Cell Structure–Seneca Flashcards
Similarities of Prokaryotic and Eukaryotic Cells
- Both contain organelles.
- The cell-surface membrane made of phospholipid bilayer–responsible for controlling the passage of substances across exchange surfaces.
Prokaryotes
Prokaryotes are simple, single-celled organisms.
Eukaryotes
Eukaryotes are complex, multicellular organisms.
Differences of Prokaryotic and Eukaryotic Cells
• Prokaryotic cells–single-celled prokaryotic organisms.
• Eukaryotic cells make up complex eukaryotic organisms.
• Eukaryotic cells are larger and more complex than prokaryotic cells.
• Cells arise from other cells by:
- binary fission in prokaryotic cells
- mitosis or meiosis in eukaryotic cells.
Animal Cell
Contains: – Mitochondria. – Ribosomes. – Endoplasmic reticulum (ER). – Golgi. – Lysosomes. – Nucleus. – Animal cells are enclosed by a cell membrane.
Plant Cell
Contains: – Mitochondria. – Ribosomes. – Endoplasmic reticulum (ER). – Golgi. – Lysosomes. – Nucleus. – Plant cells also possess: – Vacuole (a repository of cell sap). – Chloroplasts (the site of photosynthesis). – Cell wall (made of cellulose and contains plasmodesmata, through which cells exchange substances with each other).
Algal Cells
Contains: – Mitochondria. – Ribosomes. – Endoplasmic reticulum (ER). – Golgi. – Lysosomes. – Nucleus. – Vacuole (a repository of cell sap). – Chloroplasts (the site of photosynthesis). – Cell wall (made of cellulose and contains plasmodesmata, through which cells exchange substances with each other).
Fungal cells
Contains: – Mitochondria. – Ribosomes. – Endoplasmic reticulum (ER). – Golgi. – Lysosomes. – Nucleus. – Vacuole (a repository of cell sap). – Cell wall (made from chitin)
Cell Specialisation
A cell specialises because the shape and contents of a cell help it to carry out its function.
Examples include:
• Muscle cells–active–contain lots of mitochondria–produce ATP.
Cell Organisation
• Specialised cells are organised into tissues to organs to organ systems.
Structure and Function of Plasma Membrane
Structure
• Made from a phospholipid bilayer.
• Have proteins and cholesterol embedded in them.
• Proteins can act as receptors–cell can respond to the external environment of the cell.
Function
• Controls the passage of organic molecules, ions, water, and oxygen into and out of the cell.
• Waste products leave the cell by passing through the plasma membrane.
Structure and Function of Cytoplasm
Structure
• Made up of organelles suspended in the gel-like cytosol.
• 70% made up of water.
• Also contains proteins, sugars, ions and fatty acids.
Functions
• Many metabolic reactions take place.
• Different organelles perform specific functions.
Nucleus
A big organelle that contains the cell’s DNA. It is surrounded by a nuclear envelope.
Structure and Function of Nuclear Envelope
Structure
• The double-membrane structure that has a number of pores.
• Both the inner and outer membranes are phospholipid bilayers.
Function
• The pores control the passage of ions, molecules and RNA between the nucleoplasm and cytoplasm.
Structure and Function of Nucleus
Structure
• The nucleoplasm is the semi-solid fluid inside the nucleus, where we find the chromatin and the nucleolus.
• In eukaryotes, the nucleus contains linear chromosomes that are made up of DNA.
• There is an area within the nucleus called the nucleolus (plural = nucleoli).
Function
• Controls the actions of the cell.
• DNA contains instructions for the synthesis of proteins.
• Ribosomal RNA is joined together with associated proteins in the nucleolus to assemble the ribosomal subunits.
Mitochondria
Mitochondria produce adenosine triphosphate (ATP) via aerobic respiration.
Structure and Function of Mitochondria
Structure
• Oval-shaped, double-membrane organelles that have their own ribosomes and DNA.
• Each membrane is a phospholipid bilayer embedded with proteins.
• The inner layer of the membrane has folds called cristae.
• The area surrounded by the folds is called the mitochondrial matrix–contains enzymes used for respiration.
Function
• Mitochondria make ATP via aerobic respiration.
• Muscle cells–high concentration of mitochondria–highly active–need energy–keep body moving.
Structure and Function of Chloroplasts
Structure
• Have own DNA, ribosomes and have inner and outer membranes.
• The space enclosed by the inner membrane contains a set of interconnected and stacked fluid-filled membrane sacs called thylakoids.
• Each stack is called a granum (plural = grana).
• Grana are linked by lamellae.
• Lamellae are flat, thin parts of thylakoid membrane.
• The fluid enclosed by the inner membrane that surrounds the grana is called the stroma.
Function
• Photosynthesis happens in chloroplasts and allows plants to make their own food.
• Found in plant and algal cells but not in animal cells.
Chloroplasts
Chloroplasts are plant cell organelles that carry out photosynthesis.
Structure and Function of the Golgi Apparatus
Structure
• Series of flattened membranous sacs.
Function
• Transport vesicles form from the endoplasmic reticulum and fuse with the Golgi apparatus.
