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Flashcards in nucleic acid and bioenergetics Deck (72)
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1
Q

Define Entropy

A

deltaS, measure of microscopic disorder in a system

2
Q

Define Enthalpy

A

deltaH, measure of energy of a thermodynamic system

3
Q

Define Gibbs Free Energy

A

deltaG, Amount of work that can extracted from a system, deltaG =deltaG0 + RT ln [PRODUCTS]/[REACTANTS]

4
Q

Define high energy componds

A

Compounds that store chemical energy in their bonds, which can be accessed for work on other compounds with rela.ve ease.

5
Q

Name some high energy compounds

A

ATP, Glucose, NADH

6
Q

Define free energy

A

The change in Gibbs free energy is the maximum work that a process can perform under constant pressure. A nega.ve Gibbs free energy suggests a reac.on or process is thermodynamically favorable and will occur spontaneously since the products are stable_

7
Q

What is a Redox reaction?

A

A chemical reaction in which atoms have their oxidation state changes (i.e. the exchange of electrons between atoms or compounds) deltaG’o = -nF deltaE’o where deltaE’o = E’o electron acceptor - E’o electron donor in volts, n is number of electrons transferred, Positive deltaE’o corresponds to negative deltaG’o

8
Q

How to convert from cal to joules

A

1 cal = 4.184 joules.

9
Q

Define redox potential

A

Reduction potential E is a measure of the readiness with which an atom or molecule accepts an electron relative to H+. The
more positive the value of E, the more a molecule likes to accept electrons. The more negative the value of E the more it likes to donate electrons. Reduction potential E is measured in volts (V).

10
Q

Electron flow in biological systems

A

In cells, glucose is a major source of electrons and O2 is the final electron acceptor. As electrons pass from compounds with low to high E free energy is released The resulting electromotive force (emf) is used to make high energy compounds ATP, NADH, and NADPH that are used to do biological work.

11
Q

Define First Law of Thermodynamics

A

Energy is always conserved (i.e. energy cannot be created or destroyed)

12
Q

Define Second Law of Thermodynamics

A

The entropy of the universe if always increasing (i.e. it takes energy to put things in an orderly fashion)

13
Q

Define kinetic energy

A

Radiant (carried by photons from the sun), thermal mechanical, and electric energy (charged particles down gradients of electric potential)

14
Q

Define potential energy

A

Stored in chemical bonds, concentration gradients, electric fields from charge separation, and redox pairs

15
Q

What are the four ways that potential energy is stored?

A

Chemical bonds, concentration gradients, in redox pairs, in electric fields from charge separation

16
Q

What are the three basic thermodynamic equations?

A

deltaG =deltaG0 + RT ln [PRODUCTS]/[REACTANTS] or deltaG = 2.3RT log [C2] / [C1], deltaG0 = - RT lnKeq, deltaG = deltaH – T deltaS

17
Q

Define standad state free energy

A

deltaG0 = - RT lnKeq , the free energy change of a reac.on under standard condi.ons (298 K, 1atm, 1M, and pH=7), Keq= {[C][D]/[A][B]}

18
Q

If _G is negative which way does the reaction proceed?

A

Forward (i.e. the forward reaction is spontaneous), a nega.ve G is synonymous with a posi.ve Keq and both demonstrate that a reac.on at equilibrium favors the forma.on of products more than the reversion back to reactants.

19
Q

What does it mean when _G is zero?What does K equal at this point?

A

The reaction is at equilibrium K=1

20
Q

What is K when _G0 is positive?

A

K is less than 1, Keq = 10(-deltaG0/2.3RT)

21
Q

What equation does one use to relate Gibbs Free Energy to Redox potential

A

deltaG = -nFdeltaE Where n = number of electrons transferred, F = Faraday’s constant (96,500 C/Mol of e-), deltaE = difference in reduction potential in (volts), n= no. electrons transferred

22
Q

What might the system be doing if it is moving electrons?

A

Creating energy

23
Q

How might one make a reaction with a +_G move in the forward direction?

A

Couple it with a spontaneous reaction, deltaG3 =deltaG1 +deltaG2<0

24
Q

What are some high energy compounds used in biological systems?

A

Lipids and Carbohydrates

25
Q

What are the two main classes of high energy bonds?

A

Thioester (Sulfur - Carbon eg acetyl-Coa )High energy phosphate bonds (including phosphoanhydride e.g. ATP, phosphocreatine eg P-N, and phosphoenolpyruvate eg C-O-P)

26
Q

Examples of work done by cells

A

synthesis of molecules or other constitutes, cellular movements, transport of molecules against concentration gradient, generation of electric potential, and heat generation

27
Q

What are the major high energy compounds used to store energy

A

NADH, ATP, NADPH, and FADH2

28
Q

Which nitrogenous bases are purines? Pyrimidines?

A

Purines: AG Pyrimidines: CTU

29
Q

What is the difference between ribose and deoxyribose?

