Download 3.1 Review PBS

3.2 REVIEW PBS
What is the DNA code? What is the
connection between genes and proteins?
 DNA is read in segments, called genes
 A gene is a particular sequence of nucleotide bases
that code for a protein.
 The sequence of bases determines what sequence
the amino acids are in, which determines the
protein
How are proteins produced in a cell? How
does the sequence of nucleotides in DNA
determine the sequence of amino acids in a
protein?
 Step 1: Transcription
 DNA is too large and fragile to leave the nucleus.
 So it is copied into a mRNA template by RNA
polymerase
 mRNA acts a “messenger”, which takes the gene code
out of the nucleus to the ribosome
How are proteins produced in a cell? How does the
sequence of nucleotides in DNA determine the
sequence of amino acids in a protein?
 Step 2: Translation
 mRNA binds to a ribosome
 Ribosome reads the mRNA in three bases at a time (called
codons) These determine which amino acid is brought
 tRNA come and bind to the codons using anticodons
 This tRNA brings a specific amino acid
 This process repeats until the whole protein is made
 Therefore the sequence of DNA determines the
codons in mRNA, which determines the
sequence of amino acids, which determines the
protein being made.
How are proteins produced in a cell? How does the
sequence of nucleotides in DNA determine the
sequence of amino acids in a protein?
What determines the shape of a protein?
 Many amino acids have different properties
(positive, negative, or neutral charge). Therefore
the amino acids present and their order in the chain
affect the shape of the protein due to the following
forces:
 Van der Waals forces – random attractive forces between
atoms
 Electrostatic charge – positive amino acids will attract
negative amino acids and repel positive amino acids
 S-S – Covalent bonds between amino acids with sulfur,
these are stronger forces that hold the protein shape
steady
 Hydrogen bonds – bond formed between two molecules
that are polar… (continues on next slide)
What determines the shape of a protein?
 Polar amino acids are said to be hydrophilic
 Hydrophilic amino acids like water because they are polar like water
and will attract water.
 Nonpolar amino acids are said to be hydrophobic
 Hydrophobic amino acids are “afraid” of water because they are not
polar and will repel water (fats are hydrophobic, which is why they do
not mix with water)
 Hydrophilic amino acids will attract each other and form
hydrogen bonds. They will repel hydrophobic amino acids.
Is the shape of a protein affected by
its surrounding environment?
 In water hydrophilic amino acids will spread out
(attracted to water) and hydrophobic amino acids
will clump up (repelled by water)
 In oil hydrophilic amino acids will clump up (repelled
by hydrophobic oil) and hydrophobic amino acids
will spread out.
What is a mutation? How does a change in the
DNA code affect the shape of a protein?
• A mutation is change in one base (point mutation) or bases
(frameshift mutation due to addition or deletion of base) of DNA.
• This can change the codon, which then can change the amino
acid(s).
• If an amino acid of one property is replaced with an amino acid of
another property this can change in the interactions of the amino
acids and the shape of the protein.
Can changing just one nucleotide in a
gene change the shape of a protein?
 Yes, examples: Tay Sachs and Sickle Cell
 A single base changes glutamic acid (hydrophilic amino acid)
to change to valine (hydrophobic amino acid)
 This change causes valine (a hydrophobic amino acid) to to
stick to the hydrophobic pocket of another hemoglobin.
 The hemoglobin sticking together causes the cell to be sickle
shaped.
Key points to understand
from your portfolio:
 Page 1: Describe the 4 different types of
proteins
 Pages 2, 3, & 5: Be able to describe what
happens with transcription & translation
(using terms from pg. 5), and be able to walk
through those processes. Also, describe what
happens with protein synthesis with
individuals with sickle cell anemia (what kind
of mutation, and how does this work?)
Key points to understand
from your portfolio:
 Page 4: Compare/contrast sickle cell & Tay
Sacs. Describe the 4 forces discussed on this
page. Compare glutamic acid and valine.
Include specifics like hydrophobic or
hydrophilic, charge, and how they behave in
water. This information should help you
understand the difference in the shape of
normal RBCs compared to sickle cells.
 Page 6: Do you understand this concept map?