Download Molecular Genetics - Ursuline High School

Translation
• Once the DNA code has been Transcribed
onto a mRNA molecule, mRNA leaves the
nucleus and moves into the cytoplasm. In
the cytoplasm the mRNA combines with
the Ribosomes to make Enzymes/Proteins.
The Process of reading the mRNA code
and building a(n) Enzyme/Protein is called
Translation, or Protein Synthesis.
In order for Translation/Protein
Synthesis to occur a cell needs:
• 1. mRNA (carrying the DNA code)
• 2. Ribosomes
• 3. Amino Acids
• 4. tRNA (picks up amino acids in the cytosol
and carries them to the ribosomes where they
will be joined together to form a Protein)
The mRNA is made in the
Nucleus through the process
of Transcription. mRNA is
made up of RNA nucleotides.
Each group of 3 nucleotides is
called a Codon and codes for
one amino acid of the newly
forming Protein.
This Segment of a mRNA molecule is 7 codons long, 21
nucleotides, and will code for 7 amino acids
Ribosomes
(the ribosomes are the actual site of Translation /protein synthesis)
Made in the Nucleolus, made up of
Ribosomal RNA, rRNA
Animals and Plants get their amino acids the
same way they get their Nucleotides.
Transfer RNA (tRNA)
• tRNA is a small, folded RNA
chain (74-93 nucleotides) that
picks up and transfers specific
amino acids to a growing
polypeptide chain at the
ribosomal site of protein
synthesis during translation.
•
It has sites for Amino Acid
attachment and an Anticodon.
•
• The Anticodon is composed of
• complementary bases.
•
Each tRNA molecule binds to
only one type of amino acid.
• More than one tRNA exists for
each amino acid.
Summary of Translation
(or… so you want to make a Protein)
Let’s begin in the nucleus…… The DNA has the code to instruct the
Ribosomes as to which Proteins to make. Ok, 2 problems here: 1.) the DNA
is in the Nucleus and the ribosomes are in the Cytoplasm, and 2.) the
ribosomes can’t read the DNA. Well there’s an easy way to fix both
problems… it’s called Transcription…. Through Transcription, the DNA
code is placed onto a mRNA molecule which can 1.) leave the nucleus,
travel into the cytoplasm and join with the ribosomes, and 2.) the ribosomes
can Translate (read) the mRNA.
So now we have the DNA code, by way of mRNA, in the cytoplasm that can
instruct the Ribosomes as to which protein to make….. By the way, the
difference between one protein and another protein is the order of the
amino acids, the number of amino acids and its 3 dimensional shape.
Now …… let’s say you are a ribosome….. you are just sitting around, in
the cytoplasm, waiting for some amino acids to assemble into
protein….you already have the instructions, remember the mRNA,
…… but you can’t get the amino acids yourself…… you need help….
you need tRNA. The tRNA can pick up specified amino acids.… and
bring them to you in the correct order…..but how does I know which
amino acid to pick up?
The tRNA knows where to place its amino acid because the tRNA can
read the mRNA codon......the mRNA codon is a transcribed version of
the DNA code……it instructs the mRNA as to where it should place
the amino acid. By the way….the first amino acid is always
methionine, or sometimes referred to as “f-met”.
So…. It’s this simple….. you’re a tRNA molecule…. You have an amino
acid attached to you…… you simply move up or down the mRNA
looking for the right place to drop off your amino acid…. you’ll easily
recognize where to place the amino acid …..it’s where your anticodon
matches the mRNA codon. This process will continue until a
“termination or stop” codon, located on the mRNA, instructs the
ribosomes to break apart…..ending translation.
1st letter – Row
2nd Letter – Column
3rd Letter - Sentence
Translation
Gene Regulation
Some genes can be “switched on” or “switched off”.
When a gene is switched on….a protein is produced….
when a gene is switched off a protein is no longer
produced…. How the organism is affected depends on
the protein.
An Operon is a gene switch…. it is located on the DNA ….
What an operon really is is a series of genes that code for a
particular protein.
The first operon discovered is known as the “lac-operon”.
The lac-Operon
Four regions of DNA control the
production of a protein such as the
enzyme Beta-galactosidease (which
is used to digest lactose)
The lac-Operon
1. a structural gene that codes for the
enzyme Beta-galactosidease.
2. an operator region right in front of the
structural gene, where the repessor
molecule attaches to prevent
Transcription.
3. a promoter region where the RNA
Polymerase binds to the DNA.
4. a regulator gene which codes for the
Repressor.
5. A repressor is a molecule which binds
to the operator and prevents
transcription.
The combined region of the operator and
structural gene is called an operon.
DNA
regulator
gene
Lac-operon
Editing DNA
• About 65% of an organism’s DNA is not used…. it’s left over
baggage from evolution.
• As a consequence, about 65% of the mRNA transcribed is
also useless….. So the mRNA must be “edited” to remove
the useless codes.
• This editing is accomplished by enzymes.
• The pieces of mRNA which are spliced out are called
Introns…. of course they cannot code for anything.
• The pieces of mRNA which are left in, after editing, are
called Exons…. of course they are the expressed codes.
Examples of Genes containing Exons and Introns
The Structure
of a
Chromosome
Chromosome Maps
• A
diagram
that
shows
the
location
(locus,
plural loci) of a
gene.
MUTATIONS
The replication of DNA is usually extremely accurate
because DNA polymerase proofreads the DNA as it is
produced.
If necessary, DNA polymerase removes the incorrect
nucleotide and replaces it.
If the DNA is NOT repaired a Mutation will occur. A
mutation is a change in the DNA….. This change will
affect the protein which is produced and can eventually
affect the organism's traits.
The 2 most common causes of
mutations are:
1. Radiation (such as ultraviolet and x-ray) and,
2. Various reactive chemicals called Carcinogens.
If the Mutation occurs in a Somatic cell or body
cell, it is not inheritable.
If the Mutation occurs in a gamete, it is heritable.
Types of Mutations
(Changes in the DNA affecting the resulting traits)
The 2 most common mutations are:
1. Point Mutations
2. Frame-shift Mutations
Point Mutation
• Changes in one nucleotide in the genetic code.
• Effects - none to fatal.
• Example: Sickle Cell Anemia
Sickle Cell Anemia
Frame Shift
Imagine a sentence should read:
“the red cat ate the rat”
If a deletion occurs, a letter is removed, in this
case the first letter “e”
… the sentence would read:
“thr edc ata tat her at”
The addition of a letter, in this case the letter “o”
would result with a frame shift which looks like
this…
“tho ere dca tat ath era t”
Insertions & Deletions
• The addition or loss of a base in the DNA
Which causes a frame shift mutation.
Biotechnologies
• Cloning
• The Human Genome Project
• Gene Splicing ...What are “Restriction
Enzymes” and what are they used for?
• Gene Therapy