A

ribose has a hydroxyl group at the 2’ carbon and deoxyribose does not

30
Q

What is the difference between ribonucleoside and deoxyribonucleoside?

A

A ribonucleoside is a sugar (ribose) + base. A deoxyribonucleoside is doesn’t have a hydroxyl group at the 2’ carbon

31
Q

What is the difference between a nucleoside and nucleotide?

A

A nucleotide has a 5’ phosphate group, a nucleoside does not

32
Q

What is the difference between a nucleoside diphosphate and nucleoside triphosphate?

A

Nucleoside triphosphate (ATP) has three phosphate groups, nucleoside diphosphate (ADP) has two phosphate groups

33
Q

What are the non-specific vs. specific drug targets in the central dogma

A

In rapidly deviding cells (eg foreign cells and cancer), non-specific targets include inhibiting DNA replication, transcription, and translation. A more specific target are proteins

34
Q

Rank the relative solubilities of bases, nucleotides, and nucleoside; Pyrimidines vs. Purines

A

More hydrophobic, less soluble in water. Purine is less soluble than pyrimidine. Base is less soluble than nucleoside. Nucleoside is less soluble than nucleotide.

35
Q

What are the classes of RNA in human cells?

A

Structural RNAs (rRNA, rRNA), regulatory RNAs (miRNA, siRNA) information containing RNAs (mRNA)

36
Q

examples of nucleotides not in DNA or RNA

A

coenzyme A, cAMP, cGMP, and NAD

37
Q

What is an example of a disease caused by the insolubility of bases?

A

Gout - An accumulation of uric acid in joints as a precipitate of purines of low solubility

38
Q

What makes DNA and RNA polar?

A

The 3’ hydroxyl group and the 5’ phosphate group. Nucleotides are always added to the 3’ prime end b/c it is nucleophilic. Nothing is ever added to the 5’ prime end.

39
Q

Define phosphodiester linkage.

A

The key to the DNA/RNA backbone. Caused by the nucleophilic 3’ hydroxyl group attacking the 5’ phosphate group.

40
Q

What critical experiment helped establish DNA as the basic genetic material?

A

Avery, McCarty, and McCloud:Isolated DNA from virulent bacteria. Inserted into non-virulent bacteria. Kills the mouse.

41
Q

List Chargaff’s Rules.

A

C=G, A=TC - Cytosine, G - Guanine, A - Adenine, T - Thymine

42
Q

Describe the Watson-Crick model for DNA structure

A

Double stranded sugar-phosphate backbone. Internal base pairing (Chargaff’s Rules). Anti-parallel to one another (5’ to 3’ and 3’ to 5’). Geometry strongly favors A-T and G-C base pairs only. Suggested a molecular mechanism for replication of the genetic material.

43
Q

What is the major groove? Minor groove?

A

DNA has two grooves, the major is bigger, minor is smaller.

44
Q

What four things affect the stability of DNA double helix structure in solution?

A
  1. [salt], higher [salt] = more stable2. Extremes of pH destabilize3. Length, longer strand = more stable4. GC/AT ratio, higher ratio = more stable GC has 3 hydrogen bonds, AT has 2
45
Q

Describe linear, circular, relaxed and supercoiled forms of DNA.

A

Linear = non circular dna (eurkaryotic)Circular = found in prokaryotes (ecoli)Relaxed = straight ribbon with normal twistingSupercoiled = DNA with torsion applied (important for eukaryotes)

46
Q

What is methylation (with regard to DNA) and how does it lead to disease?

A

When there is a C; G adjacent to one another on same side of helix the C is usually methylated = 5 methylcytosine (80-90% of time). Without such methylation such C-G areas are associated with gene promoters and can lead to over transcription of genes.

47
Q

What is deamination (with regard to DNA) and how does it lead to disease?

A

When a base loses an amine group mutations occur. W/o proper repair - leads to disease. For example C turns to U or When G is deaminated it becomes X which pairs with T. Then DNA repair converts X to A. Thus G-C has been converted to AT. Nitrous acid or nitrosamines can enhance the process of deamina.on and these substances are present in tobacco smoke.

48
Q

What is depurination (with regard to DNA) and how does it lead to disease?

A

The removal of a purine base from a deoxyribose sugar. Now missing base = no longer a nucleotide. Plus, this weakens the phosphodiester backbone of DNA. Repair is owen achieved by DNA repair enzymes.

49
Q

How does UV light damage DNA?

A

It covalently binds thymines together which distorts the helix and can block replication enzymes. Repaired by nucleo.de excision repair and TF2H.

50
Q

How do alkylating agents damage DNA?

A

nucleopholic attack of bases of nucleotides (eg mustard gas, cisplatin, a cancer drug) often contain benzene rings. alkylating agents are used as chemotherapeutics to damage the DNA of cancer cells, which then prevents proper DNA replication/transcription and thus cell growth.

51
Q

How do oxidative agaents damage DNA?

A

“reactive” oxygen free radical species generated in the mitochondria can damage DNA. Generally leads to -OH groups on bases, disrupting the DNA structure.

