Triglycerides & Phospholipids

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Triglycerides

Triglycerides are a type of lipid that are mainly used as energy storage molecules.

Formation of triglycerides

Triglycerides are formed by the condensation of one molecule of glycerol and three molecules of fatty acid.
- Ester bonds form between the glycerol and the fatty acid chains.
- One water molecule is released per ester bond.
  - So, three molecules of water are released per triglyceride formed.

Structure of fatty acids

Fatty acids have long 'tails' made of a chain of hydrocarbons with 4-36 carbon atoms.
The hydrocarbon tail is variable but most fatty acids contain 12-18 carbons.
Glycerol links to the central carbon atom on fatty acids.

Types of fatty acids

The three fatty acids in the triglyceride may be similar or dissimilar.
Fatty acids may be saturated or unsaturated.
Some fatty acids have names that come from their origin.
- E.g. Palmitic acid is a saturated fatty acid that comes from the palm tree.

Functions of Triglycerides

The structures of triglycerides are related to their functions as molecules responsible for storing energy.

Triglycerides in energy release

Chemical energy is stored in the fatty acid hydrocarbon tails.
So, lots of energy is released when triglycerides are broken down.

Lipids contain lots of energy

Carbohydrates contain half the amount of energy per gram as lipids do.

Triglycerides repel water

Triglycerides are insoluble in water because the fatty acid tails are hydrophobic.
This means that the cell's water potential is NOT affected by triglycerides.
- This is important because if triglycerides didn't repel water, the water would enter the cell through the process of osmosis. This would make the cells swell up.

Lipid droplets

In cells, the insoluble triglycerides crowd together as droplets because the hydrophobic fatty acid tails face inwards.

Phospholipids

Phospholipids are a type of lipid that forms a bilayer. They are the main component of cell membranes and are responsible for controlling what goes into and out of cells.

Structure of phospholipids

Phospholipids and triglycerides are quite similar. They are both composed of fatty acid chains attached to glycerol.
The main difference is that one of the three hydrophobic fatty acid tails is replaced by a hydrophilic phosphate group in phospholipids.
This means that a phospholipid molecule has a hydrophobic and hydrophilic part.
- This kind of molecule is called an amphipathic molecule.

Hydrophobic tail

Phospholipids have two fatty acid chains.
The two fatty acid chains in phospholipids are hydrophobic and cannot interact with water.
In membranes, the hydrophobic fatty acid tails face inwards in the bilayer.
- This means that water-soluble substances can't easily pass through the membrane.

Hydrophilic head

The modified phosphate group in phospholipids is hydrophilic and can interact with water.
In membranes, the hydrophilic phosphate group faces the outside.

