Cell Structure & Components

Q: What are the major difference between Plants and Animals at the Cellular Level?

A:

Animal Cell - cytoplasm, nucleus, cell membrane, mitochondria

Plant Cell - cytoplasm, nucleus, cell membrane, cell wall, mitochondria, permanent vacuole, chloroplast

• There are two groups of kingdoms + six kingdoms

  • Eukaryote

    • Animalia

    • Fungi

    • Plantae

    • Protista

  • Prokaryote

    • Archaea

    • Bacteria

Core Concept Summary

1. Cell Membranes are composed of lipids, proteins, and carbohydrates

2. The Plasma Membrane is a selective barrier that controls the movement of molecules between the inside and the outside of the cell

3. The Endomembrane System is an interconnected system of membranes that includes the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysomes, vesicles, and plasma membrane

4. Mitochondria and Chloroplasts are organelles involved in harnessing energy and likely evolved from free-living prokaryotes

Cell Theory

• all organisms are made up of cells

• the cell is the fundamental unit of life

• cells come from preexisting cells → cells make cells

  • complicated, have inner workings that serve a lot of functions

• proposal; the size of an organism scales with its complexity → if an organism has more cell numbers, it has that many cellular types

• cells have various shapes and serve diverse functions

• during evolution, cells can either gain or lose functions

Tools Used to Study Cells

• are

  • Electron microscope

  • Light Microscope

  • the naked eye can see a cell up to a minimal size of 100 micrometers

Cell Membranes

• are composed of lipids, proteins, and carbohydrates

• not all cells have cell walls - but they have membranes

Phospholipids

• major component of the cell membrane

• they are amphipathic - both hydrophilic + hydrophobic

• possess a hydrophilic head + hydrophobic tails → important

Lipid Structures

• Micelle - head is large and bulky with one hydrophobic tail buried

• Bilayer - head is small but with two hydrophobic tails

• Liposome - phospholipids spontaneously form enclosed bilayers called liposomes

  • have a space in the middle where a ‘drug’ can be placed to deliver medicine into the body

Cholesterol

• a component of animal cell membranes

• can also increase or decrease membrane fluidity depending on the temperature

  • at a normal temperature → will reduce the fluidity of the membrane

  • at low temperatures → prevents the phospholipids from packing together tightly, increases fluidity

• has an amphipathic structure which allows it to pack tightly with phospholipids

• attaches to the head of the lipid like the tails

• possess a hydrophobic head group (-OH), hydrophobic rigid planar group of rings, and a hydrophobic hydrocarbon tail (-CH3CH3CH3)

Protein In The Membrane

• Transporters - move ions or molecules across the membrane; permanently fixed into the cell membrane

• Receptors - allow the cell to receive signals from the environment

• Enzymes - catalyze the chemical reactions

• Anchors - attach to other proteins that help maintain cell structure and shape

Integral and Peripheral Proteins

• Integral Membrane Proteins - are permanently associated with cell membranes; cannot be removed from the cell membrane without destroying it

• Peripheral Membrane Proteins - are temporarily associated with the lipid bilayer or with integral membrane proteins through weak noncovalent interactions; can be removed

Is The Cell Membrane Impermeable?

• the plasma membrane is a selective barrier that controls the movement of molecules between the inside and the outside of the cell

Diffusion

• the simplest movement into and out of cells is passive transport which works by diffusion

• solute moves from a high concentration to a low concentration

• Simple Diffusion - small molecules diffuse through the membrane

• Facilitated Diffusion - large molecules are assisted by the protein channels and carriers

Osmosis

• the diffusion of water

• higher solute concentration, lower water concentration : lower solute concentration, higher water concentration

• the membrane allows the passage of water but not the solute

Effects of Osmosis

• Red Blood Cell Example

  • Hypertonic: a solution with a higher solute concentration than the cell, water will leave the cell by osmosis then the cell will shrink

  • Isotonic: a solution with the same solute and water concentration as the blood cell, the cell will maintain its shape

  • Hypotonic: a solution that has a lower solute concentration, water will move into the cell

  • Very Hypotonic: a solution that has a very low solute concentration, water will be taken into the cell to the extent that it will explode

Passive and Active Transport

• ATP - provides energy to the cell to support activities within the cell

• Passive Transport - works when the move is consistent with the concentration gradient; higher concentration to a lower concentration

• Active Transport - works when the move is against the concentration gradient; lower concentration to a higher concentration

Primary Active Transport

• uses ATP to move potassium and sodium ions against the concentration gradient

• the sodium and potassium ions move in opposite directions, so the pump is an antiporter

• the transporters that move two molecules in the came direction are symporters or co-transporters

Secondary Active Transport

• relies on the Primary Active Transport which will create an electrochemical gradient

• pumps protons across the cell membrane using ATP to create a proton concentration, these protons are charged and create an electric gradient

• the movement of the protons will promote the movement of coupled molecules

• the movement of the coupled molecule is driven by the movement of protons and not direct ATP

The Endomembrane System

• an interconnected system of membranes that includes the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysomes, vesicles, and plasma membrane

• organelles within a cell are connected and communicate with one another

• Vesicle - the transport substances between organelles; will fuse with the plasma membrane and will deliver the contents from the extracellular space to the intracellular space

  • Exocytosis - a vesicle that has budded off from the endomembrane system can fuse with the plasma membrane and deliver its contents into the extracellular space

  • Endocytosis - material from outside the cell is brought into a vesicle that can then fuse with other organelles

  • there are calcium ions that trigger vesicle function

The Nuclear Envelope (The Nucleus)

• stores the cells DNA

• perforated by nuclear pores that allow molecules to move in and out of the nucleus - allow the nucleus to communicate with the rest of the cell

The Endoplasmic Reticulum

• a large organelle in most eukaryotic cells and it produces many of the lipids and proteins inside and outside the cell

• The Rough ER - associated with ribosomes, many proteins are synthesized here by ribosomes associated with the rough ER

  • surrounds the nuclear envelope

• The Smooth ER - lacks ribosomes and are the primary site of lipid synthesis

The Golgi Appartus

• the next stop for vesicles after the ER

• further modifies proteins and lipids from the ER

• to sort proteins and lipids as they move to their final destination

• to synthesis the cells carbohydrates

Lysosomes

• specialized vesicles derived from the Golgi Apparatus

• they degrade proteins, nucleic acids, lipids, and complex carbohydrates

The Mitochondria and Chloroplasts

• separate from the Endomembrane System

• organelles involved in harnessing energy and likely evolved from free-living prokaryotes

• are found outside the eukaryotic cells but are believed to have been captured and evolved inside the eukaryotic cells at one point

Plant Cell Wall and Vacuoles

• Cell Wall - surrounds the cell membrane and maintain its shape as the cell takes in water

  • Turgor Pressure - the force exerted by water pressing against an object

  • how is turgor pressure important?

    • fungi use turgor pressure to perform pathogenesis