Curriculum

17 Sections
1548 Lessons
100 Days

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U01.01 Biochemistry
This biochemistry review for USMLE Step 1 covers essential topics including metabolism, enzymology, and molecular biology.
126
U01.02 Immunology
Prepare for USMLE Step 1 Immunology with a comprehensive review covering foundational concepts, immune system mechanisms, and key disorders to solidify your understanding and boost exam readiness.
42
U01.03 Microbiology
Review essential microbiology topics for the USMLE Step 1, covering key pathogens, mechanisms of disease, and antimicrobial principles critical for mastering infectious disease concepts.
172
U01.04 General Pathology
Explore key concepts in general pathology essential for the USMLE Step 1. This review covers fundamental principles, disease mechanisms, and clinical correlations to help you excel in your medical exam.
35
U01.05 Pharmacology
Master key pharmacology concepts for the USMLE Step 1 with a focus on drug mechanisms, therapeutic uses, adverse effects, and interactions essential for high-yield exam performance.
43
U01.06 Public Health Sciences
Review essential Public Health Sciences topics for the USMLE Step 1, covering epidemiology, biostatistics, health policy, and ethics to strengthen your understanding of foundational public health principles.
53
U01.07 Cardiovascular system
Comprehensive review of essential cardiovascular system topics to help you excel in the USMLE Step 1 exam, covering key concepts from anatomy to pathology.
73
U01.08 Endocrine system
Master essential concepts of the endocrine system for USMLE Step 1, covering hormone regulation, feedback mechanisms, and key disorders to boost your exam readiness.
51
U01.09 Gastrointestinal system
Review key topics in the gastrointestinal system for the USMLE Step 1, covering essential concepts in anatomy, physiology, pathology, and pharmacology to reinforce your understanding and test readiness.
131
U01.10 Hematology and Oncology
This review covers essential Hematology and Oncology topics for the USMLE Step 1, including hematopoiesis, coagulation, anemias, leukemias, lymphomas, and neoplastic syndromes.
148
U01.11 Musculoskeletal, Skin, and Connective Tissue
Review essential topics for the USMLE Step 1 Musculoskeletal, Skin, and Connective Tissue systems, covering anatomy, physiology, pathology, and pharmacology fundamentals critical for exam success.
178
U01.12 Neurology and Special Senses
Master the foundational concepts of Neurology and Special Senses with our USMLE Step 1 review, covering essential topics like neuroanatomy, neurophysiology, and sensory pathways.
143
U01.13 Psychiatry
Psychiatry for the USMLE Step 1 focuses on understanding the pathophysiology, diagnosis, and treatment of psychiatric disorders, with an emphasis on key concepts like neurotransmitter imbalances, mental health disorders, and pharmacology.
83
U01.14 Renal System
The Renal System review for USMLE Step 1 covers key concepts including renal physiology, nephron function, acid-base balance, electrolyte regulation, and renal pathology, crucial for understanding both normal and abnormal kidney functions.
81
U01.15 Reproductive System
The USMLE Step 1 Reproductive System review covers key concepts in human reproduction, including anatomy, physiology, endocrinology, and common pathologies affecting both male and female reproductive health.
124
U01.16 Respiratory System
The Respiratory System review for the USMLE Step 1 covers key concepts in anatomy, physiology, pathophysiology, and pharmacology essential for understanding respiratory diseases and treatments.
61
U01.17 Rapid Review
he USMLE Step 1 Rapid Review covers essential topics across multiple disciplines, providing a concise, high-yield overview to reinforce key concepts and optimize your exam preparation.
5

Cell envelope

The bacterial cell envelope consists of several layers that provide structure, protection, and interaction with the external environment. It plays a critical role in determining bacterial classification, particularly in distinguishing between Gram-positive and Gram-negative bacteria.

Components of the Bacterial Cell Envelope

1. Gram-positive vs. Gram-negative bacteria

Bacteria are categorized based on the structure of their cell envelope, which is revealed by the Gram staining method.

Component	Gram-Positive Bacteria	Gram-Negative Bacteria
Cell Wall Thickness	Thick (multilayered peptidoglycan)	Thin (single layer peptidoglycan)
Outer Membrane	Absent	Present
Teichoic and Lipoteichoic Acids	Present	Absent
Periplasmic Space	Absent	Present (contains β-lactamase)
Endotoxin (LPS)	Absent	Present (lipopolysaccharide in outer membrane)

Gram-positive vs. Gram-negative bacteria

2. Common Components in Both Gram-Positive and Gram-Negative Bacteria

Peptidoglycan

A mesh-like polymer that provides structural integrity to the bacterial cell wall.
Thicker in Gram-positive bacteria and thinner in Gram-negative bacteria.

Cytoplasmic Membrane

A phospholipid bilayer that functions as a selective barrier for the transport of molecules.
Present in both types of bacteria.

Capsule

A polysaccharide layer is found outside the cell wall that helps protect bacteria from phagocytosis and desiccation.
Found in both Gram-positive and Gram-negative bacteria, though more common in Gram-negative species.

Flagellum

A tail-like structure is used for motility.
Found in both Gram-positive and Gram-negative bacteria but with differences in structure.

Pili (Fimbriae)

Hair-like appendages on the surface of both Gram-positive and Gram-negative bacteria.
Used for attachment to surfaces or other cells, facilitating processes like conjugation.

3. Unique to Gram-Negative Bacteria

Porins

Protein channels located in the outer membrane that allow the passage of small molecules.
Absent in Gram-positive bacteria.

Lipopolysaccharide (LPS)

Also known as endotoxin, LPS is present in the outer membrane of Gram-negative bacteria.
It is a potent immune activator, leading to inflammatory responses.

Periplasmic Space

The space between the inner and outer membranes contains enzymes like β-lactamase that degrade antibiotics.

4. Unique to Gram-Positive Bacteria

Lipoteichoic Acid

Anchored in the cytoplasmic membrane and extends through the peptidoglycan layer.
Helps in maintaining cell wall structure and plays a role in cell division.

Points to Remember

Gram-positive bacteria have a thick peptidoglycan layer and no outer membrane.
Gram-negative bacteria have a thin peptidoglycan layer but possess an outer membrane containing LPS.
The periplasmic space in Gram-negative bacteria contains enzymes like β-lactamase, which contribute to antibiotic resistance.
Both Gram-positive and Gram-negative bacteria can have capsules and pili for protection and adhesion, respectively.
Lipoteichoic acid is unique to Gram-positive bacteria, while LPS and porins are unique to Gram-negative bacteria.

Bibliography

Madigan MT, Martinko JM, Bender KS, et al. Brock Biology of Microorganisms. 14th ed. Pearson; 2014.
Willey JM, Sherwood LM, Woolverton CJ. Prescott’s Microbiology. 9th ed. McGraw-Hill Education; 2014.
Murray PR, Rosenthal KS, Pfaller MA. Medical Microbiology. 8th ed. Elsevier Health Sciences; 2015.

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USMLE Step 1 Review Series