DNA Replication _ Protein Synthesis

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					DNA Replication
Protein Synthesis
DNA Replication
• When cells divide, they need the
  instructions on how to be a particular
  type of cell and how to function as that
  cell type.
• 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
  DNA molecules.
• 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-
  pair rule.
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
   or lunch.
 • Your DNA may have once been used in a
   dinosaur or bacterial cell – it all
DNA Replication
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?
Why 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
  the cell.
• “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
  made protein.
• 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
  same time.
• 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…

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