Notes, summaries, assignments, exams, and problems for Biology

Citric Acid Cycle

The citric acid cycle is a series of eight reactions in which an acetyl group is decarboxylated and oxidized, generating:

• 3 molecules of NADH
• 1 molecule of FADH2
• 2 molecules of CO2
• 1 molecule of ATP (or GTP)

For each molecule of glucose entering glycolysis, two molecules of pyruvate are produced. Pyruvate is then converted to two molecules of acetyl CoA, which can enter this cycle.

Oxygen is used indirectly in cellular respiration. Glycolysis breaks down a glucose molecule, generating two molecules of pyruvate. Pyruvate moves into the mitochondrial matrix. Inside the matrix, pyruvate is converted to acetyl CoA, which then enters the citric acid cycle.

Key steps in the cycle include:

• Acetyl CoA reacts with a molecule of oxaloacetate

4 Key Differences Between Living and Inert Matter

Living systems (LS) are highly organized. An animal or plant is a complex organism constituted of different parts, each specialized in a different role. Living systems obtain nutrients from the external environment, which are then used for growth and conservation. Living systems individually reproduce. Through this function, they are capable of generating new, similar beings. In simple terms, single-celled living systems are constituted of one type of molecule with specific characteristics, such as glucides, lipids, and vitamins.

Schematic Organization of Living Systems

Levels:

Elementary Particles > Atoms > Simple Molecules > Complex Molecules > Cellular Organelles > Cells (Single-... Continue reading "Living vs. Inert: Characteristics, Organization, and Biomolecules" »

Common Diseases: An Overview

Antibiotics

Antibiotics: Penicillin, Aminoglycosides, Cephalosporins, Chloramphenicol.

Bacterial Resistance

Unnecessary use of antibiotics favors the development of bacterial resistance. Antibiotics will not kill bacteria caused by viruses. The appearance of antibiotic resistance is not just due to clinical administration to people but also the massive use of antibiotics in veterinary medicine and breeding. Bacterial resistance emerges because all organisms have slight genetic differences.

AIDS

AIDS is caused by a lethal virus with RNA. It destroys the immune system, which is supposed to protect the body. Transmission occurs through bodily fluids, such as through sexual contact or sharing syringes or blades. It is not... Continue reading "Understanding Common Diseases: Prevention and Treatment" »

Primary Structure

Primary Structure: Amino acid sequence, description of all main covalent disulfide bonds and peptide bonds.

• Superfamily: Homology 30%.
• Families: Greater than 50% homology and usually the same function.

Enzymes that break peptide bonds:

• Trypsin
• Chymotrypsin
• Pepsin
• Papain

Predictions from primary structure:

• Homology
• Hydrophobicity
• Secondary structure
• HPLC chromatographic retention
• Accessible and hidden residues
• Mutability

Secondary Structure

Secondary Structure: Folding of the polypeptide chain that occurs due to the formation of hydrogen bonds between the atoms forming the peptide bond.

Structures formed:

• Alpha-helix
• Beta-sheet
• Beta-turn

Examples:

• Alpha-helix: Myoglobin (globular protein), Fibrinogen (fibrous protein)
• Beta-sheet: Fibroin (fibrous

DNA and RNA Structure

A nucleoside is formed when a pentose sugar combines with a nitrogenous base (NB). Adding a phosphate group to a nucleoside creates a nucleotide. Nucleotides are linked by O-glycosidic phosphodiester bonds. DNA adopts a right-handed double helix structure, with hydrophobic NBs at the core and hydrophilic pentose and phosphate groups on the exterior. The major groove serves as the interaction site for replication, while the minor groove contributes to structural maintenance. Approximately 10 base pairs span 3.4 nm.

Ribosomal RNA (rRNA)

Ribosomes consist of two subunits: a large subunit (50S in prokaryotes, 60S in eukaryotes) and a small subunit (30S in prokaryotes, 40S in eukaryotes).

