Untitled Flashcards Set

CELLULAR RESPIRATION

• Main three phases of Cellular respiration:

1. Glycolysis - breakdown of 6-carbon glucose molecule to create two 3-carbon pyruvate molecules, reduce 2 NAD+ to 2 NADH, and 2 net ATP (from payoff phase, as 2 ATP used up in investment phase) (Substrate-level phosphorylation)

2. Krebs Cycle - Takes place in the matrix of mitochondria. First pyruvate oxidation is required before it enters the matrix, as the pyruvate is oxidized into 2 Acetyl-CoA as NAD+ is reduced to NADH during that process, a 2-carbon molecule with a Coenzyme A attached to it. It then is able to enter the cycle which 6 NADH, 2 FADH2, 4 CO2, and 2 ATP is produced for both Acetyl-CoA (Substrate-level phosphorylation)

3. Electron transport chain - uses the coenzymes, NADH and FADH2 and oxidizes them back after they reach complex I and II in which the electrons are turned into high energy electrons that power the transport pump that sends H+ across the concentration gradient. The electrons pass through the complexes and electron holders until it reaches its final acceptor of oxygen (creates H2O). The formulation of the concentration gradient (chemiosmosis) allows the H+ ions to flow through ATP synthase which proteins associated with it spin and attach ADP to a Pi. (Oxidative phosphorylation)

• CoQ and CytC are mobile electron carriers within the ETC

THEORETICAL - 36 ATP per glucose molecule

• When a reaction breaks bond, like ATP turning into ADP+Pi as is loses a phosphate, that is a exergonic process (-DeltaG)

• When a reaction adds a bond, builds a molecule like ADP+Pi to turn into ATP, it is an endergonic process because it uses that energy to create covalent bonds. (+DeltaG)

• Aerobic respiration - occurs when O2 is present within the cell (Glycolysis does not need oxygen to occur)

• Anaerobic respiration - occurs when there is no oxygen in the cell, fermentation occurs and it oxidizes NADH back to NAD+ for Glycolysis. (Only produces about two ATP)

• Aerobic respiration makes more ATP per molecule of glucose, while fermentation makes more ATP per unit of time

• Fermentation in yeast cells have ethanol as byproduct, while in muscle and some bacteria cells produces lactate as byproducts

• Note that the environment of the mitochondria is similar to that of the cytoplasm due to the porins in the organelle (Similar pH of about 7)

• Allosteric Regulators can either decrease or increase the activity of an enzyme:

• Positive regulators increases activity

• Negative regulators decreases activity (i.e. reversible noncompetitive inhibition: “digitalis, which blocks the activity of Na+-K+ ATPase and is used for the treatment of cardiac arrhythmia.”)

• An allosteric regulator could be a product that is made later in a pathway = Feedback Inhibition (this then slows the rate of the product being made) Ex. Feedback inhibition of glycolysis of ATP - ATP binds to the regulatory site which causes Phosphofructokinase activity to decrease, which is negative regulation which is caused by high ATP levels

• Positive regulation would be increasing PFK activity to combine ADP and Pi to make more ATP, which is caused by low ATP levels.

• Some allosteric regulators can turn “up” one reaction and turn “down” a different reaction (First command step: committed to make the first product of pathway)

DNA STRUCTURE & REPLICATION

• Central Dogma: DNA (Blueprint) > RNA (Intermediate) > Protein (Functional)

• Chromosomes (discovered in the 1940s) are composed of chromatin, which is a complex of DNA and protein. 

PEOPLE TO REMEMBER & THEIR DISCOVERIES

• Chargaff’s rules - the amount of A-T are equal, as well as the amount of C-G are equal to each other.

