Biology Chapter Concepts

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Questions and Answers

Within the human genome, how many nucleolar organizer regions (NORs) are present?

10 (correct)

Which process does not occur within the nucleus?

mRNA transcription

DNA replication

Ribosome assembly

Protein translation (correct)

The endoplasmic reticulum's primary function does NOT include

Direct assembly of proteins (correct)

Facilitating intracellular transport routes

Increasing the cell's internal surface area

Creating distinct cytoplasmic compartments

What is a key distinction between the smooth and rough endoplasmic reticulum?

The presence of ribosomes on the rough ER Signup and view all the answers

What are ribosomes primarily made of?

rRNA and proteins Signup and view all the answers

Which of the following best describes the primary characteristic that allows carbon to form a wide variety of biological molecules?

Carbon's ability to form strong covalent bonds, particularly with other carbon atoms. Signup and view all the answers

What is the maximum number of carbon atoms typically found in the small organic molecules of a cell?

30 Signup and view all the answers

Which of the following lists the four major families of small organic molecules found within cells?

Saccharides, fatty acids, amino acids, and nucleotides Signup and view all the answers

How does the length of the carbon chain in a carbohydrate affect its solubility in water?

The longer the carbon chain, the less soluble the carbohydrate is in water. Signup and view all the answers

Which of the following is a primary function of carbohydrates in living organisms?

To store and produce energy, along with structural support. Signup and view all the answers

What structural characteristic distinguishes saturated from unsaturated fatty acids?

The presence of one or more double bonds. Signup and view all the answers

What is a defining characteristic of lipids, related to their interaction with water?

They are insoluble in water because of their limited capacity to polarize. Signup and view all the answers

Which of the following describes the monomer of a polysaccharide?

A monosaccharide Signup and view all the answers

Which of these components are not a part of sphingomyelin?

Sugar molecule Signup and view all the answers

What distinguishes cerebrosides from more complex gangliosides?

Cerebrosides contain one sugar residue, while gangliosides may contain up to seven. Signup and view all the answers

What is the core structural characteristic of sterols that distinguishes them from other lipids?

They contain a cyclic compound with a branched side chain. Signup and view all the answers

How does the presence of unsaturated bonds in fatty acid residues affect their structure within membrane lipids?

It causes the fatty acid to take up more space. Signup and view all the answers

Which of these is an accurate description of amphiphilic molecules?

They simultaneously exhibit a hydrophilic and a hydrophobic region. Signup and view all the answers

What is the fundamental structural arrangement of the cell membrane?

A phospholipid bilayer. Signup and view all the answers

In membrane lipids, what is a common range for the length of fatty acid residues in terms of carbon atoms?

16 to 18 carbon atoms Signup and view all the answers

In terms of charge, how can the hydrophilic part of a membrane phospholipid behave?

Being electrically charged or having polar character of an electric dipole. Signup and view all the answers

What structural feature prevents membrane lipids from escaping the bilayer?

The aqueous environment both inside and outside of the cell Signup and view all the answers

Which statement best describes the arrangement of integral membrane proteins within the lipid bilayer?

They interact with the membrane's lipid hydrocarbon tails via hydrophobic amino acids Signup and view all the answers

A polytopic membrane protein is characterized by which of the following structural features?

It spans the plasma membrane multiple times. Signup and view all the answers

Which of these protein categories are not penetrating the plasma membrane?

Transmembrane proteins Signup and view all the answers

Peripheral membrane proteins are able to associate with the cell membrane through:

Electrostatic/ionic and hydrogen bonds Signup and view all the answers

Cell surface proteins are distinguished from other proteins by their:

Attachment to the cell membrane through an anchor motif. Signup and view all the answers

Which of the following is NOT a primary function of membrane proteins?

To form a barrier preventing the movement of molecules across the membrane Signup and view all the answers

What aspect of integral membrane proteins allows passage of some polar molecules and water?

The hydrophilic parts facing internally Signup and view all the answers

What is the primary trigger for ribophagy?

Demand for nitrogen-containing building blocks Signup and view all the answers

How does proteaphagy primarily occur?

Through binding of specific receptors to autophagosome proteins Signup and view all the answers

What defines homeostasis in an organism?

The maintenance of a relatively stable internal environment amidst external changes. Signup and view all the answers

What is a characteristic of the dynamic steady state of homeostasis?

A state where concentrations of substances differ between ECF and ICF but remain relatively stable Signup and view all the answers

What role does the extracellular fluid (ECF) play in maintaining homeostasis?

