Ch' 10: How Proteins Are Made

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Ch. 10 How Proteins Are Made

• Bio P
• Mr. Q

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Section 10.1 From Genes to Proteins

• How is the information taken from DNA?
• Proteins are not directly built from DNA.
• Ribonucleic acid (RNA) is used to carry the
  information.
• It is a nucleic acid like DNA, and made of
  nucleotides.

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How do DNA and RNA differ?

• RNA is a single strand, while DNA is a double
  strand.
• RNA has the sugar ribose, while DNA has the sugar
  deoxyribose.
• RNA has the base uracil, while DNA has the base
  thymine. Like thymine, uracil pairs up with
  adenine.

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What is transcription?

• The process of transferring the information on a
  DNA onto mRNA.
• Lets remember a gene is a segment of DNA that
  codes for a protein.
• A GENE IS THE INSTRUCTIONS ON HOW TO MAKE ONE
  PROTEIN.

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What is translation?

• The process of transferring the information on a
  mRNA into a protein.
• Lets remember Where are proteins made in a
  cell? RIBOSOMES.
• mRNA TAKES THE INFORMATION TO THE RIBOSOME WHERE
  THE PROTEIN IS MADE.

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• The entire process by which proteins are made
  based on the information encoded in DNA is known
  as gene expression. See fig 10-1

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What happens during transcription?

• The information in a gene is transferred to a
  molecule of RNA.
• RNA polymerase, an enzyme that adds and links
  complementary RNA nucleotides during
  transcription.

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What are the steps of transcription? See figure
10-2

• RNA polymerase binds to the genes promoter a
  start signal.
• DNA helicase causes the two DNA strands to unwind
  and separate.
• Complementary RNA nucleotides are added.
• Transcription proceeds until it reaches a stop
  signal on the DNA

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How is the mRNA molecule put together?

• Only ONE SIDE OF THE DNA double helix is used as
  a template or pattern for mRNA.
• As the RNA polymerase adds nucleotides and they
  are joined by covalent bonds.
• See figure 10-3 in book.

http//student.ccbc.cc.md.us/biotutorials/protsyn/
transc.html
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Where does transcription occur?

• In prokaryotes (bacteria)
• In the cytoplasm, they have no nucleus.
• In eukaryotes (animal and plant cells)
• In the nucleus where the DNA is.

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What exactly is mRNA?

• messenger RNA (mRNA) carries the instructions for
  a specific protein that the cell needs and takes
  it to the site of translation.
• Once the mRNA is made it goes from the nucleus ?
  cytoplasm.
• Once in the cytoplasm it goes to the ribosomes,
  where proteins are made.

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What do the instructions look like?

• The instructions are written as a set of 3
  nucleotides sequences found on mRNA called
  codons.
• Each codon on a strand of mRNA codes for an amino
  acid, stop or start codon.
• 1 codon 1 amino acid

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• Once at the ribosome the information is
  translated from
• mRNA codons ? tRNA anticodons
• tRNA anticodons ?amino acid
• amino acids ? protein chain

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What is the genetic code and what is it used for?

• It is a chart that contains a list of the codons
  and what amino acid, start or stop codon it codes
  for.
• There are 64 possible codons.

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Where and how does translation occur?

• Translation unlike transcription takes place in
  the cytoplasm.
• With the help of transfer RNA (tRNA) amino acids
  are brought to the ribosomes.
• Each tRNA molecules has an anticodon that is
  complementary to an mRNA codon.

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Anticodon
mRNA Codon
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What is the other type of RNA?

• Ribosomes are also made partially of RNA.
• Ribosomal RNA (rRNA) is a molecule of RNA that is
  part of the ribosome.

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What are the steps of translation?

• You are basically responsible for knowing them
  from the book.
• We will have an exercise to reinforce the steps.

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Section 10.2 Gene Regulation and Structure

• How do prokaryotic and eukaryotic cells control
  which genes are expressed?
• Believe it or not there is an on-off switch.
• The operator overlaps the promoter site and is
  the switch that can be turned on and off.

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How exactly does the operator work?

• As the name implies it controls RNAs polymerase
  from attaching to the gene.
• A repressor is a protein that binds to an
  operator and physically blocks RNA polymerase
  from binding to the promoter.

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What is an operon?

• When bacteria has a set of genes that have the
  same function, the promoter site and the operator
  that controls them is known as the operon.
• Basically, in bacteria
• promoter site operator operon

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An Example The lac operon
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What is the lac operon?

• Lactose is a sugar that needs to be broken down
  by an enzyme.
• Lactose present need to metabolize (break it
  down)
• Lactose not present dont need to metabolize.

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• Not enough lactose repressor attaches,
  transcription does not occur.

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• Lactose present attached to repressor and makes
  it fall off, transcription occurs.

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How about eukaryotes?

• Gene regulation occurs before, during, and after
  transcription.
• But most occur before.
• Regulatory proteins in eukaryotes are called
  transcription factors.

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How does the DNA control gene regulation?

• DNA contains introns and exons.
• Introns are long segments of DNA (nucleotides)
  that have no coding information.
• Exons are the portions of a gene that are
  translated into proteins.

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What type of mutations can occur during
transcription?

• Point mutations occur when one or just a few
  nucleotides are changed in a gene on a chromosome.

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What are types of point mutations? See figure 10-8

• Substitution
• One nucleotide is substituted for another.
• Insertion
• One or more nucleotides are added to the sequence.

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• Deletion
• One or more nucleotides are deleted in the
  sequence.