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Chapter 10: Nucleic Acids and Protein Synthesis

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Chapter 10: Nucleic Acids and Protein Synthesis 10-1 DNA 10-2 RNA 10-3 Protein Synthesis Extra Slides AND Answers for Critical Thinking Questions (1) Yes. – PowerPoint PPT presentation

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Title: Chapter 10: Nucleic Acids and Protein Synthesis


1
Chapter 10 Nucleic Acids and Protein Synthesis
10-1 DNA
10-2 RNA
10-3 Protein Synthesis
2
10-1 DNA
I. Structure of DNA (stores INFORMATION for
PROTEIN making)
  • DOUBLE-stranded nucleic acid ? backbone and
    nucleotide SEQUENCE.

3
(1) Deoxyribose (The Backbone)
  • 5-C sugar of DNA that LINKS a PHOSPHATE with a
    NITROGENOUS BASE.

4
(2) Nitrogenous Bases (The Instructions)
  • 4 TYPES of RUNGS of a DNA ? 1 part of a
    NUCLEOTIDE (Adenine, Thymine, Cytosine, Guanine
    ARE the bases)

5
(3) Purines (i.e., Adenine and Guanine)
  • N-bases with TWO rings of C and N atoms (bond to
    a PYRIMIDINE).

6
(4) Pyrimidines (i.e., Cytosine and Thymine)
  • N-bases with ONE ring of C and N atoms (bonds to
    a PURINE).

7
(A) The Double Helix (1953, James Watson and
Francis Crick)
  • Two backbones bonded by rungs (HYDROGEN Bonds)
    ? a double SPIRAL (i.e., COVALENT bonds holding
    sugar-phosphate backbone together).

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(B) Complementary Base Pairing (who bonds to who?)
  • Base-pairing RULES of DNA ? TWO base pairs form
    due to WEAK HYDROGEN bonding between bases

Adenine-Thymine (A-T) 2 H-bonds
Cytosine-Guanine (C-G) 3 H-bonds
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II. Replication of DNA (during S phase of cell
cycle)
  • TWO nucleotide strands UNZIP and UNWIND ? EACH
    strand serves as a TEMPLATE for a new COPY.

12
(1) Replication Fork (marks a LOCATION for
replication to begin)
  • POINT where TWO chains are SEPARATED by enzymes
    (HELICASES).

13
Critical Thinking
(1) A DNA molecule (labeled as A) replicates to
produce two new DNA molecules (labeled as B).
Both of the B DNA molecules then replicate to
form four new DNA molecules (labeled as C). Are
any nucleotide chains from A present in the C DNA
molecules? Explain your answer. If you believe
the answer is yes, how many of the A DNA
nucleotide chains are present in the C DNA
molecules?
14
(2) Helicases (nuclear enzymes used for
replication AND transcription)
  • Enzymes move along DNA, breaking H-bonds between
    base pairs, causing two DNA sides to SEPARATE.

15
(3) DNA Polymerase (nuclear enzyme used for
BUILDING DNA)
  • Enzyme BUILDS TWO new IDENTICAL strands from
    UNZIPPED DNA, using complementary BASE PAIRING.

16
(A) Accuracy and Repair (of DNA during
Replication)
  • During replication, about ONE error occurs in
    every 10,000 paired nucleotides (due to
    proof-reading enzymes).

17
(1) Mutation (caused by mutagens OR proofreading
errors)
  • A change in the ORIGINAL nucleotide (BASE)
    sequence due to a MISTAKE in replication.

NOTE The combination of DNA proofreading and
repair processes help keep the ERROR RATE one per
1 BILLION nucleotides.
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10-2 RNA
I. Structure of RNA (Ribonucleic Acid)
  • RNA is SINGLE-stranded, w/ Ribose, Uracil, and
    exists in 3 TYPES.

25
(1) Ribose (replaces deoxyribose, found in DNA)
  • SUGAR of the sugar-phosphate BACKBONE in RNA.

26
(2) Uracil (NO Thymine in RNA)
  • A new BASE bonds to ADENINE (in place of Thymine
    in RNA) U-A in RNA.

27
(A) Types of RNA (mRNA, rRNA, and tRNA)
  • 3 types are needed to complete PROTEIN
    SYNTHESIS, using original DNA.

28
(1) Messenger RNA (mRNA)
  • Carries a COPY of DNAs SEQUENCE out of NUCLEUS
    to CYTOSOL (NOTE mRNA is single stranded).

29
(2) Transfer RNA (tRNA)
  • A single chain of RNA folded into a t shape
    ? transfers an AMINO ACID (45 types of tRNA found
    floating in the CYTOSOL).

30
(3) Ribosomal RNA (rRNA ? make up RIBOSOMES)
  • RNA bound to GLOBULAR proteins where PROTEINS
    are ASSEMBLED (on the protein workbenches).

31
II. Transcription (DNA ? mRNA in the NUCLEUS)
  • Only the REQUIRED sequence of DNA BASES are
    copied onto mRNA and will LEAVE the nucleus for a
    RIBOSOME.