It acts as an interface between the external environment and cells. Signup and view all the answers

Why is intercellular communication crucial for multicellular organisms?

To coordinate activities among cells, tissues, and the whole organism. Signup and view all the answers

Besides cell survival, what other function relies on intercellular communication?

Cell differentiation Signup and view all the answers

When homeostasis is disrupted, and compensation is unsuccessful, what is the most likely outcome?

The organism develops a disease state. Signup and view all the answers

What is the primary distinction between neurotransmitters and neurohormones in terms of their action?

Neurotransmitters act locally across the synaptic cleft, while neurohormones have a broader effect after diffusing into the bloodstream. Signup and view all the answers

If a signaling molecule is found to induce different responses in a variety of target cells, what aspect of the cell is primarily responsible for this?

The functional specialization of the cell and the types of receptors it expresses. Signup and view all the answers

A ligand that partially activates a cell surface receptor can be described as:

A modulator Signup and view all the answers

Which of the following best describes how cell-surface receptors initiate a response within a cell after binding to a ligand?

They activate intracellular signaling molecules, which will trigger a final cellular response. Signup and view all the answers

A signaling molecule that is small and hydrophobic is most likely to interact with which type of receptor?

Intracellular receptor Signup and view all the answers

What is the principal difference between Type I and Type II nuclear receptors?

Type I receptors bind ligands in the cytoplasm, while Type II receptors bind ligands in the nucleus. Signup and view all the answers

A drug that blocks the action of a neurotransmitter by binding to its receptor is best described as a(n):

Antagonist Signup and view all the answers

Which of the following does not interact directly with a cell surface receptor?

Intracellular receptor Signup and view all the answers

Study Notes

Cell Composition and Structure

The lecturer is Dr. Michelle Kuzma, adapted from Dr. Danuta Mielżyńska-Švach
The study of cells encompasses several related fields: cytology, cytochemistry, cytopathology, cytophysiology, and cytogenetics.
A cell is the smallest living structural and functional unit that comprises all organisms.
All cells are formed by the division of other cells (cell division).
Cells contain genetic information that is passed on to daughter cells during cell division.
All cells are made up of the same chemical compounds.
All metabolic processes necessary for life occur in cells.

Types of Cells

Cells are categorized into prokaryotic and eukaryotic.
Prokaryotic cells lack a nucleus and membrane-bound organelles, but do have a nucleoid containing DNA, ribosomes, cytoplasm, a capsule (mucus), cell wall, plasma membrane and flagella (pili and fimbriae)
Eukaryotic cells contain a nucleus and membrane-bound organelles (mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes.
Prokaryotes include Bacteria and Archaea.
Eukaryotes include protists, fungi, plants, and animals.

Cell Components

All organisms are composed of two types of chemicals: inorganic and organic.
Inorganic compounds mainly constitute the inanimate part of nature; chemical elements (macroelements, microelements, trace elements, and ultratrace elements) and water are examples.
Organic compounds occur almost exclusively in living organisms or their remains and composed of carbon atoms bonded to other elements (including hydrogen and oxygen, as well as nitrogen, sulfur and phosphorus).

Inorganic Components

Chemical elements: macroelements (e.g., carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur, potassium, sodium, magnesium), microelements (Iron, Silicon, Copper, Manganese, Fluorine, Iodine, Boron, Molybdenum, Zinc), ultratrace elements (radium, silver, gold),
Water (~70%)

Chemical Elements (cont.)

Macroelements:
- Carbon (C)
- Hydrogen (H)
- Oxygen (O)
- Nitrogen (N)
- Phosphorus (P)
- Sulphur (S)
- Potassium (K)
- Sodium (Na)
- Magnesium (Mg)
Microelements:
- Iron (Fe)
- Silicon (Si)
- Copper (Cu)
- Manganese (Mn)
- Fluorine (F)
- lodine (I)
- Boron (B)
- Molybdenum (MI)
- Zinc (Zn)
Ultraelements; radium (Ra), silver (Ag) and gold (Au)

Water

The main component of every organism (70-80% of a living cell).
Essential for proper functioning of the body
Solvent for many chemical compounds (solutes) and an environment for all reactions
Substrate and product of many chemical reactions
Biological functions of water are due to its chemical structure and properties

The Structure of a Water Molecule

A water molecule consists of one oxygen atom and two hydrogen atoms.
A specialized dipole-dipole force known as a hydrogen bond exists between the oxygen and hydrogen
A hydrogen bond is inherently polarized due to the difference in electronegativity between the two atoms.
The uneven distribution of charges causes the water molecule to be dipolar.
The attraction of hydrogen atoms (2+) by oxygen atoms (2-) causes water molecules to combine into larger groups (association).

