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Flashcards in Week One Objectives Deck (73):
1

What is the chemical make-up of nucleic acids

Nitrogenous Base, Ribose sugar, phosphate (deoxyribose in DNA lacks 2' carbon hydroxyl group

2

Watson-Crick Base Pairing

A goes with T (or U)- 2 Hydrogen bonds G goes with C- 3 Hydrogen bonds

3

Compare/Contrast Eukaryotic and Prokaryotic genomes

Pro circular, Euk linear Pro is tightly coiled, Euk is compacted via histones

4

What is the semi-conservative model of DNA replication and why is it important for inheritance?

As DNA is replicated a daughter strand is paired with a parental strand (always one old and one new)- this is the way DNA replication ensures duplication of genetic info is passed on

5

Describe how properties of A.A. affect protein structure

Properities of A.A. (hydrophobicity, polarity, h-bonding ability, etc) affect folding

6

Primary Structure of Proteins

Amino acids covalently linking through peptide bonds

7

Secondary Structure of Proteins

Alpha helices, and Beta sheets: form due to hydrogen bonding of backbone (not R groups)

8

Tertiary Structure of Proteins

interaction of R groups of helices and beta sheets (ion, hydrogen, dipole-dipole, disulfide bridges), can have multiple ways to fold but usually results in lowest energy state

9

Quaternary Structure

interaction of multiple domains/ tertiary structures

10

What are some post-translational modifications?

addition of: sugar carbs lipids phosphates acytl group

11

What do catalysts do to reactions?

lower activation energy to increase the RATE of reaction DOES NOT CHANGE DELTA G (net energy change of reactants to products does not change)

12

How does substrate and product concentration affect reactions?

Energetically: removing products or adding reactant will make the forward reaction more favorable (makes delta G more negative) Kinetically: increasing [substrate/reactant] will increase rate of rxn

13

Allosteric activators

-don't compete with substrate binding site -increasings affinity for substrate -lowers Km (makes enzyme more active) -can increase Vmax

14

Allosteric inhibitors

-binds at place other than the active site -decreases affinity for substrate -increases Km (makes enzyme less active) -can lower Vmax

15

Competitive inhibitors

-compete for substrate-binding site in catalytic cleft -prevents substrate from binding -transient interaction :increasing amount of substrate can overcome competitive inhibitor, therefore DOES NOT AFFECT Vmax -Km is INCREASED (need more substrate to get to Vmax)

16

Non competitive inhibitors

typically binds at catalytic site (ADPspot)/active site, makes COVALENT bond with enzyme CANT OVER COME -Km DOES NOT CHANGE -decreases Vmax

17

Benefits of enzymes on runs

-lowers activation energy -provides proximity and orientation of reactants -ensures specificity -stabilizing transition complex -can couple energetically unfavorable rxns with favored ones

18

What is Vmax?

maximum reaction rate at an infinite substrate concentration (where all enzyme is bound to substrate)

19

Km

Michaelis constant- concentration of substrate at half of Vmax

20

1. Describe the components of the eukaryotic DNA replication complex and their functions

•DNA polymerase- enzyme in replication, copies parental template strand in 3’ to 5’ direction, producing new strands 5’ to 3’ •Primase- makes a RNA primer so DNA polymerase has free 3’ hydroxyl group •SSB Proteins- prevent strands from re-associating and protect them from enzymes that cleave single stranded DNA •Topoisomerases 1- enzymes that break/nick phosphodiester bonds and rejoin them to relieve supercoiling tension •Topoisomerase 2- DNA-helix-passing reaction •Ligase- joins two polynucleotide chains together

21

2. Describe the molecular mechanisms by which eukaryotic cells prevent their genomes from becoming shorter with each cell division, and how this process contributes to normal aging and cancer

• Telomerase adds short piece of DNA (called a telomere) that is lost when cell divides and DNA is replicated • Without this cell progeny will reach Hayflick limit and commit suicide • Aging= somatic cells express telomerase at low levels and decrease expression with time

22

Describe the structure of a gene, identifying the relative locations and functions of promoters, enhancers, transcriptional start site, introns and exons.

