Chapter 10 – Nucleic Acids and Protein Synthesis
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Chapter 10
Nucleic Acids and
Protein synthesis
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DNA = ___________________________ – stores and transmits the genetic information that
tells cells which proteins to make and when to make them.
DNA is made up of 2 long chains of _________________________.
Nucleotide = __________________ + _____________ + ____________. See fig. 10-1 on pg. 185.
4 Nitrogen Bases = ____________, ______________, ____________, and _____________.
Purines – (have 2 carbon rings) = ________________________
Pyrimidines – (have 1 carbon ring) = ________________________.
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See fig. 10-2 on page 186.
____________________________________ – (1953) – suggested the “double Helix” model for
the structure of DNA. See fig. 10-3 on pg. 186.
____________________________________ – took x-ray pictures of DNA crystals (x-ray
crystallography). This helped confirm Watson/Crick’s idea.
1962 Nobel Prize in Medicine – went to Watson, Crick, and Wilkins. This has been called the
discovery of the century. Unfortunately, Rosalind Franklin died in 1958 and her work was not
recognized.
Chapter 10 – Nucleic Acids and Protein Synthesis
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Structural Details of DNA:
___________________________ Backbone is bonded covalently.
____________ bases face toward center of helix.
DNA is “double stranded”.
Bases on 1 strand face bases on the other strand.
Weak hydrogen bonds form between the bases, holding the 2 strands together.
Purines ALWAYS pair with pyrimidines. This keeps the pairs of bases, between the uprights of
the DNA ladder, at a uniform length.
_____________________________________ Rules :
- Adenine always bonds with Thymine.
- Cytosine always bonds with Guanine.
NOTE: The base sequence on 1 strand is an exact “complement” of the sequence on the
other strand. See fig. 10-3 on pg. 186.
QUESTION – If one strand has the following sequence: AGTCCATTGAAC, what would the
complementary sequence be on the other strand??
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In cell division, the ability of DNA to make exact copies of itself is important……Understanding
base sequences led to ideas of how DNA might copy itself.
Replication – ______________________________.
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Steps of DNA Replication:
(See fig. 10-5, pg. 188)
2 nucleotide chains separate at the “__________________”. NOTE – __________ enzymes
break hydrogen bonds between bases to “______” DNA.
_____________________ – bind to the separate chains of nucleotides (1 nucleotide at a time).
The polymerases build a new complimentary chain of nucleotides. NOTE – New strands are built
for BOTH of the unzipped DNA chains.
At the end of replication, there are 2 identical copies of the original DNA molecule. Each DNA is
made up of 1 chain from the ORIGINAL DNA and 1 NEWLY MADE chain.
Chapter 10 – Nucleic Acids and Protein Synthesis
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NOTE – DNA replication happens ___________________________________________. It does
NOT begin at 1 end and proceed to the other.
NOTE – Replication occurs in _________________ directions on the 2 strands.
DNA Replication is ____________________:
- Approximately _________________________ paired nucleotides occurs.
- DNA proofreading and repair enzymes cuts the error rate to _________________ nucleotides.
Proofreading and Repair Enzymes – Scan DNA for errors, Chemically “snip” them out and “glue”
in the correct sequences.
_______________ – a change (error) in the nucleotide sequence….may have no effect or may
have serious consequences. Caused by a variety of agents including chemicals, radiation, UV
light from sun.
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RNA
RNA = ____________________________ – SINGLE stranded. It __________________________
____________________________________________ in the cytosol.
RNA is similar to DNA but:
- It is __________________________.
- The sugar is ____________ instead of _____________________.
- _____________ replaces ______________.
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3 Types of RNA:
(Each has a different job)
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______________________________ – (mRNA) – nucleotides are in a single uncoiled chain. It
carries genetic information from the DNA in the nucleus to the cytosol.
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_____________________________ - (tRNA) – single chain folded into a cloverleaf shape. Binds
to specific amino acids. See fig. 10-8 on pg. 194.
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_____________________________ – (rRNA) – most abundant form. Its structure is “globular”.
It makes up the ribosomes where proteins are put together.
