Prokaryotes, Eukaryotes and cell size - Ignition

Ignition notes flashcards.

Cell theory

1. All organisms are composed of more than 1 cell.

2. Smallest unit that is capable of performing life functions.

3. A new cell came from division of previous cells.

Key features of cells

• Surrounded by a membrane

• Carry out specialised functions

• MUST replicate DNA

• MUST synthesise their cellular components, e.g., proteins

• Carry out metabolic processes, e.g., cellular respiration

Eukaryotic cells

Contain a nucleus and other organelles that are bound by membranes. Found in animals and plants, larger than prokaryotic cells.

Organelles exist to work together in order to package, modify, and export proteins.

DNA - LINEAR STRUCTURE IN NUCLEUS

Prokaryotic cells

A type of cell lacking a membrane-enclosed nucleus and membrane-enclosed organelles; found only in the domains Bacteria and Archaea. Smaller than Eukaryotic Cells.

No membrane-bound organelles.

DNA—SINGLE CIRCULAR STRUCTURE IN CHROMOSOME

Cell Organelles

Mostly surrounded by a membrane. Controls movement of substance between organelle and cytosol. Allows processes that require different environments to occur at the same time, e.g., enzymes and reactants.

SA:V (Surface area to volume ratio)

Surface Area (SA) - measurement of outer surface

Volume (V) : the amount of space occupied by an object

SA:V - a comparison of the surface area to the volume of an object.

Formula: SA = A(L²)*6, V = L³, L = Length

Size of cell limited.

How to increase SA:V?

1. Have a ‘frilly‘ (like fur) edge;

2. Being long and narrow.

A high SA:V

Increases the rate at which substances can diffuse in and out of a cell.

A smaller organism will have a

Consequently, a larger organism will have a

High SA:V

Low SA:V

When the SA:V ratio becomes too low a cell

It will not be able to exchange materials with its environment efficiently. Specialized tissues and body systems required in order to efficiently exchange substances.

Cytosol

Liquid part of cell, NOT including organelles. Both Eukaryotic and Prokaryotic Cells. Both animal/plant cells.

Cytoplasm

A jellylike fluid inside the cell in which the organelles are suspended, including organelles and cytosol. Both prokaryotes and eukaryotes. Aqueous. Both animal/plant cells.

Ribosomes

The site of protein synthesis. Both prokaryotes and eukaryotes. Both animal/plant cells.

Plasma Membrane

Barrier made of phospholipid bilayer—regulates the movement of substances in/out of the cell, maintaining the in-cell environment. Semi-pemerable (allows some to in/out). Both Eukaryotic and Prokaryotic Cells. Both animal/plant cells.

Nucleus

A part of the cell containing DNA and RNA and responsible for growth and reproduction. Eukaryotic only. Both Animal/plant cells.

Rough Endoplasmic Reticulum

Folding of proteins and packaging of proteins into vesicles for going out of cells. Ribosomes attached - vesicles carry proteins to golgi appratus. Eukaryotic only. Both animal/plant cells.

Smooth Endoplastic Reticulum

Site of lipid (fat) synthesis. Eukaryotic only. Both animal/plant cells.

Golgi Body (Golgi Apparatus)

Modify and packaging of proteins into vesicles for going out of cells. Eukaryotic only. Both animal/plant cells.

Mitochondria

Site of aerobic cellular respiration (where most of A denosine triphosphate (ATP) is made). Eukaryotic only. Both animal/plant cells.

Chloroplast

Site of photosynthesis; stacked pancake structure, unlike Mitochondria. Eukaryotic Cells ONLY. Plant cells ONLY.

Vacuole

Stores water/other substances important in plant cells. Similar to nucleus, but empty. Eukaryotic cells ONLY. BOTH ANIMAL (seperate, small ones) AND PLANT CELLS (LARGE ones).

Cell wall

Presents plant cells from expanding and rupturing of plasma membrane. Eukaryotic Cells ONLY. Plant cells ONLY.

Note: ALL plant cells have cell wall but NOT all of them have chloroplasts.

Lysosomes

A membrane-bound cell organelle that contains digestive enzymes. EUKARYOTIC only. ANIMAL only.

Adenosine triphosphate (ATP)

The source of energy for use and storage at the cellular level.

Structure of Plasma Membrane

Main Components: Phospholipid molecule—phosphate head and two fatty acid tails.

Chemical Property:

Phosphate head—hydrophilic (soluble/attracted to water), POLAR

Fatty acid tails - hydrophobic (insoluble/repel water), NON-POLAR

Phosphate head faces extracellular space and cytoplasm—both aqueous.

Fluid-Mosaic Model: 1972

Fluid: Proteins and individual phospholipids are not fixed but can move within the bilayer.

Mosaic— these molecules including different types of molecules (phospholipids), proteins, cholesterol, carbohydrates, etc.

Transportation of matters across the plasma membrane

In - carbohydrates (e.g., glucose), amino acids/proteins, fats, ions, gases, H2O.

Out—waste (e.g., urea), ions, gases, H2O.

Polar vs Non-Polar Molecules

Polar molecules: contain a slightly ± charged end. e.g., H2O

Non-polar molecules: does not contain a ± charged end.

Passive Movement

Movement of particles from high concentration to low concentration without ATP (energy).

Includes diffusion, facilitated diffusion, and osmosis.

Diffusion

Net movement: high→low concentration until equilibrium (same number of particles). NO ATP.

Rate of diffusion affected by temperature (rate of reaction ;).