• Avery, MacLead, and McCarty - discovered that DNA is genetic material that controls how organisms develop

• Griffith - discovered that biochemical genetic material can transform bacterial cells

• Meselson & Stahl - confirmed that DNA is semiconservative

• Watson & Crick - DNA is a double-helical molecule

• Franklin & Wilkins - DNA has a uniform width of 2nm

• If a chain has “n” nucleotides, it has 4^n possibilities

• Strands will be separated at the ori and will be replicated away from the ori

• Helicase unwinds the DNA > causes tension that is relieved by Topiosomerase that works ahead of the replication fork

• Eukaryotes don’t use topoisomerase due to linear strands

• HOWEVER: Eukaryotes, Prokaryotes (Bacteria), and Archaea all have circular DNA

• Single Strand Binding Proteins hold the strands apart/keep them from coming back together long enough to get the machinery in there

• dNTP added to the 3’ end (3’ OH group) using two phosphates that will be broken off

• Leading strand - continuous and uninterrupted

• Lagging strand discontinuous; leads to okazaki fragments

• DNA Poly III (DNA-dependent, DNA-synthesizing) requires a RNA primer (primase; DNA-dependent, RNA-synthesizing enzyme) as it can only add to a free 3’ OH group of a NTP (RNA Poly does NOT)

• RNA nucleotides are removed by DNA Poly I and replaced with DNA nucleotides, closing the gaps but not nicks. Nicks are “filled” by DNA Ligase that helps add the phosphodiester bonds between the nucleotides using ATP

• Nuclease - an enzyme that hydrolyzes a phosphodiester linkage

• Exonuclease - an enzyme that hydrolyzes nucleic acids from the end of a chain

• Can be 5’-3’ or 3’-5’ exonucleases

• Ex. DNA polymerase I's ability to remove primers is due to its 5'–3' exonuclease activity, which is a separate enzymatic activity from its DNA synthesizing ability

• Ex. Proofreading is 3’-5’ exonuclease activity

• Endonuclease - “within”; a nuclease that hydrolyzes nucleic acids internally

• No directionality

• Telomerase (RNP: RNA + Protein components) extends unreplicated end (parental) using its own internal RNA template

• Topoisomerase can also “supercoiled” circular DNA > more tightly packed and less likely to get damaged this way (In Bacteria)

• Histones - (H1, H2A, H2B, H3, and H4) are small, positively charged proteins which allows it to bind to DNA since it’s phosphate groups are negatively charged (In Eukaryotes)

• Bacteria DON’T have histones but Archaea DOES

• Core nucleosomes:

• 2 of each histone proteins, excluding H1 > 2 H2A, 2 H2B, 2 H3, and 2 H4

• 146 (or 147) base pairs of DNA > wrapped approx. 2 times around histones

• Packing of DNA & Histones into nucleosomes yields chromatin fiber of approx. 10 nm diameter

• Structure: consists of 2 of each histones, linker DNA which links histones together, and nucleosome “bead” that has 8 histones and 146/7 base pairs of DNA

• Chromatosome structure - a nucleosome plus a single molecule of H1 > holds nucleosomes together

• 10 nm folds into 30 nm fiber (zig zag or solenoid)

• Interphase Chromatin:

• Euchromatin “excessible” that exist in loosely condensed form (DNA that has been unwound and is distributed throughout the nucleus)

• Heterochromatin “inaccessible” highly condensed form (found at periphery of nucleus > near inner nuclear membrane)

• 30–nm fibers condense to mitotic chromosomes

TRANSCRIPTION & TRANSLATION

• Transcription - carried out by DNA-dependent, RNA-synthesizing molecule of RNA polymerase which does NOT need a primer

• STEPS:

1. Promoter region

2. Initiation

3. Elongation

4. Termination

• RNA polymerase in E coli consist of 6 subunits that make up the HOLOENZYME

• α2ββ′ωσ (without σ subunit: called core enzyme)

• Looks for discrete regions of DNA to transcribe to RNA (not entire genome)

• Promoter sequences are at -10 site (TATAAT sequence) or -35 site (TTGACA sequence) > these sites are conserved and consensus

• The better the consensus sequence, the easier it is for RNA polymerase to recognize and bind to it

• The sigma subunits acts as the “feet” as it searches for the “slippers” that are the promoter sites

• When RNA Poly moves from left to right (downstream) the bottom strand (3’ to 5”) is the template strand; when it moves from right to left (upstream) the top strand is the template strand so that the RNA is synthesized antiparallel 5’-3’

• Termination:

