1/6/20, 9:01:48 PM
Compare Results
New File:
Old File:
First Aid for the USMLE Step 1 2020, Thirtieth
FA 2019.pdf
versus edition-1.pdf
62 pages (293.11 MB)
62 pages (109.99 MB)
1/5/20, 12:57:57 PM
1/5/20, 12:52:18 PM
BY u/verified-idiot
To the only girl i've ever loved, to soufia.
BLUE new in FA 2020
YELLOW text of FA 2019 was edited; the note box next to the yellow highlight will show the difference between
them the old text and the new text of FA 2020
Some pages might look scary! because of note boxes and highlighting , but it is not, my recommendation for
you is to study your book and after than look for the new stuff and edits.. I DONT recommend comparing while
you are studying since it will consume your time.
Go to First Change (page 2)
file://NoURLProvided[1/6/20, 9:01:48 PM]
,HIGH-YIELD PRINCIPLES IN
Biochemistry
“Biochemistry is the study of carbon compounds that crawl.” ` Molecular 34
—Mike Adams
` Cellular 46
“We think we have found the basic mechanism by which life comes from
life.” ` Laboratory Techniques 52
—Francis H. C. Crick
` Genetics 56
“The biochemistry and biophysics are the notes required for life; they
conspire, collectively, to generate the real unit of life, the organism.” ` Nutrition 65
—Ursula Goodenough
` Metabolism 72
This high-yield material includes molecular biology, genetics, cell
biology, and principles of metabolism (especially vitamins, cofactors,
minerals, and single-enzyme-deficiency diseases). When studying
metabolic pathways, emphasize important regulatory steps and enzyme
deficiencies that result in disease, as well as reactions targeted by
pharmacologic interventions. For example, understanding the defect
in Lesch-Nyhan syndrome and its clinical consequences is higher yield
than memorizing every intermediate in the purine salvage pathway.
Do not spend time learning details of organic chemistry, mechanisms, or
physical chemistry. Detailed chemical structures are infrequently tested;
however, many structures have been included here to help students
learn reactions and the important enzymes involved. Familiarity with
the biochemical techniques that have medical relevance—such as
ELISA, immunoelectrophoresis, Southern blotting, and PCR—is
useful. Review the related biochemistry when studying pharmacology or
genetic diseases as a way to reinforce and integrate the material.
33
,34 SEC TION II BIOCHEMISTRY `B̀IOCHEMISTRY—MOLECULAR
``
BIOCHEMISTRY—MOLECULAR
Chromatin structure DNA exists in the condensed, chromatin form to
fit into the nucleus. DNA loops twice around a
histone octamer to form a nucleosome (“beads
DNA double-helix on a string”). H1 binds to the nucleosome
and to “linker DNA,” thereby stabilizing the
chromatin fiber.
H1 histone Phosphate groups give DNA a ⊝ charge. Lysine
(linker)
DNA and arginine give histones a ⊕ charge.
In mitosis, DNA condenses to form
chromosomes. DNA and histone synthesis
Nucleosome Euchromatin Supercoiled occurs during S phase.
(H2A, H2B, structure Mitochondria have their own DNA, which is
H3, H4) 2 Heterochromatin circular and does not utilize histones.
Metaphase
chromosome
Heterochromatin Condensed, appears darker on EM (labeled H HeteroChromatin = Highly Condensed.
A
in A ; Nu, nucleolus). Sterically inaccessible, Barr bodies (inactive X chromosomes) may be
E thus transcriptionally inactive. methylation, visible on the periphery of nucleus.
H acetylation.
Nu
Euchromatin Less condensed, appears lighter on EM (labeled Eu = true, “truly transcribed.”
E in A ). Transcriptionally active, sterically Euchromatin is Expressed.
accessible.