•Promoter (typically upstream of start point) control binding of RNA pol to DNA and identifies the start site and frequency of transcription •Enhancer Frequency of transcription is controlled by cis regulatory sequences (same strand), all regulatory sequences interact with trans-acting proteins that assist in binding and stability of RNA pol •Transcriptional Start Site •Intron/Exons – introns are taken out, exons are spliced together to make protein product

23

4. Compare transcription in prokaryotes and eukaryotes.

Prokaryotic Eukaryotic Transcription occurs is CYTOPLASM Transcription occurs in NUCLEUS Polymerase (with help of sigma) is able to initiate transcription without help of other proteins Requires large set of proteins that must assemble at promoter before RNA Pol can being transcription Core and regulatory elements are adjacent Core and regulatory elements can be VERY far apart Polycistronic (more than one “gene” on mRNA) Cistronic (each mRNA contains only one “gene) Translation of mRNA begins prior to transcription termination (no post transcriptional modifications) Transcription terminates before translation begins (need 5’ cap, Poly A tail, and splicing to occur) No Histones DNA needs to be “unpacked” prior to transcription

24

Understand the functions, structures, and synthesis of mRNAs, tRNAs, rRNAs, and miRNAs and lincRNAs

• mRNAs- messenger RNA, precursor for protein synthesis • rRNAs- ribosomal RNA, form ribonucleoprotein complexes • miRNAs- small non-coding RNAs, used for other cell processes like regulation • lincRNAs- non-coding RNAs, known functions: gene silencing by affecting chromatin formation or by antisense

25

Describe relationship between DNA coding strand, DNA template strand, and mRNA

coding strand is compelmentary to template strand, mRNA is complementary to template strand but T's turn into U's

26

Transcription in prokaryotes

1.RNA polymerase holoenzyme forms (core pol plus sigma) 2.RNA pol and Sigma Factor bind to promoter, causing DNA strands to unwind and separate 3.Sigma Factor is release at approx. 10 nucleotides 4.Elongation continues until RNA pol finds termination signal a. Hairpin loop b. Binding of protein Rho c. Note- termination signals are encoded in DNA and many function by forming RNA structure that destabilizes pols grip on RNA

27

Transcription in Eukaryotes

1. transcription factors bind promoter and help RNA pol bind 2. Other factors and RNA pol assemble at promoter 3.TFIIH opens helix, looses transcription factors 4. Elongation factors associate 5. topoisomerases relieve tension in supercoiling 6. Addition of 5' cap 7. Addition of 3' poly A tail 8. Introns are spliced out, exons put together 9. mRNA is bound to proteins that stabilize and transport through nuclear pores in cytosol

28

What are the size of rRNAs?

45S is cleaved to produce 18S, 28S, 5.8S

29

Given a wild type mRNA sequence, apply an understanding of the codon structure of mRNAs to predict changes in protein structure due to a specific mutation

If there is a mutation that would change the amino acid pair with that codon, it will change the folding of the resulting protein

30

Describe the structure and variation in the genetic code

• 64 three nucleotide codons in mRNA encode for 20 amino acids, plus translation start and stop signals; most amino acids have multiple codons; codons are read 5′ to 3′ with the 5′ terminal nucleotide at the left

31

Describe the structure and function of tRNAs in the process of translation

• tRNAs have clover leaf type structure with two critical spots 1. Anticodon- 3 consecutive nucleotides that pairs with the complementary codon on the mRNA 2. Short single stranded region on 3’ end which recognizes and binds to specific amino acids that correspond to the codon • tRNAs are responsible for pairing the correct amino acid with the correct codon of the mRNA sequence

32

Understand wobble base pairing (will be on USMLE!)

• Tolerate mismatch at third position- tRNAs are constructed so that they require accurate base pairing only at the first two positions of the codon

33

5. Describe how mRNAs are translated to proteins, including the molecular mechanisms of initiation, elongation, and termination

• Initiation- eIFs put initiator tRNA into small ribo subunit, small subunit binds mRNA at 5’ end, goes until finds AUG, eIFs dissociate and allow large ribo subunit to bind • Elongation- New tRNA is put in A site, growing chain in P site, “empty” tRNA is E site, high energy bond broken between tRNA and AA, and energy put towards making new peptide bond (elongation factors drive rxn forward) • Termination- Signaled by stop codons (UAA, UAG, UGA), tRNA doesn’t recognize those and signals ribosome to stop translating

34

6. Compare eukaryotic and prokaryotic translation, and describe the targets of antibiotics that target translation.

• Similar process • prokaryotic translation can occur during transcription (eukaryotic can’t) • Ribosome sizes are different • Prokaryotic ribosomes don’t need a 5’ cap to begin translation

35

What does 2,3-BPG do? and what happens to the oxygen saturation curve?