The Structure of the Carbon Atom

The nucleus of a carbon atom contains 6 protons (red) and 6 neutrons (blue).
The carbon atom has two electron shells: I (K shell)—contains 2 electrons, II (L shell)—contains 4 electrons.
A carbon atom contains four valence electrons and four vacancies for electrons from other elements.
Thus, carbon atoms can join to form chains, branched structures, and rings,
Organic compounds consist of carbon atoms bonded to at least one other element.

Organic Components

Cells contain four major families of small organic molecules (containing carbon and hydrogen): carbohydrates, fatty acids, amino acids, and nucleotides.
The small organic molecules of the cell are carbon compounds that contain up to 30 or so carbon atoms.
They are usually found free in solution in the cytosol.
Monomer subunits construct the cell's macromolecules (polymers).

Carbohydrates

Carbohydrates consist of saccharides which mainly contain carbon, hydrogen, and oxygen.
The types include: monosaccharides (e.g., glucose, fructose), disaccharides (e.g., sucrose, lactose, maltose), oligosaccharides (e.g., raffinose), and polysaccharides (e.g., cellulose, starch).
The longer the carbon chain, the less soluble the carbohydrate in water.

Carbohydrate Function

Energy storage/production:
- glycogen (animals)
- starch (plants)
Structure:
- cellulose (plant cell walls)
- chitin (fungal cell walls)
- ribose and deoxyribose sugars of DNA and RNA
Modifiers of proteins
Transport:
- glucose (animals and humans)
- sucrose (plants)

Fatty Acids

Fatty acids usually contain an even number of carbon atoms (14 to 24).
Fatty acids have a carboxyl group (acid) connected to a hydrocarbon chain (fat).
The shorter the chain, the more fluid the fatty acid.
Saturated fatty acids only have single bonds.
Unsaturated fatty acids have one or more double bonds.

Lipids

Lipids are esters of fatty acids bonded to alcohols.
Examples include glycerol, sphingosine, and higher monohydric alcohols.
Insoluble in water due to their low ability to polarize under the influence of water.
Types of lipids include: simple lipids (e.g., fats and oils (triglycerides), waxes), complex lipids (e.g., phosphoric acid - phospholipids, carbohydrate - glycolipids), and steroids (e.g., cholesterol).

Lipid Functions

Structural: building blocks of biological membranes (e.g., phospholipid bilayer, rigidity of plasma membrane).
Energy storage:
- in animals - stored as subcutaneous tissue, mainly in hibernators.
- in plants - in seeds (e.g., sunflower, soybean and rapeseed), fruits, and roots.
Signaling: steroid hormones, vitamins A and D.
Protection:
- eye balls, kidneys, other abdominal organs from mechanical injuries.
- leaves and fruits of many plants from excessive water loss, in wax coverings.
- marine mammals from low temperatures

Cell Structure: Cytoplasm

The cytoplasm is a colloidal solution (a solution in which the particles of dissolved substance are too small to settle under the influence of gravity, too large to dissolve in water and form a proper solution).
The cytoplasm has two phases:
- Dispersive - water (90% of the volume of cytoplasm)
- Dispersed - substances suspended in water (approx 9% organic compounds, and approx. 1% mineral compounds).
Functions of cytoplasm:
- fill the cell and give it shape,
- environment for cell organelles,
- site of metabolic reactions
- movement and transport of substances.
- Cytoplasm is both ductile and viscous (high in protein content), occurs in two states (sol and gel).
- Movements include rotational, circulatory, pulsating, and fountaining.

Cell Structure: Cytoskeleton

All cells have to rearrange internal components for growth, division, and adaptation.
This depends on a system of filaments called the cytoskeleton.
The three protein filament families are intermediate filaments (diameter 8–10 nm), microtubules (diameter ~25 nm), and actin filaments (diameter ~7 nm).