DNA methylation Changes the expression of a DNA segment DNA is methylated in imprinting.
without changing the sequence. Involved with Methylation within gene promoter (CpG islands)
aging, carcinogenesis, genomic imprinting, typically represses (silences) gene transcription.
transposable element repression, and CpG Methylation Makes DNA Mute.
inactivation of the X chromosome.
Histone methylation Usually causes reversible transcriptional Histone Methylation Mostly Makes DNA Mute.
suppression, but can also cause activation
depending on location of methyl groups.
Histone acetylation Removal of histone’s ⊕ charge relaxed DNA Histone Acetylation makes DNA Active.
coiling transcription.
Histone deacetylation Removal of acetyl groups tightened DNA
coiling transcription.
, BIOCHEMISTRY `B̀IOCHEMISTRY—MOLECULAR SEC TION II 35
Nucleotides NucleoSide = base + (deoxy)ribose (Sugar).
NucleoTide = base + (deoxy)ribose + phosphaTe; 5′ end of incoming nucleotide bears the
linked by 3′-5′ phosphodiester bond. triphosphate (energy source for the bond).
Triphosphate bond is target of 3′ hydroxyl
attack.
PURines (A,G)—2 rings. PURe As Gold.
PYrimidines (C,U,T)—1 ring. CUT the PY (pie).
Thymine has a methyl.
Deamination reactions: C-G bond (3 H bonds) stronger than A-T bond
Cytosine uracil (2 H bonds). C-G content melting
Adenine hypoxanthine temperature of DNA. “C-G bonds are like
Guanine xanthine Crazy Glue.”
5-methylcytosine thymine
Amino acids necessary for purine synthesis (cats
Uracil found in RNA; thymine in DNA. purr until they GAG):
Methylation of uracil makes thymine. Glycine
Aspartate
Purine (A, G) Pyrimidine (C, U, T)
Glutamine
CO2
Carbamoyl Aspartate
Aspartate Glycine phosphate
C N C
N C N C
C N10–Formyl-
C C tetrahydrofolate C C
N N N
N10–Formyl-
Glutamine
tetrahydrofolate
Compare Results
New File:
Old File:
First Aid for the USMLE Step 1 2020, Thirtieth
FA 2019.pdf
versus edition-1.pdf
62 pages (293.11 MB)
62 pages (109.99 MB)
1/5/20, 12:57:57 PM
1/5/20, 12:52:18 PM
BY u/verified-idiot
To the only girl i've ever loved, to soufia.
BLUE new in FA 2020
YELLOW text of FA 2019 was edited; the note box next to the yellow highlight will show the difference between
them the old text and the new text of FA 2020
Some pages might look scary! because of note boxes and highlighting , but it is not, my recommendation for
you is to study your book and after than look for the new stuff and edits.. I DONT recommend comparing while
you are studying since it will consume your time.
Go to First Change (page 2)
file://NoURLProvided[1/6/20, 9:01:48 PM]
,HIGH-YIELD PRINCIPLES IN
Biochemistry
“Biochemistry is the study of carbon compounds that crawl.” ` Molecular 34
—Mike Adams
` Cellular 46
“We think we have found the basic mechanism by which life comes from
life.” ` Laboratory Techniques 52
—Francis H. C. Crick
` Genetics 56
“The biochemistry and biophysics are the notes required for life; they
conspire, collectively, to generate the real unit of life, the organism.” ` Nutrition 65
—Ursula Goodenough
` Metabolism 72
This high-yield material includes molecular biology, genetics, cell
biology, and principles of metabolism (especially vitamins, cofactors,
minerals, and single-enzyme-deficiency diseases). When studying
metabolic pathways, emphasize important regulatory steps and enzyme
deficiencies that result in disease, as well as reactions targeted by
pharmacologic interventions. For example, understanding the defect
in Lesch-Nyhan syndrome and its clinical consequences is higher yield
than memorizing every intermediate in the purine salvage pathway.
