1.1.4
Ultrastructure of Eukaryotic Cells 2
Ribosomes and the Endoplasmic Reticulum
Ribosomes and the Endoplasmic Reticulum
Proteins are made in ribosomes. Proteins may then be folded and processed by the rough endoplasmic reticulum (RER). The smooth endoplasmic reticulum makes and processes lipids.


Structure of ribosomes
Structure of ribosomes
- 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.
- Eukaryotic ribosomes are found in the cytoplasm, attached to the RER, and in mitochondria and chloroplasts.
- Ribosomes in the cytoplasm and RER are 80S in size.
- Ribosomes in mitchondira and chloroplasts are 70S in size.


Function of ribosomes
Function of ribosomes
- Ribosomes are in charge of protein synthesis.
- Protein synthesis is an essential function of all cells. This is why ribosomes are found in practically every cell.


Structure of the ER
Structure of the ER
- The ER is a series of interconnected membranous sacs and tubules.
- The membrane of the ER is a phospholipid bilayer embedded with proteins.
- The smooth ER (SER) membrane has no ribosomes but the rough ER (RER) membrane has many ribosomes on its surface.


Function of the RER and SER
Function of the RER and SER
- The RER is responsible for processing and folding proteins.
- The SER is responsible for making and processing lipids.
The Plasma Membrane and Cell Wall
The Plasma Membrane and Cell Wall
The plasma membrane is a partially-permeable barrier between the cell's interior and its surroundings. The cell wall is a structure external to the plasma membrane found in plant, algal and fungal cells.


Structure of plasma membrane
Structure of plasma membrane
- The fluid mosaic model describes the structure of plasma membranes.
- This model says that plasma membranes are made up of a variety of components (e.g. phospholipids, proteins and cholesterol) that are continuously moving around.
- Phospholipids are the primary component of the membrane. They are well-suited to this role because they are amphipathic (contain hydrophobic and hydrophilic regions).
- The hydrophilic region faces outwards and the hydrophobic region inwards. This means that polar substances can't easily pass through the membrane.


Function of plasma membrane
Function of plasma membrane
- Plasma membranes protect cells from their surrounding environment.
- The selectively-permeable (partially-permeable) nature of plasma membranes means that they can selectively allow certain molecules to pass through and stop others.
- In this way, these membranes mediate the interactions between a cell's interior and its surroundings.
- Plasma membranes play a role in several cellular processes (e.g. cell signalling).
- Plasma membranes are also the attachment point for some extracellular (e.g. cell wall) and intracellular structures (e.g. cytoskeleton).


Microvilli
Microvilli
- Sometimes the plasma membrane forms multiple small projections from its surface.
- These projections are called microvilli. They increase the surface area of the cell.
- These are typical in cells lining the digestive tract, as the increases surface area speeds up absorption.


Structure of cell walls
Structure of cell walls
- The cell wall is a rigid covering that protects the cell.
- Plant, fungal and algal cells all have cell walls.
- The major organic molecule in fungal cell walls is chitin.
- Plant and algal cell walls are made of cellulose.
- Cellulose is a polysaccharide made up of glucose units.


Function of cell walls
Function of cell walls
- The cell wall provides structural support and gives shape to the cell.
- Plasmodesmata are thin cytoplasmic connections that run through the cell wall of plant cells.
- Plasmodesmata link neighboring plant cells through the cell wall to allow communication.
Centrioles, Flagella and Cilia
Centrioles, Flagella and Cilia
Centrioles play an important role in cellular division and organisation. They are also very important in the synthesis of cilia and flagella.


Structure of centrioles
Structure of centrioles
- Centrioles have a cylindrical shape. They are made up of parallel microtubules that surround a central cavity.
- In most eukaryotic cells, centrioles are found as pairs that are arranged at right angles to one another.
- Centrioles are only found in isolation when in the basal regions of flagella and cilia.


Function of centrioles
Function of centrioles
- Centrioles are a key component of centrosomes, which are crucial for organising microtubules in the cell.
- Centrioles help to organise the mitotic spindle during cell division.


Structure of flagella
Structure of flagella
- Flagella are hair-like structures.
- Eukaryotic flagella are described as having a nine-plus-two arrangement (nine pairs of microtubules surrounding a central pair of microtubules). All of the microtubules are made from the protein tubulin.
- Bacterial flagella are helical and are mainly made up of the protein flagellin.


Function of flagella
Function of flagella
- Flagella are used by some organisms for locomotion.
- Eukaryotic flagella generate propulsion using a whipping motion.
- Bacterial flagella generate propulsion by moving in a propeller-like way.


Structure of cilia
Structure of cilia
- Like flagella, cilia have a central core called the axoneme.
- Primary cilia have a nine-plus-zero arrangement.
- Motile cilia have a nine-plus-two arrangement.


