Unit 3: Lecture 13

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64 Terms

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How many strands are synthesized in DNA replication?
Two strands b/c of DNA's antiparallel nature (leading and lagging strand)
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What is the leading strand?
The strand that is continuously created by DNA polymerase III b/c it is following behind the replication fork (where helicase is located)
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What is the lagging strand?
\-The strand that requires constant "priming"

\-grows backward
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How does priming work in a lagging strand?
Every time DNA helicase unfolds a segment of DNA an RNA primer is placed onto the lagging strand where DNA polymerase III will add nucleotides until it runs into another primer
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What are the fragments temporarily created on the lagging strand called?
Okazaki fragments
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What is the role of DNA polymerase I?
Removes the RNA primer and replaces it with DNA
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What is the role of DNA ligase?
Seals the gap between Okazaki fragments (forms phosphodiester bonds)
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How many replication forks are there at the origin of replication?
2 replication forks
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What happens to the end of the strands if it is not long enough to synthesize (min. 5 nucleotides long)?
Telomeres are added to protect the ends
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What are telomeres?
Special nucleotide sequences at the end of eukaryotic chromosomes created by an enzyme
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What is telomerase?
Contains an RNA template to help synthesize the complementary DNA sequence. Human telomere composed of TTAGGG repeats
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What happens to telomeres with age?
Telomeres shorten (helps determine age)
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Do all adult cells continue extending their telomeres?
No, when some reach a critical length, they stop proliferating
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What might shorter telomeres do?
Protect cell from cancerous growth by limiting the number of cell divisions; cancer cells exploit this b/c elongating a telomere of a healthy cell can create cancer cells
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What is the error rate of DNA replication?
1 error per 100,000 bp ; Actual error rate: 1 error per 10,000,000,000 bp
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Why is the actual error rate of DNA replication so low?

1. Proofreading
2. Mismatch/ Nucleotide excision repair
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Define nuclease.
Enzyme that cuts out and replaces damaged stretches of DNA
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Why must sequence changes be fixed?
Sequence changes may become permanent and can be passed onto the next generation; the mutation can potentially become a tumor
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Are all changes (mutations) bad?
No, many are the source of genetic variation upon which natural selection operates
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What will happen when DNA polymerase III places a mismatched base?
It will notice the mistake and correct it or the NER (nucleotide excision repair) pathway will notice and correct it; the mistake must be fixed before division (otherwise a mutation will occur)
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What are thymine dimers?
Two thymines next to each other connected w/ a double covalent bond when exposed to UV light making it unable to bind w/ Adenine in the other strands due to lack of available electrons
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What is the most common energy currency of the cell?
ATP
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What are the energy storing molecules needed for cellular respiration?
ATP, NADPH, NADH (NAD+), FADH (FAD+), FADH2
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What does ATP do?
Supplies most of the immediate energy that drives metabolism in living things
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What does ATP do when converted to ADP?
Releases energy
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How do cells release the energy?
ATP hydrolysis: ATP + H2O -\> Pi + ADP
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What is Pi?
Inorganic phosphate (free unbound phosphate group)
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How does ATP hydrolysis release energy?
By transferring its third phosphate to some other molecule, changing its shape (phosphorylation)
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How quickly is ATP used compared to monosaccharides?
MS: 1-2 hours; ATP: immediately
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What does cellular respiration do for ATP?
Recharge it; ADP\= 50% charged; AMP\= 0% charged
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What type of organisms perform cellular respiration?
All living organisms (every living thing needs ATP)
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Define cellular respiration.
The process that releases energy (slowly) by breaking down glucose and other food molecules in the presence of oxygen; exergonic reaction
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What can be used as fuel for cellular respiration?
Carbohydrates, fats, proteins, and glucose (most common)
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Define aerobic respiration.
Occurs in presence of oxygen
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Define anaerobic respiration.
Occurs w/o presence of oxygen
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Define photosynthesis.
Converts energy from the sun into sugars that store potential energy; endergonic reaction
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What is the formula for cellular respiration?
C6H12O6 (glucose) + 6O2 (oxygen) -\> 6 CO2 (carbon dioxide) + 6H2O (water) + ATP (energy)
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What is the formula for photosynthesis?
6 CO2 (carbon dioxide) + 6H2O (water) + light energy-\> C6H12O6 (glucose) + 6O2 (oxygen)
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Where is energy stored in a molecule of glucose?
Chemical bonds
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Glucose is an \_______________.
Electron donor
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How are electrons passed from atoms/molecules in chemical rxns (especially in cellular respiration)?
Oxidation & reduction (always occur together) AKA redox rxns
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Do electrons transfer during chem rxns release energy?
Yes, energy stored in organic molecules is released and will be used to synthesize ATP
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Define oxidation.
The process of losing an electron (often a whole H atom)
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Define reduction.
The process of gaining an electron (often a whole H atom)
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LEO says GER.
Loses Electrons \= Oxidation; Gains Electron \= Reduction
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Define reducing agent.
X loses electrons; X is oxidized by Y (becomes more positive)
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Define oxidizing agent.
Y gains electrons; Y is reduced by X (becomes more negative)
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What is oxygen?
A common electron acceptor (the final e- acceptor in cellular respiration); highly electronegative
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Why is sugar a good molecule for cellular respiration?
Electrons can be easily taken by electron carriers (NAD+ and FAD
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Electron carriers are members of the \______________________.
B vitamin family
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Why is H atom taken by oxygen at the end?
Anything that is charged and free will cause a lot of damage
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What is the difference between NAD+ and NADH?
NAD can easily pick up and release electrons (a carrier). Is reduced to form NADH, which contains a lot of potential energy
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During cellular respiration, what happens to the potential energy stored by the electrons?
An electron loses potential energy when it is transferred to oxygen
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What are the four stages of cellular respiration?

1. Glycolysis
2. Pyruvate Oxidation
3. Citric Acid Cycle
4. Oxidative Phosphorylation
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What is the main form of energy produced in cellular respiration?
ATP
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What is the first stage of cellular respiration?
\-"Splitting of sugar" breaks down glucose into two molecules of pyruvate

\-occurs in the cytoplasm and has two major phases: energy investment phase (energy spent) and energy payoff phase
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What occurs in the energy investment phase?
Glucose is phosphorylated to Glucose 6-phosphate faster by the enzyme hexokinase ("kinase"- phosphorylate something); requires ATP
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What is the input and output of glycolysis per glucose?
Input: 1 Glucose, 2 NAD+, 2 ADP + 2P Output: 2 pyruvate, 2 NADH + 2H+, 2 ATP
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What are the two ways to make ATP?

1. Substrate-level phosphorylation
2. Oxidative phosphorylation; difference between the two is where the phosphate comes from
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Explain the first way to make ATP.
Substrate-level phosphorylation: an enzyme transfers a phosphate group from an organic substrate onto ADP, forming ATP
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Explain the second way to make ATP.
Oxidative phosphorylation: the generation of ATP is driven by the flow of electrons. ADP + Pi, forming ATP
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Where does pyruvate oxidation take place?
Mitochondrial matrix
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What are the inputs and outputs of pyruvate oxidation?
Inputs: 2 CoA, 2 Pyruvate, 2 NAD+ Outputs: 2 Acetyl CoA, 2 CO2 (exhaled out), 2 NADH
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Is any ATP made by pyruvate oxidation?
No