2,3 BPG decreases hemoglobins affinity for oxygen by altering its structure, shifting curve to right

 

 

 

36

Glycosylation of hemoglobin

noenzymatic, irreversible glycosylation related to amount of hemoglobin related to amount of glucose in blood (can cause aggregation)

37

Sickle cell anemia vs disease vs. carrier

Sickle cell allele has valine at position 6 in beta chain Anemia- HbSS Carrier- HbSA Disease- HbS[not S or A] *more aggregation occurs in deoxygenated state

38

Why would a patient with sickle cell anemia present with jaundice?

-sickled hemoglobin results in a lot of hemolysis -liver needs to work harder produces excess bilirubin -liver is not able to excrete bilirubin

39

How does pH affect the protonated state of an "R" group and an A.A.?

if pH < pKa is acidic form (protonated)

if pH > pka is basic form (deprotonated)

40

What are the role of  chaperones and how do they affect cancer?

Chaperones help to fold proteins correctly.

New cancer drugs target chaperones

Cancer cells have many misfolded proteins and have increased levels of chaperones

By inhibiting chaperones, the cell well have to many misfolded proteins and need to commit suicide

41

What are amyloid fibers?

increase in beta sheets leads to self-association and the formation of amyloid fibers

42

Histone Regulation

Tails of histones are modified by acetylation (by adding acetyl group the overall positive charge on lysing is removing making it more difficult to neutralize the negative charge on DNA.

HATS- histone acetyltransferases- makes euchromatin -open to transcription

HDAC-histone deacetyltransferases-makes heterochromatin- closed to transcription

*HDACs are upregualted in cancer cells to silence tumor suppressor gene, HDAC inhibitor are used as anticancer drugs

43

Describe relationship between vitamins, cofactors, apoenzymes, and holoenzymes

Vitamins- act as cofactors for enzymes

Cofactors- binds to active site of enzyme, can be bound for lifetime of the enzymes or can bin transiently like other substrate or product

Apoenzymes- enyme without its cofactor

Holoenzymes- enzyme + cofactor (able to convert substrate to product)

44

Describe chemical basis of

Thymine dimers

Deamination

Depurinaton

and what the cell does to repair these damages

Thymine dimers- heat excited pryimidines and adjacent bases form covalent dimers (nucleotide excision repair)

Deamination- removal of NH3 (coverts cytosine to uracil) (base excision repair)

Depurination- looses guanine or adenine (base excision repair)

45

What causes double stranded DNA breaks?

ionizing radiation, oxidizing agents, replication errors, certain metabolic cellular products

46

What are homologous and non-homologus end joining?

Non-homologus end joining- (most common), creates overhangs, fills in, ligates together (loss of sequence)- occurs in G1 phase, utilizing Ku protein for end recognition of double stranded breaks

Homolgous end joining- untilizes undamaged homolgous chromosome and general recombination mechanisms - no loss of sequence, more work for cell, RAD 51 protein mediates

47

What is strand directed mistmatch repair and how does it work?

1. Recognizes mis matched base

2. MutS binds specifically to a mismatched base

3. Mut L looks for nick (newly made strand) upstream and triggers degradation of the nicked strand all the way back through the mis match

4. DNA pol goes back to repair

48

Base Excision Repair

single base repair, recognizes wrong base

1. glycosylase takes out base

2. Ap endonuclease and phosphodiesterase removes sugar and phosphate

3. DNA pol adds new nucleotides, ligase seals nick

49

Nucleotide Excision Repair

- recognizes T dimers

-excision nuclease takes out problem area

-DNA pol adds new nucleotides, ligase seals nick

50

What is Benzo[a]prene ? and how does it work?

Pro-carcinogen produced by cigarette smoke

Needs oxidation to be carcinogenic

Binds covalently with guanine residues in DNA (bulky adducts, interrupts G-C base pairing and distorts double helix)

Results in G to A transisition mutation (purine to purine)

*p53 tumor suppressor gene is mutant in most cancers (espcially lung cancers)

51

How does glucose enter the cell? What is there relative affinity?