DNA Replication

DNA replication must be... Continue reading "DNA, RNA, and Replication: A Deep Dive into Molecular Biology" »

Skeletal Striated Muscle Cells

Skeletal striated muscle cells are elongated and have hundreds of peripheral nuclei. The cytoplasmic membrane (sarcolemma) encloses the cytoplasm (sarcoplasm), which is packed with:

• Myofibrils
• Sarcoplasmic reticulum
• T tubules
• Mitochondria

Myofibrils are composed of sarcomeres arranged in series. Each myofibril consists of thin (actin) and thick (myosin) myofilaments.

Sarcomere Structure

The sarcomere (from Greek sarco meaning "flesh" or "meat" and meres meaning "part") features:

• A central, dark A band (anisotropic)
• Two peripheral, light I bands (isotropic)

The sarcomere contains globular proteins such as troponin and tropomyosin. The sliding of thin filaments between thick filaments causes muscle contraction. During contraction,... Continue reading "Striated Muscle Cells: Skeletal vs. Cardiac" »

Earth's Biosphere and Ecosystems

The biosphere of the Earth is established by living organisms within a thin layer where energy comes from the sun. An ecosystem is formed by a community of living organisms that occupy a given space, the relationships established between them, and the physical environment.

Key Ecological Concepts

• Ecotone: Areas that limit ecosystems.
• Habitat: The area that presents the physicochemical conditions required for a population to properly function.

Components of an Ecosystem

Landforms are part of the ecosystem, which is part of the ecosphere. The components include:

• Biocenosis: The community of living organisms.
• Biotopo: The physical environment.

Biotopo Components

These include:

• Characteristics of the substrate: The support

Eye

Cornea

1. Anterior corneal epithelium
2. Bowman's membrane
3. Stroma
4. Descemet's membrane
5. Corneal endothelium

Choroid

1. Vascular layer (arteries and veins around conjunctiva lax with melanocytes)
2. Choriocapillaris layer (capillary network in 1 flat)
3. Bruch's membrane

Retina

1. Nerve fiber layer
2. Ganglion cell layer
3. Inner plexiform layer
4. Inner nuclear layer
5. Outer plexiform layer
6. Outer nuclear layer
7. Outer limiting membrane
8. Rod and cone layer
9. Pigment epithelium

Eyelids

(Outside to inside):

1. Skin and dermis of TCL
2. Bundles of striated muscle (orbicularis oculi muscle)
3. Thickened set at the ends (eyelid plates with meibomian glands)
4. Mucous layer (conjunctiva)

Glands: Moll (sweat), Meibomian and Zeis (sebaceous)

Inner Ear

Above the sensory epithelium of the macula are otoliths (calcium carbonate... Continue reading "Female Reproductive and Sensory Organs" »

Metabolic Regulation

Enzymes do not always act with the same degree of cellular boost to the economy. Regulation governs many metabolisms at these levels: synthesis and modification of enzyme structure, [S] and [P]. Thus, enzyme inhibition is a control mechanism of cellular metabolism. An important example is allosteric enzymes, whose speed depends not only on the interplay of [S] but also on other substances. Then, in addition to the active sites, they have other allosteric sites that activate them or act as regulatory molecules.

Types of Metabolic Regulation

• Negative Feedback (Feedback Regulation): The product inhibits the pathway.
• Positive Control: The product stimulates the start of the pathway.

Nucleic Acids

Nucleic acids are substances found... Continue reading "Metabolic Regulation and Nucleic Acids: DNA and RNA Functions" »

Transcription and mRNA Processing

Transcription occurs within the nucleus. During this process, introns are removed from the pre-mRNA, creating a mature mRNA molecule. This mature mRNA then migrates from the nucleus to the cytoplasm.

Translation Initiation and Elongation

Once in the cytoplasm, the mRNA is recognized by the ribosome. This recognition occurs via specific sequences in bacteria and the 5' cap in eukaryotes. The ribosome then initiates the translation process.

tRNA molecules act as adapters between amino acids and mRNA. Each tRNA has a region that binds to a specific amino acid and another region, the anticodon, that recognizes a triplet of nucleotides (a codon) in the mRNA.

Translation begins when the ribosome identifies the start... Continue reading "mRNA Translation: From Transcription to Protein Synthesis" »