Function of cilia
Function of cilia
- Cilia generate the locomotion of the phylum Ciliophora.
- Cilia can also help to move substances internally in organisms by synchronising their beating.
1Cell Structure
1.1Cell Structure
1.1.1Studying Cells - Microscopes
1.1.2Introduction to Eukaryotic & Prokaryotic Cells
1.1.3Ultrastructure of Eukaryotic Cells
1.1.4Ultrastructure of Eukaryotic Cells 2
1.1.5Ultrastructure of Eukaryotic Cells 3
1.1.6Prokaryotic Cells
1.1.7Viruses
1.1.8End of Topic Test - Cell Structure
1.1.9Exam-Style Question - Microscopes
1.1.10A-A* (AO2/3) - Cell Structure
2Biological Molecules
2.1Testing for Biological Modules
2.2Carbohydrates & Lipids
2.3Proteins
3Enzymes
4Cell Membranes & Transport
4.1Biological Membranes
5The Mitotic Cell Cycle
6Nucleic Acids & Protein Synthesis
6.1Nucleic Acids
7Transport in Plants
8Transport in Mammals
8.1Circulatory System
8.2Transport of Oxygen & Carbon Dioxide
9Gas Exchange
9.1Gas Exchange System
10Infectious Diseases
10.1Infectious Diseases
10.2Antibiotics
11Immunity
12Energy & Respiration (A2 Only)
13Photosynthesis (A2 Only)
14Homeostasis (A2 Only)
14.1Homeostasis
14.2The Kidney
14.3Cell Signalling
14.4Blood Glucose Concentration
14.5Homeostasis in Plants
15Control & Coordination (A2 Only)
15.1Control & Coordination in Mammals
15.1.1Neurones
15.1.2Receptors
15.1.3Taste
15.1.4Reflexes
15.1.5Action Potentials
15.1.6Saltatory Conduction
15.1.7Synapses
15.1.8Cholinergic Synnapses
15.1.9Neuromuscular Junction
15.1.10Skeletal Muscle
15.1.11Sliding Filament Theory Contraction
15.1.12Sliding Filament Theory Contraction 2
15.1.13Menstruation
15.1.14Contraceptive Pill
15.2Control & Co-Ordination in Plants
16Inherited Change (A2 Only)
16.1Passage of Information to Offspring
16.2Genes & Phenotype
17Selection & Evolution (A2 Only)
17.2Natural & Artificial Selection
18Classification & Conservation (A2 Only)
18.1Biodiversity
18.2Classification
19Genetic Technology (A2 Only)
19.1Manipulating Genomes
19.2Genetic Technology Applied to Medicine
19.3Genetically Modified Organisms in Agriculture
Jump to other topics
1Cell Structure
1.1Cell Structure
1.1.1Studying Cells - Microscopes
1.1.2Introduction to Eukaryotic & Prokaryotic Cells
1.1.3Ultrastructure of Eukaryotic Cells
1.1.4Ultrastructure of Eukaryotic Cells 2
1.1.5Ultrastructure of Eukaryotic Cells 3
1.1.6Prokaryotic Cells
1.1.7Viruses
1.1.8End of Topic Test - Cell Structure
1.1.9Exam-Style Question - Microscopes
1.1.10A-A* (AO2/3) - Cell Structure
2Biological Molecules
2.1Testing for Biological Modules
2.2Carbohydrates & Lipids
2.3Proteins
3Enzymes
4Cell Membranes & Transport
4.1Biological Membranes
5The Mitotic Cell Cycle
6Nucleic Acids & Protein Synthesis
6.1Nucleic Acids
7Transport in Plants
8Transport in Mammals
8.1Circulatory System
8.2Transport of Oxygen & Carbon Dioxide
9Gas Exchange
9.1Gas Exchange System
10Infectious Diseases
10.1Infectious Diseases
10.2Antibiotics
11Immunity
12Energy & Respiration (A2 Only)
13Photosynthesis (A2 Only)
14Homeostasis (A2 Only)
14.1Homeostasis
14.2The Kidney
14.3Cell Signalling
14.4Blood Glucose Concentration
14.5Homeostasis in Plants
15Control & Coordination (A2 Only)
15.1Control & Coordination in Mammals
15.1.1Neurones
15.1.2Receptors
15.1.3Taste
15.1.4Reflexes
15.1.5Action Potentials
15.1.6Saltatory Conduction
15.1.7Synapses
15.1.8Cholinergic Synnapses
15.1.9Neuromuscular Junction
15.1.10Skeletal Muscle
15.1.11Sliding Filament Theory Contraction
15.1.12Sliding Filament Theory Contraction 2
15.1.13Menstruation
15.1.14Contraceptive Pill
15.2Control & Co-Ordination in Plants
16Inherited Change (A2 Only)
16.1Passage of Information to Offspring
16.2Genes & Phenotype
17Selection & Evolution (A2 Only)
17.2Natural & Artificial Selection
18Classification & Conservation (A2 Only)
18.1Biodiversity
18.2Classification
19Genetic Technology (A2 Only)
19.1Manipulating Genomes
19.2Genetic Technology Applied to Medicine
19.3Genetically Modified Organisms in Agriculture
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