Chapter 10 – Nucleic Acids and Protein Synthesis
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TRANSCRIPTION
Transcription – process by which __________________________________________________
_______________. OCCURS IN THE NUCLEUS. Read pages 191 – 192. Continued on next slide…
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Steps of Transcription:
______________________ = transcription enzyme – _________________________________
_______________________ ( these regions have lots of A-T base pairs) on the DNA.
Promoter Region – _____________________________________________________
RNA polymerase attaches to 1 strand of unzipped DNA and begins pasting together
complementary RNA nucleotides to form a strip of RNA. NOTE – Base pairing rules are the same
as in DNA replication, EXCEPT URACIL REPLACES THYMINE!!
Transcription continues until the RNA polymerase ____________________________________
_______________________________________ = specific sequence of nucleotides that marks
the end of a gene or genes.
NOTE – All 3 types of RNA (mRNA, tRNA, and rRNA) are transcribed this way.
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Protein Synthesis
Protein Synthesis = _______________________. NOTE – all 3 types of RNA will be at work here.
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Protein Structure & Composition: Key Points
Proteins are polymers made up _______________________________ (chains of amino acids –
“aa” from here on out).
There are ______ different aa’s that make up proteins.
Proteins may consist of 100’s or 1,000’s of the 20 different aa’s arranged in a particular
sequence.
The aa sequence determine how a polypeptide will bend and twist to form the 3-D structure of a
protein.
The 3-D ___________________________.
Chapter 10 – Nucleic Acids and Protein Synthesis
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Genetic Code – the link between the nucleotide sequence in DNA and the aa sequence in
proteins.
Codon – _____________________________________. Each codon codes for a ___________.
See table 10-1 on pg. 194.
Facts About the Genetic Code:
- several codons code for each aa.
- Start Codon = ________ – engages a ribosome to start translation (also codes for the aa –
Methionine).
-Stop Codon - = ______, ______, ______ – cause the ribosome to stop translating.
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Translation – ________________________________________________________. After mRNA
is made, it leaves the _______________ and migrates to a ____________ in the _____________
– THIS IS THE SITE FOR PROTEIN SYNTHESIS!!
_____ – bonds to and transports an aa to the ribosome = “aa taxi cab”. See fig. 10-8 on pg. 194.
_______________ – sequence of 3 nucleotides that is complementary to pairs with a
corresponding mRNA codon. If ACA is the codon, then UGU would be the anticodon.
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Ribosome – site for protein assembly. It can float freely in the cytosol or can be attached to the
endoplasmic reticulum (ER). It is made up of rRNA and proteins that hold it together.
- free floating ribosomes make proteins to be used WITHIN the cell.
- ribosomes attached to the ER make proteins to be exported OUT OF THE CELL.
3 binding sites on a ribosome – (Key to Translation):
- 1 site that anchors the mRNA that is going to be translated.
- 2 sites that hold the tRNA “taxi cabs”.
SEE fig. 10-9 on pg. 195.
Chapter 10 – Nucleic Acids and Protein Synthesis
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Steps of Translation =
(Protein Synthesis)
See fig. 10-9, pg. 195
1. Ribosome attaches to the ___________________ = methionine on the mRNA transcript.
Therefore, the 1st aa in every protein chain is _____________________.
2. As the ribosome move s along the mRMA, each mRNA codon is sequentially paired with its
__________________________ (aa taxi cab).
3. aa’s are hooked to a growing polypeptide chain In the order specified by mRNA.
4. As each aa is added, the ribosome moves ahead 3 nucleotides (1 codon) on the mRNA
transcript.
5. Eventually the ribosome reaches a ___________________….this ends translation.
6. mRNA is released from ribosome and polypeptide chain (protein) is complete.
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NOTE :
- Several ribosomes may simultaneously translate the same mRNA. As soon as 1 ribosome is out
of the way, another follows behind.
- Translated polypeptide chain = PRIMARY structure of a protein. As it folds and joins other
chains, it becomes the functional structure of a completed protein.
- mRNA breaks down rapidly. Its parts are recycled and used in the future.