
cell – not the nucleus.
• RNA is what helps connect the DNA in the
nucleus to the ribosomes in the cytoplasm.
• Think of RNA as the messenger. It carries the
instructions from the DNA, in the nucleus, out
to the protein-building ribosomes, in the
• DNA RNA Pn (It makes more sense now eh?)
Transcription (DNA RNA)
• The first step in protein synthesis is
transcription. It takes place in the nucleus of
• “Transcript” = copy.
• The DNA is going to unwind and make a copy
of one small section of itself. This small
section is a gene – one trait about you.
• This small copy of the DNA is called mRNA
(messeneger RNA). It carries the code for one
gene on the DNA out to the cytoplasm.
• Transcription is complete once the mRNA
has been constructed.
• The mRNA will travel through one of the
pores in the nucleus out to the cytoplasm in
search of a ribosome.
Translation (RNA Pn)
• Translation is the second step of
protein synthesis. It occurs in the
cytoplasm when the mRNA is used by
the ribosome to build the protein.
• A translator is someone who takes one
language and changes it into another
language. The name translation applies
here because the ribosome is using a
nucleic acid sequence to build a protein
sequence. It is changing the sequence
of one type of biomolecule into a
sequence of another.
Translation (RNA Pn)
• Translation begins when the ribosome (the
protein builder) finds the mRNA and sits on
one end of the mRNA strand.
• The ribosome then begins moving along
the mRNA, reading the nucleotide
sequence (A’s, C’s, G’s & U’s).
• It uses this sequence to help it gather the
proper amino acids (protein building
blocks) and put them in order in the newly
• Once the ribosome reaches the end of the
mRNA – it jumps off and releases the
newly made protein. The protein can now
go and do some work in the cell.
• The ribosome (green blob) is traveling down
the mRNA strand (blue line) and reading it.
• The code on the mRNA strand tells the
ribosome which amino acids (yellow ovals)
are needed to build the protein (all the yellow
ovals connected together).
• A polysome occurs when a number of ribosomes
are translating the same piece of mRNA at the
• This gives you many copies of the desired
protein using only one mRNA. This saves the
cell energy and resources.
That’s All I Got…