Facilitated Diffusion

Protein-assisted (from protein channel for small hydrophilic and carrier protein for large hydrophobic) movement of particles high → low concentration, no ATP; rate affected by temperature.

Osmosis

A type of diffusion that specifically describes the movement of water molecules ONLY.

Occurs when H2O concentration ≠ Cytosol

Net movement: high H2O concentration → low. No ATP.

Permeability of plasma membrane

Small uncharged molecules: permeable, e.g., O2, CO2.

Lipid-soluble (hydrophobic, nonpolar): permeable, e.g., alcohol, steroids

Small water-soluble (hydrophilic - OSMOSIS): permeable, e.g., H2O

Ions: non-permeable (only protein channels), e.g., K+, Na+

Larger, polar, water-soluble molecules: non-permeable (only protein channels), e.g., glucose

Structure of Solution

Solution = Solute (e.g., C6H12O6) + Solvent (e.g., H2O)

• Solute: The substance that is dissolved in a solution (can be solid, liquid, or gas).

• Solvent: The substance that dissolves the solute (can be liquid, solid, or gas).

Active Transport

Net movement of substances in/out of cell from low → high concentration (against concentration gradient) through carrier proteins using energy (ATP).

Protein Pumps

Membrane proteins that actively transport ions or molecules using ATP (e.g., sodium-potassium pump).

Cell Concetration vs External Concentration

• Hypertonic: Higher outside → Water out → Cell shrinks.

• Isotonic: Equal inside & outside → No change.

• Hypotonic: Higher inside → Water in → Cell swells.

Endocytosis (Bulk Transport)

Process of taking materials into the cell by forming vesicles from the membrane containing the substance.

Types of Endocytosis

• Phagocytosis: Engulfing solids ("cell eating").

• Pinocytosis: Engulfing liquids ("cell drinking").

Exocytosis (Bulk Transport)

Process where vesicles fuse with the membrane to release contents outside the cell (secreting cells).

Prokaryotic Cell Replication: Binary Fission

Binary fission in prokaryotes involves:

1. Duplication of chromosome – The nucleoid (DNA) is replicated.

2. Duplication of other cellular components – Ribosomes, plasmids (if present), and cell membrane/wall are copied.

3. Cell growth – The cell doubles in size.

4. Cell division – The cell splits into two identical daughter cells. 🚀

Key Points: ALL HAVE A CELL WALL, exponential increase, asexual reproduction (comes from parent, genetically identical).

Stages of the cell cycle (Eukaryotic)

Interphase:

• G0 phase (in some cells)

• Gap 1 – growth, duplicates organelles

• S phase – DNA Replication

• Gap 2 – growth, makes proteins for mitosis

  Mitosis: (PMAT)

• Division of the nucleus

  Cytokinesis:

• Division of the cytoplasm

• Plant and animal cell cytokinesis are different.

  

Mitosis (PMAT) / Cytokinesis

• Early Prophase: Chromosomes condense; nucleolus fades.

• Late Prophase: Chromosomes are visible; centrioles move; spindle fibres attach to centromeres via kinetochores; membrane disassembles.

• Metaphase: Chromosomes align at the equator by spindle fibres.

• Anaphase: Chromosomes pulled apart at centromeres; chromatids pulled apart to the pole of the cell by spindle fibre.

• Telophase: Chromosomes decondense; nucleolus reappears; spindle breaks down; nuclear envelope reforms.

• Cytokinesis: division of cytoplasm that happens right after mitosis. Animals (cleavage furrows) and plants (cell plate) are different.

Spindle Fibres

Spindle fibres are microtubules involved in cell division, attached to centrioles.

They attach to kinetochore proteins (protein complexes on centromere) on sister chromatids.

Align chromosomes at the metaphase plate.

Separate chromatids during anaphase for equal distribution.

Interphase - G0 Phase

At the start of G1, a cell may enter the G0 phase or resting phase:

Cell functions normally but does not grow in size or structure.

Usually temporary (cells re-enter the G1 phase)

Some specialised cells (e.g., nerve cells) remain permanently in G0 phase and do not undergo replication.

Interphase - G1 Phase

Gap 1 phase—Primary growth phase

Cell almost doubles in size; gains energy (ATP)

Cell matures: Synthesises proteins, membranes, and duplicates organelles

If not enough resources to mature, the cell may go into G0 phase until resources are plentiful.

Longest part of interphase

Interphase - S Phase

Synthesis phase:

DNA replication occurs.

Interphase - G2 Phase

Gap 2 phase – Secondary growth phase.

Gains energy (ATP); synthesis of cellular components such as proteins.

Checks DNA:

• Severe mispairing → Apoptosis (cell death).

• Minor mispairing → DNA repair.

Haploid/Diploid

Diploid = 2n (2 sets of chromosomes)

Haploid = n (1 set of chromosomes)

Production of Cell in Cell Cycle

Two genetically identical daughter cells are produced from one parent cell.

Each daughter cell has a diploid number of chromosomes.

Chromosomes in Dividing Cells

• Before Mitosis (S Phase): One chromosome duplicates into two sister chromatids joined at the centromere (still considered one chromosome).

• Anaphase/Telophase: Sister chromatids separate, becoming individual chromosomes, temporarily doubling the chromosome count.

• After Mitosis & Cytokinesis: Each daughter cell has the same chromosome number as the original cell.

• Next S Phase: Chromosomes duplicate again, forming new sister chromatids.

Reasons for Cell Division/Replication

1. Growth/Deveopment;

2. Mantenance and Repair;

3. Restoring the Nucleus-to-Cytoplasm Ratio.