• In E. coli it uses Rho (p) dependent termination or intrinsic termination

• Rho (p) binds to RNA and transcription complex and goes to the 3’ end which pulls RNA off and RNA polymerase dissociates from DNA

• Intrinsic termination utilizes self-complementary sequences that lead to harpin-loop (G-C rich) that spontaneously forms and pushes RNA poly away

• All genes are transcribed by RNA polymerases

• One RNA polymerase in Bacteria

•  Holoenzyme includes σ subunit; Core Enzyme does not

• Three RNA Polymerases in Eukaryotes:

• RNA Poly I - transcribes rRNA

• RNA Poly II - transcribes mRNA

• RNA Poly III - transcribes tRNA; some RNA

• Each has/recognizes its OWN promoter

• Eukaryotic RNA polymerases have no sigma factors, and only weakly associate with DNA

• Eukaryotes require regulatory proteins called transcription factors (TFs)

• Spacer DNA - non coding genes between genes

• Introns - non coding genes within a gene

• Exons - coding regions within a gene “expressed”

• mRNA Processing:

• Occurs post-transcriptionally but concurrently, meaning that RNA poly has moved past the region but transcription is still occurring 

• Has to be completed before mRNA is moved to the cytoplasm

• snRNPs: small nuclear RNA molecules and proteins that precisely remove introns and join ends of exons in the process of splicing (Inaccurate splicing can lead to > Thalassemias (defective hemoglobin))

• Invariant Adenine base always located in introns so splicing can bind to it and undergo

• Alternative splicing can mix around the different exons as long as important/mandatory exons are used (This can be used to explain the complexity of humans as the human genome consist of about only 21,000 genes)

• 5’ cap is added to mRNA as the maintained nucleoside triphosphate loses a phosphate by RNA 5’-triphosphatase and then GTP is oxidized into GMP which is joined to the nucleoside diphosphate, finally a methyl group (CH3) is added. Overall 5’ cap adds stability to the mRNA, identification for translation, and protects mRNA from degradation

• 3’ Poly A tail is added to mRNA by Poly-A polymerase which adds about 200-300 adenine nucleotides. Adds temporary stability to protect it against degradation, also aids in allowing multiple copies of proteins to be made from a single eukaryotic mRNA

• Translation - mRNA to Protein that occurs in the cytoplasm

• 3 nucleotides per amino acid is the minimum number to account for the 20 amino acids we already know about > Codons (64 total; 3 of which are stop codons)

• Genetic code is:

• Degenerate/Redundant: most amino acids are coded for by more than one codon

• Unambiguous: given codon never codes for more than one amino acid

• Non Overlapping: ribosome locks one codon and moves onto the next codon

• tRNAs acts as bridges between amino acids and mRNA (Intrastrand base pairing causes it to fold on itself 

• ACC sequence is the amino acid attachment site

• The anticodon, 3’-5’ (complementary to codon, 5’-3’ of mRNA) is located on the bottom of tRNA molecule

• Binding of amino acid to tRNA is SPECIFIC and requires energy via the hydrolysis of ATP which leads to the covalent bond between amino acid and tRNA > Amino acid covalently bonded to 3’ end (OH) of Adenine base at amino attachment site

• Aminoacyl tRNA synthetases: “charges” reaction of tRNA via attachment of amino acid (different aminoacyl tRNA synthetases for each amino acid)

• Each enzyme recognizes both “ends” of tRNA, which enables it to identify if this is a tRNA that it is “allowed” to add its amino acid to 

• Ribosome: site of protein synthesis and are ribonucleic protein complexes which consists of rRNA and proteins

• Prokaryotic ribosome - 70S which has 50S+30S subunits which consist of 5S, 23S, 16S rRNA

• Eukaryotic ribosome - 80S which has 40S+60S subunits which consist of 5S, 5.8S, 28S, 18S rRNA

• The subunits “tucks together” when coming together

• Initiation of Translation:

• Small ribosomal subunit, recognition of start codon (AUG) which is fMet in prokaryotes and unmodified Met in eukaryotes

• Archaea has fMet as its start codon, similar to prokaryotes

• Accessory proteins (Initiation factors)