Do not spend time learning details of organic chemistry, mechanisms, or
physical chemistry. Detailed chemical structures are infrequently tested;
however, many structures have been included here to help students
learn reactions and the important enzymes involved. Familiarity with
the biochemical techniques that have medical relevance—such as
ELISA, immunoelectrophoresis, Southern blotting, and PCR—is
useful. Review the related biochemistry when studying pharmacology or
genetic diseases as a way to reinforce and integrate the material.
33
,34 SEC TION II BIOCHEMISTRY `B̀IOCHEMISTRY—MOLECULAR
``
BIOCHEMISTRY—MOLECULAR
Chromatin structure DNA exists in the condensed, chromatin form to
fit into the nucleus. DNA loops twice around a
histone octamer to form a nucleosome (“beads
DNA double-helix on a string”). H1 binds to the nucleosome
and to “linker DNA,” thereby stabilizing the
chromatin fiber.
H1 histone Phosphate groups give DNA a ⊝ charge. Lysine
(linker)
DNA and arginine give histones a ⊕ charge.
In mitosis, DNA condenses to form
chromosomes. DNA and histone synthesis
Nucleosome Euchromatin Supercoiled occurs during S phase.
(H2A, H2B, structure Mitochondria have their own DNA, which is
H3, H4) 2 Heterochromatin circular and does not utilize histones.
Metaphase
chromosome
Heterochromatin Condensed, appears darker on EM (labeled H HeteroChromatin = Highly Condensed.
A
in A ; Nu, nucleolus). Sterically inaccessible, Barr bodies (inactive X chromosomes) may be
E thus transcriptionally inactive. methylation, visible on the periphery of nucleus.
H acetylation.
Nu
Euchromatin Less condensed, appears lighter on EM (labeled Eu = true, “truly transcribed.”
E in A ). Transcriptionally active, sterically Euchromatin is Expressed.
accessible.
DNA methylation Changes the expression of a DNA segment DNA is methylated in imprinting.
without changing the sequence. Involved with Methylation within gene promoter (CpG islands)
aging, carcinogenesis, genomic imprinting, typically represses (silences) gene transcription.
transposable element repression, and CpG Methylation Makes DNA Mute.
inactivation of the X chromosome.
Histone methylation Usually causes reversible transcriptional Histone Methylation Mostly Makes DNA Mute.
suppression, but can also cause activation
depending on location of methyl groups.
Histone acetylation Removal of histone’s ⊕ charge relaxed DNA Histone Acetylation makes DNA Active.
coiling transcription.
Histone deacetylation Removal of acetyl groups tightened DNA
coiling transcription.
, BIOCHEMISTRY `B̀IOCHEMISTRY—MOLECULAR SEC TION II 35
Nucleotides NucleoSide = base + (deoxy)ribose (Sugar).
NucleoTide = base + (deoxy)ribose + phosphaTe; 5′ end of incoming nucleotide bears the
linked by 3′-5′ phosphodiester bond. triphosphate (energy source for the bond).
Triphosphate bond is target of 3′ hydroxyl
attack.
PURines (A,G)—2 rings. PURe As Gold.
PYrimidines (C,U,T)—1 ring. CUT the PY (pie).
Thymine has a methyl.
Deamination reactions: C-G bond (3 H bonds) stronger than A-T bond
Cytosine uracil (2 H bonds). C-G content melting
Adenine hypoxanthine temperature of DNA. “C-G bonds are like
Guanine xanthine Crazy Glue.”
5-methylcytosine thymine
Amino acids necessary for purine synthesis (cats
Uracil found in RNA; thymine in DNA. purr until they GAG):
Methylation of uracil makes thymine. Glycine
Aspartate
Purine (A, G) Pyrimidine (C, U, T)
Glutamine
CO2
Carbamoyl Aspartate
Aspartate Glycine phosphate
C N C
N C N C
C N10–Formyl-
C C tetrahydrofolate C C
N N N
N10–Formyl-
Glutamine
tetrahydrofolate