Cell Organelles (Eukaryotic, Animal)

A eukaryotic cell consists of numerous organelles responsible for specific functions.
These include: cytoplasm, cytoskeleton, nucleus, endoplasmic reticulum, mitochondria, Golgi apparatus, lysosomes, and peroxisomes, and plasma membrane

Cell Structure: Organelles

Membrane-bound organelles:
- Double membrane-bound: nucleus (contains genetic information), mitochondria (site of cellular respiration), chloroplasts (plant cells)
- Single membrane-bound: Golgi apparatus (modifies proteins, secretes various substances), lysosomes (contain digestive enzymes), peroxisomes (vesicles containing various compounds to breakdown peroxides), endoplasmic reticulum (network of channels that are involved in protein production and transport and lipid synthesis), vacuoles (animal cells sequester waste products, plant cells are the "garbage bins and warehouses" of the cell and sustain water balance),
Non-membrane bound organelles:
- cell wall (outer covering of some non-animal cells)
- cytoskeleton (provides cell structure)
- ribosomes (location of protein synthesis)
- centrosome (contains centrioles and microtubules important in cell division)
- centriole (cylindrical organelle involved in spindle fiber creation during cell division)

Nucleus

Amount in a human cell: monokaryocytes, bikaryocytes, polykaryocytes; zero: erythrocytes and cells of the stratum corneum of the epidermis.
Size and shape: depends on the type of cell, age and functional state (spherical, ellipsoidal, fragmented).
~10% of the cell volume of mammalian cells.
Position: in the middle of the cell or along the cell membrane
States of the nucleus: interphase (between/preparation of cell division), mitotic (during cell division), metabolic (present in cells in the resting stage; directs metabolic processes, maintenance functions).
Structures during interphase: nuclear envelope (membrane), nuclear matrix (nucleoplasm) , nucleolus, condensed chromatin (heterochromatin), dispersed chromatin (euchromatin).

Nucleolus

The nucleolus is usually unseparated from the nucleoplasm (no membrane).
It consists of fragments of five chromosomes, containing DNA responsible for the synthesis of ribosomal RNA (rRNA) and ribosomal subunits (nucleolar organizers).
In humans, there are 10 nucleolar organizers located on chromosome pairs 13, 14, 15, 21, and 22.

Nucleus Functions

site of DNA synthesis - replication of genetic information before nuclear division
site of synthesis of RNA from DNA (transcription)
site of formation of ribosomes - the structures responsible for protein synthesis (translation)

Endoplasmic Reticulum

The endoplasmic reticulum is a system of single-layer membranes that form a network of cisternae, channels and vesicles.
It ensures: enlargement of the internal surface area of the cell, division of the cytoplasm into compartments, and determines the route of transport of organelles, substrates, and products.
Types: Smooth (agranular) endoplasmic reticulum - lacks ribosomes and is involved in lipid and steroid synthesis, removal of toxic substances and internal transport, and Rough (granular), endoplasmic reticulum - contains ribosomes for protein synthesis, modification, quality control that connects the outer nuclear membrane to cell and organelle membranes

Ribosomes

Ribosomes are made up of ribosomal RNA (rRNA) and proteins.
Types of ribosomes:
- free ribosomes- located in cytoplasm to produce proteins that function in cytosol
- ribosomes attached to ER to produce proteins that undergo post-translational modification and are exported.
- ribosomes in mitochondria and chloroplasts (smaller and similar to bacteria)

Mitochondria

Number of mitochondria in a single cell depends on the organism, cell type, and energy requirements
Vary in size (2 to 8 µm)
They can change shape and size (filamentous, granular, branched)
New mitochondria are created by division of existing ones
Number in various cells:
- epidermal cells: 2 to 6
- sperm cells: 20 to 50
- liver cells: 1,000 to 2,500
- skeletal muscle fibers: up to 1,600
- skin cells: ~2,000
- nerve cells: 10,000
- ova: >100,000

Mitochondrial Structure

two-layer membrane
the outer membrane smooth allowing passive transport of substances
the inner membrane allows only selected molecules to pass, by facilitated diffusion
intermembrane space and cristae (folded inner membrane).
contains mitochondrial DNA (mtDNA), ribosomes (70S), and enzymes necessary for ATP production.
mtDNA is found as multiple molecules (4-10) of ellipsoidal nucleoids.

Mitochondrial Functions

aerobic respiration (Krebs cycle and electron transport chain).
production of ATP (adenosine-5'-triphosphate) - a carrier of chemical energy used in cell metabolism.