• Empty proteins and lipids into the lumen of the Golgi apparatus.
• As the proteins and lipids travel through the Golgi, they are sorted, packaged and tagged to be sent to the right place.
Structure and Function of the Golgi Vesicles
Structure
• Membrane-bound, fluid-filled vesicles.
• Small, round and are seen in a high density near the edges of the sacs.
• Lysosomes are a type of Golgi vesicle.
Function
• Golgi vesicles store and transport modified proteins and lipids.
• Lysosomes are a special type of Golgi vesicle. They contain enzymes called lysozymes.
• Lysozymes aid the breakdown of proteins, polysaccharides, lipids, nucleic acids and old organelles.
The Functioning of the Golgi Apparatus (steps)
- Transport vesicles from the ER and fuse with the Golgi apparatus
- Empty their contents into the lumen of the Golgi apparatus
- As the proteins and lipids travel through the Golgi, they undergo further modifications that allow them to be sorted
- Newly modified proteins and lipids are packaged into secretory vesicles that bud from the Golgi
Ribosomes and the Endoplasmic Reticulum
Proteins are made in ribosomes. Proteins may then be folded and processed by the RER. The SER makes and processes lipids.
Structure and Function of Ribosomes
Structure
• Ribosomes can be free floating in the cytoplasm or attached to the cytoplasmic side of the endoplasmic reticulum (ER).
• Ribosomes are very small organelles made of protein subunits. This means that ribosomes are NOT covered by a membrane.
Function
•Protein synthesis.
• Protein synthesis is an essential function of all cells. Found in practically every cell.
Structure and Function of Endoplasmic Reticulum
Structure
• Series of interconnected membranous sacs and tubules.
• The membrane of the ER is a phospholipid bilayer embedded with proteins.
• The SER membrane has no ribosomes but the RER membrane has many ribosomes on its surface.
Function
• The RER is responsible for processing and folding proteins.
• The SER is responsible for making and processing lipids.
Cell Wall
The cell wall is a structure external to the plasma membrane.
Structure and Function of Cell Walls
Structure
• The cell wall is a rigid covering that protects the cell.
• Plant, fungal and algal cells all have cell walls.
• Cellulose is a polysaccharide made up of glucose units.
Function
• Provides structural support and gives shape to the cell.
Structure and Function of Cell Vacuoles
Structure
• Occupies most of the area of the cell.
• These vacuoles are surrounded by a membrane called the tonoplast and contain a weak solution of salts and sugars called cell sap.
• Cell vacuoles are found in the cytoplasm of plant cells but are NOT present in animal cells.
Function
• Allows the cell to remain rigid.
• Holds more water, the vacuole pushes against the cell wall and pressure is maintained. Stops the plant from wilting.
Cell Vacuole
Cell vacuoles are found in plant cell cytoplasm.
DNA in prokaryotes
- Found in a circular molecule.
- Some have smaller loops of DNA called plasmids.
- Bacteria can exchange plasmids with other bacteria, sometimes receiving beneficial new genes.
- Antibiotic resistance often spreads through a bacterial colony through plasmid exchange.
Prokaryotes vs Eukaryotes
Features common to these types of cells are:
• A plasma membrane.
• Cytoplasm.
• DNA.
• Ribosomes (ribosomes are smaller in prokaryotes).
Main difference in terms of organelles is that prokaryotes do NOT have any membrane-bound organelles.
Ribosome Productions
- Ribsomnal RNA joins with proteins–form ribsomnal subunits
- Subunits formed in the nucleolus
- Exit via the pores in the nuclear envelope
Cell Fractionation
Cell fractionation separates organelles according to size to allow them to be studied in an electron microscope.
Steps of Cell Fractionation
1) Homogenisation
• Sample is homogenised using a blender to break the cells.
2) Filtration
• Sample is filtered into tubes through a gauze.
• Gauze separates larger components from the smaller organelles.
• Filtered into tubes to be fractionated using ultracentrifugation.
3) Ultracentrifugation
• Spun at a low speed in a centrifuge.
• Each tube must be balanced with another tube directly opposite for the centrifuge to work properly.
• Separates the sample into fractions.
• Heavier organelles are forced to the bottom of the tube.
• Lighter organelles move towards the top.
• Cell debris forms a pellet at the bottom of the tube, leaving the supernatant above it that contains the organelles.
• The supernatant is poured off and centrifuged at a higher speed to separate the next heaviest organelles (the nuclei).
• This is repeated at increasingly higher speeds to separate each fraction.
4) Order of fractionation
• The process of repeated ultracentrifugation produces factions of cell organelles from heaviest to lightest.
Organelles in the order of heaviest to lightest
- Nucleus.
- Chloroplasts.
- Endoplasmic reticulum.
- Mitochondria.
- Lysosomes.
- Ribosomes.
In what conditions should the tissue sample be kept in (for cell fractionation)?
- Ice cold (reduces enzyme activity that might damage organelles).
- Isotonic solution (prevents osmosis that could shrink or burst organelles).
- No osmosis takes place in isotonic solution.
- Buffered solution (avoids damaging the protein structures).