• Energy in the form of GTP

• Shine-Dalgarno or RBS: serves to align initiator AUG to with initiator tRNA

• Bacterial mRNA have multiple RBS which is why it can produce multiple proteins > polycistronic

• Eukaryotic mRNA only have one RBS which is why they are monocistronic

• Elongation: follows initiation

• Binding of charged tRNA: In bacteria, Large subunit joins small subunit as fMet rest in the P site (never was in A-site to begin with)

• Peptide bond formation: Elongation factors attached to a GTP are all attached to charged amino acids. Elongation factor separates amino acid from polypeptide chain to ensure that it is the correct amino acid before forming a peptide bond. It is then released after correct codon-anticodon pairing and GTP is hydrolyzed and used as energy. Formation of a peptide bond is endergonic and it bonds the C-Terminus end of the first amino acid to the N-Terminus end of the new/incoming amino acid. This process is done by Peptidyl Transferase in the ribosome active site as the bond is broken to free up the carboxyl group in the first amino acid in the P site and now the hydrolyzed GTP can be used to form peptide bond.

• Translocation: Requires another Elongation factor and the energy stored from GTP to move the ribosomes > P to E site and A site to P. The “ejected” tRNA can be recharged and used again

• Repeated until stop codon is reached:  Release factors recognize stop codons, as they are proteins that have a 3D shape that is compatible with the stop codon and resembles charged tRNA molecules, thus breaking the high energy bond between protein and tRNA. (tRNA transferase breaks bond of amino acid in p site and since it has no new amino acid to bond to, due to release factor, mRNA and the polypeptide is released and the ribosome subunits fall apart 

• Assembly-line style production of mRNA is called a polysome or polyribosome: this is when there are multiple ribosomes simultaneously making proteins on a single strand of mRNA

• In Prokaryotes, transcription and translation can occur simultaneously

CREATED PROBLEMS, QUESTIONS, and TIPS WITH ANSWERS

Here are some questions based on your study notes. The answers are provided at the bottom so you can test yourself before checking them.

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### Cellular Respiration

#### Free Response

1. Explain the role of NADH and FADH2 in the electron transport chain.  

The role of NADH and FADH2 in the electron transport chain is to serve as electron carriers, which NADH drops off its electrons at complex I and gets oxidized back into NAD+ and FADH2 drops its electrons off at complex II (not a transmembrane complex, so it doesn’t contribute to the H+ concentration gradient) and gets oxidized back to FAD. The electrons dropped off cause catalytic reactions within complexes that lead to proton pumps actively transporting H+ ions into the intermembrane space that will then flow through ATP synthase.

2. What is chemiosmosis, and how does it contribute to ATP synthesis?  

Chemiosmosis is the concentration gradient created with H+ ions that creates a high level of H+ ions in the intermembrane space and a low concentration of H+ ions in the matrix, and naturally things want to go from high concentration to low concentration which is why the H+ ions naturally flow through ATP synthase, in which proteins spin and bring together ADP and Pi to create ATP, which is the ultimate goal of cellular respiration.

3. Compare and contrast aerobic respiration and anaerobic respiration in terms of ATP production.  

Aerobic respiration creates more ATP per glucose molecule while anaerobic respiration (fermentation) creates more ATP per unit of time.

#### Problem-Solving

4. If a cell undergoes glycolysis but lacks functional mitochondria, what will happen to the pyruvate molecules produced?  

Fermentation will occur producing lactate

5. If a mutation prevents ATP synthase from functioning, how would that affect cellular respiration?  

If a mutation prevents ATP synthase from functioning, then no ATP would be produced from the Electron Transport Chain via oxidative phosphorylation, and less water would be made as a byproduct. There would be an influx of ATP in the intermembrane space.

#### Multiple Choice

6. Which process produces the most ATP?  

   a) Glycolysis  

   b) Krebs Cycle  

   c) Electron Transport Chain  

   d) Fermentation  

7. What is the final electron acceptor in the electron transport chain?  

   a) NAD+  

   b) Oxygen  

   c) ATP  

   d) Carbon dioxide  

8. Which of the following statements is TRUE about fermentation?  

   a) It produces more ATP than aerobic respiration.  

   b) It regenerates NAD+ to allow glycolysis to continue.  

   c) It requires oxygen to function.  

   d) It takes place in the mitochondria.  

