Transcript I. DNA A. WHAT IS IT?

Chap. 12
DNA & RNA
I.
DNA - What is it?
• It’s the molecule that
makes- up the genetic
code.
• Polymer of double-stranded
nucleotides
Chromosome structure: (P. 297)
• DNA + histones =
chromatin
• histones + chromatin =
nucleosome
• nucleosome allow lots of DNA
to fit into a tiny space!!
• Like a tape measure!
Made of:
• 1) deoxyribose sugar
• 2) phosphate group
• 3) Nitrogen base – which are
– A)purines
• Adenine & Guanine &
– B)pyrimidines
• Cytosine & Thymine
The bases bond in a special
arrangement.
• A bonds with T
• G bonds with C
• These bonds are called
complimentary bases.
(At The Girl’s Club!!)
Major functions of DNA:
• Replication – “makin’ copies”
&
• Protein Synthesis – “tellin’
the cell what to do!”
II. A. Replication
• Process to make a copy of
the DNA.
Both strands of DNA act as
a pattern for the new
DNA strands.
B. Steps: (inside the nucleus)
• 1. Bonds between bases
weakened & strands
“unzip”.
• 2. The exposed bases bond
with their complimentary
bases found “floating”
in the nucleus.
• 3. Sugar-phosphate bonds
link.
• This links the nucleotides
together.
III. A. How does this info
(inside the nucleus)
get outside to “boss” the
cell around?”
• By using….mRNA –
messenger RNA
• It takes the message
outside to the ribosomes.
B. What is RNA?
• Ribonucleic Acid
• There are 3 types of RNA.
• It controls the synthesis
of proteins.
• Polymer of single-stranded
nucleotides
C. Made of:
1) ribose (5 - C sugar)
2) the nitrogen base Uracil
(replaces Thymine)
3) phosphate group
D. Transcription – “Cross
writing”
• uses mRNA to write a
message so the ribosomes
understand “what to do”
E. STEPS IN MAKING
mRNA:
1) Enzymes separate DNA
strands
2) Complimentary bases
attach to exposed ends.
“Uracil replaces Thymine”
• 3) Enzymes bond sugarphosphates molecules
• 4) Bonding continues until
the end.
• 5) mRNA leaves the nucleus
thru nuclear pores and
enters cytoplasm.
• Nucleotides are “read” as a
set of three called a
codon.
• Codons “carry” specific
amino acids.
• Certain codons mean start
& others mean stop.
For example…
mRNA is UCGCACGGU
codons are UCG – CAC – GGU
P. 303 Fig. 12-17 – be able to
identify the amino acids
Amino acids are
Serine – Histidine - Glycine
• QUICK LAB - P. 303
• RIGHT MARGIN
• WRITE ANSWER IN ON A
SEPARATE PAGE!
• ANSWER #1 THRU #4
• A & C #1 ONLY
IV. Translation –
Interpreting the message
to make proteins
• Uses tRNA that float
around in the cytoplasm.
A. Made of:
• An anticodon on one end 3 nitrogen bases that
bond to the codon,
• And its specific amino acid
on the other end.
B. Steps in translation:
• 1) mRNA connects to a
ribosome at the start codon
(AUG)
• 2) ribosome “reads” the
codon & identifies the
anticodon.
•(EX. codon AUG is with
anticodon UAC)
• 3) rRNA (inside the
ribosome) bonds the
tRNA to its mRNA
• 4) tRNA attaches its amino
acid synthesizing specific
proteins.
• 5) Peptide bonds unite the
amino acids.
• 6) This process continues
until it reaches a stop
codon
• The order of amino acids is
very specific for
proteins.
• Enzymes, specific
biomolecules…
SO…
• DNA has the “message” that is
replicated for all new cells.
• The message is sent out into
the cells by transcription.
• Proteins are assembled by
translating the message.
V. Mutations….
• … are “errors” in the
messages
• They could be harmful/lethal/
no affect
• Point mutations occur at one
point in the DNA sequence.
(P. 307)
• Could be substitution,
insertion or deletion of a
nucleotide.
• This is a frameshift mutation
Chromosome mutations
affect the entire
chromosome
• Could be deletion,
inversion, duplication, or
translocation
More mutations:
• Somatic cells mutations may
affect only the individual
• Sex cell mutations may
affect offspring/children
• Figure Questions – P. 307
• 1. Describe what happened
in the 1st box.
• 2. What is the effect on
the amino acid sequence?
• 3. What happened in box 2?
• 4. And the effect on the
amino acid sequence?
P. 308 Fig. 12-20
5. What happened in:
1. Deletion…
2. Duplication…
3. Inversion…
4. Translocation…