Glucose enters the cell by facilitated diffusion through GLUT transporters

GLUT 1 & 3: most cells/ hight affinity (Kd= 1 mM)

GLUT 2: liver and pancrease/ low affinity (Kd= 15-20)

GLUT 4: insulin induced/ medium affinity (Kd= 5)

SGLT: intestinal/ kidney (secondary active transport with Na+ gradient)

Note: if blood [glucose] is > Kd constant, cells will be utilizing those transporters

52

Michaelis- Menten Plots

Lineweaver-Burk Plots

For M.M.:

If line shifts to the left- it is an activator

If line shifts to the right- it is an inhibitor

If line goes from sigmoidal to hyperbolic it is allosteric activator/inhibitor

For L.B.:

(y-intercept is inverse Vmax, x-intercept is inverse Km)

Inhibitor (slope increases)

Competitive inhibition: Y intercept stays the same

Non competitive inhibition: X intercept stays thesame

Closer line is to 0 the bigger it gets

53

Hexokinase vs. glucokinase

First regulatory step in glycolysis

Hexokinase: found in most cells, low Km

Glucokinase: found in liver, high Km

Regulated by products/reactants- makes glucose 6-phophate which also inhibits it

54

What are the inhibitor and activators of phosphofructokinase-1 (PFK1)

Activators: AMP, and Fructose 2-6, bisphophate

Inhibitors: ATP, and citrate

Note** fructose 2,6 bisphophate is made from fructose 6-phosphate when there is access (PFK1's reactant)

55

What are the three regulatory steps in glycolysis?

1.hexokinase/glucokinase

2.phosphofructorkinase

3.Pyruvate kinase

56

Tryptophan operon

No trp= operon on -> makes trp

lots of trp -> binds to repressor -> makes repressor active and bind to DNA -> no trp

 

57

Lac Operon

 

Lactose present:

Lactose present inceases allactose, allactose binds to repressor and removes from operator

Glucose present: 

Glucose decreases [cAMP], cAMP no longer binds CAP(gene activator), CAP dissociates from DNA turning off operon

*In order for operon to be ON, needs to be lactose and no glucose

58

What is epigenetics?

heritable, reversible changes in genome (NO CHANGE IN SEQUENCE)

59

X inactivation in females

two XX chromosomes

one is randomly silenced, my single RNA (XIST)

all progeny will have the same X chromosome silenced

(direct inheritance of the pattern of chromosome condensation)

60

Imprinting

differential expression of a gene allele depending on parental origin

imprinting is created in parental germ cells-

if paternally  imprinted- both alleles in male germ line are methylated

61

TPP

Reactions: decarboxylase

Precursor: Thaimine

From foods: meat, legumes

Deficiency: Beri Beri (headache malaise, peripheral neurpathy, heart failure)

62

Lipoate

Reaction: acetyl transferase 

No vitamin precusor

Wide spread in diet, no know deficiencies

63

Coenzyme A

Reactions: acetyl group acceptor (acyltransferase)

Wide spread in diet

no known deficiencies

64

FAD

Rxn :Electron acceptor (oxidizes lipoate)

Precursor: Riboflavin

Found in: mushrooms, organ meats, legumes

Deficiency: cheilosis, glossitits, keratitis

 

65

NAD

Rxn: electron acceptor (oxidized FADH2)

Precursor: Niacin

Found in: fortified grains, meats

Deficiency: Pellagra 3D's

dermatits, diarrhea, dementia

66

Biotin

Rxns: carboxylase Rxns

 wide spread in diet

can be free or protein bound

regeneratable

Deficiency- raw eggs, Aviden binds to biotin 

67

Ascorbic Acid

Reactions: Hydroxylase 

Vitamin C, no precursor/ not modified by body

Deficiency- Scury

slow wound healing, irritability, apathy, anemia

 

68

PLP

Rxns: transaminases

Precursor: B6 vitamins

Found in: fortified cerals, meat, bananas, rice

Deficiency: peripheral neuropathy, siezures/ anemia in infants

Test: If siezures resolve with pyridoxal but no pryidoxine then it is a pyridoxine oxidase deficiency

If either one works then it was an antiquitin deficiency

69

Hydrophobic side chains (intertior protein structure

Alanine

Proline

Valine

Leucine

Isolucine

Tyrptophaon

Phenyalanine

Tyrosine (hydrophobic stacking with rings)

70

Uncharged and can form H bonds

Asparagine

glutamine

serine

threonine

tryosine

cysteine

71

Oxidation results in disculfide bond

cysteine

72

Charge-charge (depends on pH)

Aspartate

Glutamate

Arginine

Lysine

Histidine

73