#### Fill in the Blank

9. During glycolysis, a 6-carbon glucose molecule is broken down into two pyruvate__ molecules.  

10. The enzyme ____topiosomerase___ unwinds DNA ahead of the replication fork.  

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### DNA Structure & Replication

#### Free Response

11. Describe the role of topoisomerase in DNA replication.  

Topoisomerase relieves the tension created by Helicase ahead of the replication fork in circular DNA in prokaryotes (E. coli for example).

12. Explain how DNA polymerase III contributes to the accuracy of replication.  

DNA Poly III adds dNTPs at the end of a free 3’ OH group of a RNA primer (primase) and does it quick

#### Multiple Choice

13. Which enzyme removes RNA primers and replaces them with DNA nucleotides?  

   a) DNA polymerase I  

   b) DNA polymerase III  

   c) Helicase  

   d) Ligase  

14. What type of bond connects nucleotides within a single strand of DNA?  

   a) Hydrogen bond  

   b) Peptide bond  

   c) Phosphodiester bond  

   d) Ionic bond  

#### Fill in the Blank

15. The ___leading___ strand is synthesized continuously, while the ___lagging___ strand is synthesized in fragments.  

16. ____SSBPs____ prevents single-stranded DNA from reannealing during replication.  

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### Tricks & Tips for Memorization

✅ **Glycolysis, Krebs, ETC Order:** “Good Kids Eat” (Glycolysis → Krebs → Electron Transport Chain)  

✅ **ATP Yield by Process:** Glycolysis (2 ATP), Krebs (2 ATP), ETC (~32 ATP) → Remember "2, 2, 32"  

✅ **Lagging vs. Leading Strand:** "Lagging Lags" because it has to wait for fragments to form  

✅ **Purines vs. Pyrimidines:** "Pure As Gold" (A & G are Purines), "Cut The Pyramid" (C, T are Pyrimidines)  AT2/CG3

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### Answers (Check after answering!)

1. NADH and FADH2 donate electrons to the ETC, helping pump protons across the membrane and drive ATP synthesis.  

2. Chemiosmosis refers to the movement of protons back across the membrane through ATP synthase, generating ATP.  

3. Aerobic respiration produces more ATP per glucose molecule, while anaerobic respiration is faster but less efficient.  

4. Pyruvate will undergo fermentation, leading to lactate (in animals) or ethanol (in yeast).  

5. ATP production will stop, leading to cell energy failure.  

6. c) Electron Transport Chain  

7. b) Oxygen  

8. b) It regenerates NAD+ to allow glycolysis to continue.  

9. Pyruvate  

10. Helicase  

11. Topoisomerase relieves the tension in DNA caused by unwinding.  

12. DNA polymerase III proofreads and corrects errors in the newly synthesized strand.  

13. a) DNA polymerase I  

14. c) Phosphodiester bond  

15. Leading, Lagging  

16. Single-strand binding proteins (SSBPs)  

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### Transcription & Translation

#### Free Response

17. Describe the key differences between prokaryotic and eukaryotic transcription.  

Prokaryotic transcription can happen simultaneously with transcription in the cytoplasm of cell and is polycistronic, while transcription in eukaryotes happen in the nucleus of cell and has to finish completely before translation can occur in the cytoplasm, and is monocistronic.

18. Explain the role of the sigma factor in bacterial transcription.  

The sigma factor is a part of the holoenzyme and its role is to find the promoter regions and fit onto them perfectly so RNA polymerase is properly attached to the DNA. Once attached and locked in RNA poly begins transcription and the sigma factors disassociate.

19. How does the 5’ cap and poly-A tail contribute to mRNA stability in eukaryotes? 

5’ cap provides identification for the initiation of translation, as well as stability and protection against degradation, while the Poly-A tail provides temporary stability and protection against degradation and provides insight on translation termination. 