32
(A) Steps of Transcription (what to COPY, when?)
  • GOAL BEGIN copying and END copying the desired
    DNA sequence at the CORRECT LOCATION.

33
(1) RNA Polymerase (like DNA Polymerase)
  • Enzyme (light blue) transcribes (copies) a
    specific sequence (dark blue) of DNA onto a new
    molecule (yellow) (mRNA).

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(2) Promoters (promoter (BEGIN) ? termination
signal (END))
  • RNA polymerase INITIALLY binds to PROMOTER, in
    order to mark BEGINNING of the TRANSCRIPTION.

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(3) Termination Signal (Polymerase releases DNA
and mRNA)
  • A specific SEQUENCE of bases that marks END of
    transcription.

38
Critical Thinking
(2) Does it matter which of the separated DNA
chains is used for transcription? Why or why not?
39
(B) Products of Transcription
  • A SEQUENCE of mRNA must find a ribosome to be
    TRANSLATED.

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10-3 Protein Synthesis
I. Protein Structure and Composition (proteins
are also called polypeptides)
  • POLYPEPTIDE chain of AMINO ACIDS is linked by
    PEPTIDE BONDS.

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NOTE Although only 20 types of amino acids
EXIST, a polypeptide can BE MADE OF 100s to
1,000s of AA in sequence, depending on size of
protein.
  • SEQUENCE of the AA determines 3-D SHAPE of
    protein ?Determines FUNCTION of protein. (shape
    influences ability to bind to other molecules)

49
II. The Genetic Code (RNA ? Amino Acids)
  • Translates mRNA sequences into AMINO ACID
    sequences, and ultimately PROTEINS. (1960s)
  • Note DNA and RNA are read (interpreted) in
    TRIPLETS (3 nucleotides at a time) Ex DNA may
    read AAT CCG ATC

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(1) Codon (Triplet of mRNA ? one mRNA may have
MANY codons)
  • Exists in 64 combinations AND each codes for
    amino acid (Ex AUG codon).

NOTE Most code for an AMINO ACID, however there
are TWO types of codons that do NOT code for an
amino acid AND play a different role during
protein synthesis.
52
(2) Start Codon (AUG)
  • Coding for Methionine, and SIGNALS to RIBOSOME
    to START TRANSLATING.

53
(3) Stop Codon (Ex UGA ? NO Amino Acid at this
location)
  • SIGNALS to ribosome to STOP translating mRNA and
    RELEASE the polypeptide (protein).

54
III. Translation (Step FOLLOWING Transcription)
  • Translating mRNA with tRNA into an AMINO ACID
    SEQUENCE for a specific protein.

NOTE Transcription and Replication (NUCLEUS) of
a cell, Translation MUST occur in the CYTOSOL
where the ribosomes are located.
55
Critical Thinking
(3) How is a system composed of THREE bases per
codon better suited to code for 20 amino acids
than a system composed of TWO bases per codon?
56
(A) Anticodons and tRNA (codon-mRNA triplet,
anticodon-tRNA triplet)
  • Anticodon (tRNA) in cytosol will bond to its
    proper codon (mRNA) ? Links AMINO ACIDS
    together ? PROTEIN is made.

57
(1) Anticodon (coat hanger triplet of tRNA)
  • CARRIES an amino acid and BONDS to mRNA codon
    found on the RIBOSOME.

Ex In a sequence of mRNA AGG UUA CGA, there
are 3 CODONS
Resulting 3 tRNA ANTICODONS that bond to THIS
SEQUENCE, carrying with them, 3 AMINO ACIDS would
be
tRNA UCC AAU GCU
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(B) Ribosomes (protein and rRNA ? Nucleolus)
  • Protein WORKBENCHES where proteins are
    ASSEMBLED.
  • Hold THREE binding sites that are key

(1) ONE Site for mRNA codon.
(2 and 3) TWO sites for tRNA anticodon.
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Critical Thinking
(4) What would translation of the mRNA transcript
UAACAAGGAGCAUCC produce?
62
(C) Protein Synthesis (Rough ER ? Exported, Free
Ribosome ? Used in cell)
  • Once BUILT from amino acids, a protein can be
    MODIFIED. (typically Met gets removed, the 1st
    AA)

NOTE Several ribosomes (i.e., a polysome) can
simultaneously translate same mRNA transcript
(Ex Imagine a rope overhanging 4 or 5
workbenches)
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Extra Slides AND Answers for Critical Thinking
Questions
(1) Yes. Each replicated DNA molecule is a
hybrid consisting of one new nucleotide chain and
one original nucleotide chain. Two of the eight
nucleotide chains would have originated from the
A DNA molecule.
(2) Yes. Because templates are complementary,
they do not contain identical sequences of
nucleotides. A sequence complementary to the
template will code for different information.
(3) No protein would be produced because the mRNA
begins with a stop codon, not a start codon.
(4) Three bases per codon provide more than
enough units for the 20 amino acids that make up
proteins. Two bases would provide only 42 or 16
units.
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