Golgi Apparatus

Highly flattened, arched cisternae (3–20), separating vesicles.
Stages: cis cisternae (beginning, towards nucleus/ER), medial cisternae, trans cisternae (end, towards cell membrane).
Functions:
- post-translational modification of proteins and lipids for export
- linking carbohydrates to proteins, fats, and nucleosides
- sulfation of proteins and proteoglycans
- recycling of the cell membrane after endocytosis,
receives components from the perinuclear endoplasmic reticulum, the cell membrane and endosome.

Lysosomes

Different shapes and sizes depending on cell type.
Macrophages - several microns
Hepatocytes and neurons - 0.5–1 µm.
Usually spherical or oval vesicles surrounded by a single membrane.
Number and location may differ even within the same tissue.
In hepatocytes and fibroblasts, lysosomes occupy ~0.5% of cytoplasmic volume; up to 2.5% in macrophages
Types:
- Primary - Formed in the rER
- Secondary - Formed after fusion (with endosomes or autophagosomes).
40 Hydrolytic enzymes (acid hydrolases) catalyze intracellular digestion reactions within acidic environments (pH 5).
A low pH environment is created by the transmembrane H+ ATPase / proton pump
The lysosome membrane is resistant to acid hydrolases and contains a range of unique proteins.

Peroxisomes

Oval or spherical organelles surrounded by a single membrane.
Diameter between 0.2–1.8 µm
Number, morphology and physiological role depends on the cell type, tissue, stage of development, and cellular stress
Most abundant in liver, kidney and nervous tissue.
The granular matrix of peroxisomes may contain a crystalline core called the nucleoid
Peroxisomes degrade toxic compounds (e.g. ethanol) and lipids. They catalyse B-oxidation reactions and produce hydrogen peroxide (H₂O₂)
Functions:
- Decomposition/reduction of toxic chemical compounds (detoxification)
- β-oxidation reactions of fatty acids
- α-oxidation of branched fatty acids
- cholesterol and bile acid syntheses. (independent of the endoplasmic reticulum)
- plasmalogen synthesis.
Hydrogen peroxide (H₂O₂) by-product breakdown by catalase.
Formed by two mechanisms: de novo from preperoxisomes or from the division of pre-existing peroxisomes

Centrioles

Centrosome (diplosome): located near the nucleus and Golgi apparatus and consists of two centrioles
Centrioles are composed of microtubules and appear as cylinders.
During cell division, the centrosome duplicates itself and the two centrosomes move to opposite poles of the cell.

Plant Cells

Compared to an animal cell, plant cells contain additional components: living (plasmic) components: plastids dead (nonplasmic) components: cell wall, vacuole

Plastids

Types: etioplasts, proplastids, chloroplasts, chromoplasts, amyloplasts, elaioplasts, proteinoplasts.
Function is related to storage.
Chloroplasts contain chlorophyll (permits photosynthesis), chromoplasts contain xanthophyll and carotenes, leucoplasts lack pigments and serve as storage sites for starch (amyloplasts), proteins (proteinoplasts), or fats (lipidoplasts)

Cell Wall (Plant cells)

Plant eukaryotic organisms have a multilayered cell wall made of cellulose or chitin.
Types:
- Primary (cellulose and pectin)
- Secondary (cellulose and lignin)
Functions:
- gives shape and rigidity to the cell
- limits cell growth
- protects against injuries, bacterial, fungal and viral infections, and excessive evaporation

Plant Vacuole

The vacuole is surrounded by a single membrane called tonoplast.
Cell sap components:
- water (90%)
- ions (potassium, sodium, calcium, magnesium, zinc, sulfate, chloride)
- proteins (aleurone grains and amino acids),
- sugars (glucose, fructose, sucrose),
- organic acids.
Functions:
- maintain constant cell firmness (turgor pressure),
- store reserve materials,
- gather unnecessary metabolic products.

Cell Metabolism

Metabolism encompasses all biochemical reactions in living cells.
It involves the circulation of matter, energy, and information.
These activities allow stimulus reception, growth, movement, and reproduction.
Two directions of metabolic changes: anabolism and catabolism.

Anabolism

Synthesis of complex organic compounds from simple compounds.
Requires energy input.
More energy is stored in the products than the substrates.

Catabolism

Breakdown of complex organic compounds into simple compounds.
Contains less energy in the products than the substrates.
Energy released is stored in bonds of energy carriers (e.g., ATP).

Cellular Respiration

The breakdown of organic compounds into inorganic compounds for energy.
Involves Glycolysis (in cytoplasm), where glucose is broken down into pyruvic acid (in the cytoplasm, no net production of ATP).
In Mitochondria, Pyruvic acid and intermediates are oxidized into end products (e.g., water, carbon dioxide).