20. What is alternative splicing, and how does it contribute to protein diversity?  

Alternative splicing is when exons are assorted in different ways, as long as the mandatory exons remain to create different types of mRNAs which become different types of proteins which explains why humans are so complex due to their protein diversity.

#### Problem-Solving

21. A mutation occurs in the promoter region of a eukaryotic gene, making it unrecognizable to transcription factors. What effect will this have on gene expression?

Eukaryotes do not have promoter regions, only in prokaryotes  

22. If a tRNA molecule has the anticodon 3’-UAC-5’, what mRNA codon will it pair with, and what amino acid will it carry?  AUG - Methionine 

#### Multiple Choice

23. Which enzyme is responsible for synthesizing RNA from a DNA template?  

   a) DNA polymerase  

   b) RNA polymerase  

   c) Helicase  

   d) Ligase  

24. In eukaryotic cells, which RNA polymerase transcribes mRNA?  

   a) RNA polymerase I  

   b) RNA polymerase II  

   c) RNA polymerase III  

   d) Reverse transcriptase  

25. Which process occurs in the cytoplasm in eukaryotes?  

   a) Transcription  

   b) Translation  

   c) RNA splicing  

   d) Polyadenylation  

26. What is the purpose of the Shine-Dalgarno sequence in prokaryotic mRNA?  

   a) It signals the end of transcription.  

   b) It helps ribosomes recognize and bind to the mRNA.  

   c) It codes for the start codon.  

   d) It acts as a termination signal for translation.  

#### Fill in the Blank

27. The process of converting DNA into RNA is called transcription.  

28. The three-letter nucleotide sequence on mRNA that corresponds to an amino acid is called a codon.  

29. In prokaryotes, transcription and translation can occur simultaneously, whereas in eukaryotes, transcription occurs in the nucleus and translation in the cytoplasm.  

30. The enzyme responsible for attaching amino acids to their corresponding tRNA molecules is called aminoacyl tRNA synthetases.  

31. In prokaryotic translation, the first amino acid incorporated into the polypeptide chain is fMet, while in eukaryotic translation, it is unmodified Met__.  

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### Tricks & Tips for Memorization

✅ **Eukaryotic RNA Polymerases:** “Really Mean Teachers”  

   - RNA Poly I → rRNA  

   - RNA Poly II → mRNA  

   - RNA Poly III → tRNA  

✅ **Start Codon Mnemonic:** "AUG starts school in August" → AUG is the start codon.  

✅ **Stop Codons Mnemonic:** "U Go Away, U Are Annoying, U Are Gone"  

   - UGA → "U Go Away"  

   - UAA → "U Are Annoying"  

   - UAG → "U Are Gone"  

✅ Prokaryotic vs. Eukaryotic Transcription & Translation:  

   - Prokaryotes: Transcription and translation happen at the same time (polycistronic).  

   - Eukaryotes: Transcription happens in the nucleus, translation in the cytoplasm (monocistronic).  

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### Answers (Check after answering!)

17. Prokaryotic transcription occurs in the cytoplasm, has one RNA polymerase, and often processes multiple genes at once (polycistronic). Eukaryotic transcription occurs in the nucleus, involves three RNA polymerases, and mRNA undergoes modifications like capping and splicing.  

18. The sigma factor helps RNA polymerase bind to the promoter region in prokaryotic transcription.  

19. The 5’ cap helps ribosome recognition and prevents degradation, while the poly-A tail stabilizes mRNA and aids in translation.  

20. Alternative splicing allows different proteins to be produced from a single gene by rearranging exons.  

21. If the promoter is mutated, transcription factors cannot bind, so the gene will not be transcribed, leading to no protein production.  

22. The mRNA codon would be 5’-AUG-3’, coding for methionine (start codon).  

23. b) RNA polymerase  

24. b) RNA polymerase II  

25. b) Translation  

26. b) It helps ribosomes recognize and bind to the mRNA.  