52
Q

How is DNA polymerized?

A

New nucleotides are added to the 3’ end.

53
Q

How are nucleoside analogues used as drugs?

A

When the cell is replicating DNA the free floating analogues are recruited to the new strand. Their structure, however, causes the new strand to be nonfunctional.

54
Q

What is AZT

A

example of nucleoside drug that inhibits DNA synthesis, has no 3’ hydroxly group, hence HIV can not be replicated by reverse transcriptase

55
Q

Differences between DNA and RNA?

A

DNA has no 2’ Hydroxyl group.RNA binds Uracil instead of ThymineRNA is single stranded

56
Q

What are the 3 main classes of RNA and their components?

A

Information containing: mRNA (messenger)Structural: rRNA (ribosomal), snRNA (small nuclear)Regulatory: miRNA (micro), siRNA (small interfering)

57
Q

What does rRNA do?

A

Ribosomes are made of rRNA. Ribosomes translates mRNA.

58
Q

What does snRNA do?

A

Small nuclear RNA helps with splicing, regulation of transcription factors, and maintenance of telomeres.

59
Q

What do miRNA and siRNA do?

A

They regulate gene expression.

60
Q

What does mRNA do?

A

Contains information (codons) to translated into proteins by ribosomes (rRNA).

61
Q

Describe the chemical basis for nucleic acid melting. How can it be used to detect one specific sequence in total cellular DNA?

A

Heating up the DNA breaks the H-bonds between the strands (base pairs)Add tagged probe of 20-25 base pairs which will anneal onto a strand if they have the complementary sequence.

62
Q

What creates the stability of DNA

A

Stacking energies (hydrophobic interactions) between adjacent base pairs and H-bonding between complementary bases in a base pair are both important for the stability of DNA to help compensate for negatively charged phosphates

63
Q

how can nucleoside analogues are used as drugs?

A

Nucleoside analogs can be used as drugs because analogs can become incorporated, or intercalated into the DNA which can create changes to the shape of the DNA or changes to the DNA’s ability to be read and replicated.

64
Q

Explain how puromycin mimics amino-acyl tRNA to terminate translation.

A

an antibiotic that mimics the “acceptor” 3’ end of a tRNA that is charged with an amino acid. Puromycin can bind in the ribosome as it is translating and covalently attach to a growing polypeptide chain, preventing the completion of translation. The Streptomyces species that makes puromycin also makes an enzyme that inactivates the antibiotic inside the bacteria. This enzyme modifies the part of puromycin that is involved in covalent attachment to the polypeptide chain, rendering puromycin inactive.

65
Q

What are topoisomerases?

A

Are enzymes that regulate the overwinding or underwinding of DNA. The winding problem of DNA arises due to the intertwined nature of its double-helical structure. For example, during DNA replication, DNA becomes overwound ahead of a replication fork. If left unabated, this tension would eventually halt DNA replication. (same with transcription.) They bind to either single-stranded or double-stranded DNA and cut the phosphate backbone of the DNA. Is very important for DNA replication so is a good drug target for cancer cells

66
Q

What are the major similarities and differences between DNA and RNA

A

RNA has an additional OH group at the 2’ carbon in the ribose sugar ring. RNA uses uracil instead of thymine. RNA is far more easily hydrolyzed than DNA due to nucleophilic attack by 2’ OH on the phosphodiester bond. RNA is single stranded unless it complementarily binds to itself forming hairpin loops. DNA has no OH group at 2’, is double stranded, and uses Thymine to bind to Adenine on the complementary strand.

67
Q

what are the implications of the structural difference of riboculceotide?

A

RNA is far more easily hydrolyzed than DNA due to nucleophilic attack by 2’ OH on the phosphodiester bond, The labile nature of RNA allows the cell to readily reduce the levels of an RNA by stopping its transcription and allowing the existing molecules to degrade. This can have profound implications for the speed of changes in gene expression.

68
Q

Cisplatin

A

base alkylating agent, interfere with DNA structure and replication

69
Q

Actinomycin D

A

a naturally occurring antibiotic that has also been used as a chemotherapy. “Intercalates” into DNA (inserts a ring structure that can stack with DNA bases) and alters the double-helical structure. Interferes with DNA replication and transcription. interfere with DNA structure and replication

70
Q

Doxorubicin

A

similar intercalator to Actinomycin D. Interferes with DNA replication. interfere with DNA structure and replication

71
Q

Etoposide and Camptothecin

A

are chemotherapeutics that target topoisomerases that relax DNA supercoiling (super-twisting of the double-helix). Topoisomerases are necessary during DNA replication to avoid supercoiling as the double helix is opened up to copy the strands. Topoisomerases must break the DNA backbone to “relax” supercoiled DNA. Drugs that interfere with this process usually leave DNA breaks that cannot be repaired. interfere with DNA structure and replication

72
Q

What are the implications of RNA 3D structure?

A

When not constrained by helix formation RNA can assume many conformations due to rotation around many bonds. Confers structural capacity approaching that of proteins