Intracellular Respiration

Glycolysis in cytoplasm; Krebs cycle and electron transport in the mitochondria.

Endosymbiotic Theory

Explains the origin of mitochondria and chloroplasts in eukaryotic cells.
Mitochondria and chloroplasts:
- have their own circular DNA,
- have a similar structure and size to bacterial DNA
- are formed by division of pre-existing organelles, not de novo.
Mitochondria and chloroplast ribosomes are similar to bacterial ribosomes.

Cell Signaling

Coordination between cells involves the transmission of signals, which can be two basic types: electrical (related to changes in membrane potential) and chemical (chemical compounds secreted by cells into the extracellular space).
Cells responding to signals are called target cells.
Methods of communication depends on signal distance.
- Local: juxtacrine (contact-dependent), paracrine, autocrine
- Distant: endocrine (hormonal) and neuronal (synaptic).

Hormones

Signaling molecules:
- Examples of signaling molecules include Epinephrine (adrenaline), Cortisol, Estradiol, Insulin, Testosterone, Thyroid hormone (thyroxine), Acetylcholine, Y-Aminobutyric acid (GABA)

Intercellular Communication Principles

Only cells with receptors for signaling molecules respond (selective response).
The response of a cell depends on functional specialization and receptor types, not signaling molecule itself.
One signaling molecule can induce multiple changes in different target cells.
One signaling molecule can cause several actions in a given target cell.

Ligands

Ligands (extracellular signaling molecules) deliver information to a target cell.

Intracellular Receptors

Located in the cytoplasm or nucleus (transcription factors).
Ligands are small hydrophobic molecules (e.g., steroid hormones, thyroid hormones, vitamin D, retinoic acid) that diffuse through the cell membrane.
In their active state, they regulate gene expression, typically moving into the nucleus when ligand-bound

Types of Receptors

Intracellular: cytoplasmic receptors, nuclear receptors
Cell-surface Receptors: ion channel-linked receptors, G protein-coupled receptors, enzyme-linked receptors
- Enzyme-linked: receptors with tyrosine kinase activity, serine/threonine kinase activity, guanylate cyclase activity

G protein-coupled receptors (GPCRs)

Receptors usually consist of 7 trans-membrane α-helices (TM).
Combine with ligands and signal to secondary signaling molecules.
Signal transmission is usually much slower and more complex than ion-channel-coupled receptors.
Often act as intermediaries to carry signals from the 7TM receptor to the effector.
Classify based on alpha (α) subunit type: Stimulating (Gs), Inhibitory (Gi)

Signal Transduction

The signaling process consists of signaling molecules (ligands); ligands binding to receptor(s); and intracellular signaling molecules being produced.
This triggers intracellular reactions and, ultimately transmits the signal to the effector protein.
Features: cascade and amplification, and molecular relay race.

Molecular Switches

Many signaling molecules act as molecular switches because they switch between active and inactive states in response to receiving a signal.
Proteins:
- have activity turned on or off by adding or removing phosphate groups
- have activity that depends on GDP and GTP exchange
Types include protein kinase and G proteins.

Proteasome Functions

Proteasomes are large, high-molecular-weight enzyme complexes.
Found in eukaryotic cells cytoplasm and nucleus.
Bind to proteins bound to ubiquitin
Unfold a protein and bring it into the central cylinder in the proteasome
Cut proteins into short peptides and release them

Organelle Degradation (autophagy)

Damaged organelles (e.g. mitochondria, ER, nuclei , and peroxisomes) send signals to form autophagosomes.
Enclosing and isolating organelles in an autophagosome.
Degradation in secondary lysosomes (autolysosomes).
Degradation types include nucleus (nucleophagy), mitochondria (mitophagy), lysosome (lysophagy), and ribosome (ribophagy).

Additional Notes

A healthy organism degrades 3-5% of proteins versus in a sick organism, much more.
The number of proteasomes varies and depends on the cell's need for protein breakdown.
Protein degradation in eukaryotic cells occurs in two ways: - lysosomal proteolysis (non-selective) - proteasomal proteolysis (selective) involving the ubiquination process.

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Test your knowledge on key biological concepts related to the human genome, cellular structures, and organic molecules. This quiz covers nucleolar organizer regions, endoplasmic reticulum functions, and the characteristics of carbohydrates and lipids. Challenge yourself and see how well you understand the building blocks of life.