27. Transcription  

28. Codon  

29. Simultaneously, cytoplasm  

30. Aminoacyl-tRNA synthetase  

31. fMet (formyl-methionine), Met (methionine)  

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### Scientists & Their Discoveries

#### Free Response

32. What did Avery, MacLeod, and McCarty discover, and why was their experiment important? 

They discovered that DNA is the genetic material of inheritance and not proteins 

33. How did Meselson and Stahl confirm that DNA replication is semiconservative?  

The did a Nitrogen isotope experiment, 14N and 15N (heavy nitrogen), and noticed after replication, DNA contained one new strand and one old strand, meaning that replication was semi-conservative

34. What was Griffith’s experiment, and how did it contribute to our understanding of genetic material?  

DNA can be used to transfer genetic information between bacteria

35. How did Rosalind Franklin’s work contribute to the discovery of DNA’s structure?  

DNA is 2nm wide due to the Purine-Pyrimidine bonds creating a double helical structure.

#### Problem-Solving

36. If Erwin Chargaff analyzed a DNA sample and found that 30% of the bases were adenine, what percentage of the bases would be cytosine?  

20% would be cytosine

37. If a scientist wanted to prove whether a newly synthesized DNA strand was built using the semiconservative model, what type of experiment could they conduct?  

Isotope Nitrogen experiment

#### Multiple Choice

38. Who discovered that DNA is the genetic material that determines an organism’s traits?  

   a) Watson and Crick  

   b) Avery, MacLeod, and McCarty  

   c) Meselson and Stahl  

   d) Griffith  

39. What did Griffith’s experiment with mice and Streptococcus pneumoniae demonstrate?  

   a) DNA is semiconservative.  

   b) Genetic material can transform living cells.  

   c) The shape of DNA is a double helix.  

   d) The number of A and T bases are always equal.  

40. Who used X-ray diffraction to determine the helical structure of DNA?  

   a) Watson and Crick  

   b) Rosalind Franklin  

   c) Erwin Chargaff  

   d) Meselson and Stahl  

41. Chargaff’s rule states that:  

   a) DNA is made of nucleotides.  

   b) DNA is replicated semiconservatively.  

   c) The amount of A = T and C = G in DNA.  

   d) RNA polymerase does not require a primer.  

#### Fill in the Blank

42. The scientist who discovered that the amounts of adenine and thymine in DNA are equal was Chargaff.  

43. The two scientists who built the first accurate double-helix model of DNA were Watson and Crick__.  

44. The experiment that demonstrated DNA replication follows a semiconservative model was conducted by Meselson__ and Stahl.  

45. The scientist who first demonstrated the transforming principle using bacteria was Griffth.  

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### Tricks & Tips for Memorization

✅ **Chargaff’s Rule Mnemonic:** "A T Cozy G" → A = T, C = G  

✅ **DNA Structure Scientists Mnemonic:** "Franklin Watched Crick's Model"  

   - Franklin → X-ray diffraction  

   - Watson & Crick → Built DNA model  

✅ **Griffith’s Experiment Mnemonic:** "Smooth Kills, Rough Chills"  

   - Smooth (S) strain = deadly  

   - Rough (R) strain = harmless  

   - Heat-killed S + R = deadly (transformation)  

✅ **Semiconservative DNA Replication:** "Semi = One Old, One New"  

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### Answers (Check after answering!)

32. Avery, MacLeod, and McCarty showed that DNA, not proteins, is the genetic material responsible for inheritance.  

33. Meselson and Stahl used nitrogen isotope labeling in DNA to show that each new DNA molecule contained one original strand and one new strand.  

34. Griffith’s experiment showed that a "transforming principle" (later identified as DNA) could transfer genetic information between bacteria.  

35. Rosalind Franklin used X-ray diffraction to show that DNA had a helical structure with a uniform width of 2nm.  

36. If A = 30%, then T = 30%. That leaves 40% for G and C, meaning C = 20%.  

37. A scientist could use nitrogen isotope labeling (like Meselson & Stahl) to track old and new DNA strands.  

38. b) Avery, MacLeod, and McCarty  

39. b) Genetic material can transform living cells.  

40. b) Rosalind Franklin  

41. c) The amount of A = T and C = G in DNA.  

42. Erwin Chargaff  

43. Watson and Crick  

44. Meselson and Stahl  

45. Frederick Griffith