Phospholipid diagram

1Biological Molecules

1.1Monomers & Polymers

1.1.1Monomers & Polymers

1.1.2Condensation & Hydrolysis Reactions

1.2Carbohydrates

1.2.1Structure of Carbohydrates

1.2.2Types of Polysaccharides

1.2.3End of Topic Test - Monomers, Polymers and Carbs

1.2.4Exam-Style Question - Carbohydrates

1.2.5A-A* (AO3/4) - Carbohydrates

1.3Lipids

1.3.1Triglycerides & Phospholipids

1.3.2Types of Fatty Acids

1.3.3Testing for Lipids

1.3.4Exam-Style Question - Fats

1.3.5A-A* (AO3/4) - Lipids

1.4Proteins

1.4.1The Peptide Chain

1.4.2Investigating Proteins

1.4.3Primary & Secondary Protein Structure

1.4.4Tertiary & Quaternary Protein Structure

1.4.5Enzymes

1.4.6Factors Affecting Enzyme Activity

1.4.7Enzyme-Controlled Reactions

1.4.8End of Topic Test - Lipids & Proteins

1.4.9A-A* (AO3/4) - Enzymes

1.4.10A-A* (AO3/4) - Proteins

1.5Nucleic Acids

1.5.1DNA & RNA

1.5.2Polynucleotides

1.5.3DNA Replication

1.5.4Exam-Style Question - Nucleic Acids

1.5.5A-A* (AO3/4) - Nucleic Acids

1.6ATP

1.6.1Structure of ATP

1.6.2End of Topic Test - Nucleic Acids & ATP

1.7Water

1.7.1Structure & Function of Water

1.7.2A-A* (AO3/4) - Water

1.8Inorganic Ions

1.8.1Inorganic Ions

1.8.2End of Topic Test - Water & Inorganic Ions

2Cells

2.1Cell Structure

2.1.1Introduction to Cells

2.1.2Eukaryotic Cells & Organelles

2.1.3Eukaryotic Cells & Organelles 2

2.1.4Prokaryotes

2.1.5A-A* (AO3/4) - Organelles

2.1.6Methods of Studying Cells

2.1.7Microscopes

2.1.8End of Topic Test - Cell Structure

2.1.9Exam-Style Question - Cells

2.1.10A-A* (AO3/4) - Cells

2.2Mitosis & Cancer

2.2.1Mitosis

2.2.2Investigating Mitosis

2.2.3Cancer

2.2.4A-A* (AO3/4) - The Cell Cycle

2.3Transport Across Cell Membrane

2.3.1Cell Membrane Structure

2.3.2A-A* (AO3/4) - Membrane Structure

2.3.3Diffusion

2.3.4Osmosis

2.3.5Active Transport

2.3.6End of Topic Test - Mitosis, Cancer & Transport

2.3.7Exam-Style Question - Membranes

2.3.8A-A* (AO3/4) - Membranes & Transport

2.3.9A-A*- Mitosis, Cancer & Transport

2.4Cell Recognition & the Immune System

2.4.1Immune System

2.4.2The Immune Response

2.4.3Antibodies

2.4.4Primary & Secondary Response

2.4.5Vaccines

2.4.6HIV

2.4.7Ethical Issues

2.4.8End of Topic Test - Immune System

2.4.9Exam-Style Question - Immune System

2.4.10A-A* (AO3/4) - Immune System

3Substance Exchange

3.1Surface Area to Volume Ratio

3.1.1Size & Surface Area

3.1.2A-A* (AO3/4) - Cell Size

3.2Gas Exchange

3.2.1Single-Celled Organisms

3.2.2Multicellular Organisms

3.2.3Control of Water Loss

3.2.4Human Gas Exchange

3.2.5Ventilation

3.2.6Dissection

3.2.7Measuring Gas Exchange

3.2.8Lung Disease

3.2.9Lung Disease Data

3.2.10End of Topic Test - Gas Exchange

3.2.11A-A* (AO3/4) - Gas Exchange

3.3Digestion & Absorption

3.3.1Overview of Digestion

3.3.2Digestion in Mammals

3.3.3Absorption

3.3.4End of Topic Test - Substance Exchange & Digestion

3.3.5A-A* (AO3/4) - Substance Ex & Digestion

3.4Mass Transport

3.4.1Haemoglobin

3.4.2Oxygen Transport

3.4.3The Circulatory System

3.4.4The Heart

3.4.5Blood Vessels

3.4.6Cardiovascular Disease

3.4.7Heart Dissection

3.4.8Xylem

3.4.9Phloem

3.4.10Investigating Plant Transport

3.4.11End of Topic Test - Mass Transport

3.4.12A-A* (AO3/4) - Mass Transport

4Genetic Information & Variation

4.1DNA, Genes & Chromosomes

4.1.1DNA

4.1.2Genes

4.1.3A-A* (AO3/4) - DNA

4.2DNA & Protein Synthesis

4.2.1Protein Synthesis

4.2.2Transcription & Translation

4.2.3End of Topic Test - DNA, Genes & Protein Synthesis

4.2.4Exam-Style Question - Protein Synthesis

4.2.5A-A* (AO3/4) - Coronavirus Translation

4.2.6A-A* (AO3/4) - Transcription

4.2.7A-A* (AO3/4) - Translation

4.3Mutations & Meiosis

4.3.1Mutations

4.3.2Meiosis

4.3.3A-A* (AO3/4) - Meiosis

4.3.4Meiosis vs Mitosis

4.3.5End of Topic Test - Mutations, Meiosis

4.3.6A-A* (AO3/4) - DNA,Genes, CellDiv & ProtSynth

4.4Genetic Diversity & Adaptation

4.4.1Genetic Diversity

4.4.2Natural Selection

4.4.3A-A* (AO3/4) - Natural Selection

4.4.4Adaptations

4.4.5Investigating Natural Selection

4.4.6End of Topic Test - Genetic Diversity & Adaptation

4.4.7A-A* (AO3/4) - Genetic Diversity & Adaptation

4.5Species & Taxonomy

4.5.1Classification

4.5.2DNA Technology

4.5.3A-A* (AO3/4) - Species & Taxonomy

4.6Biodiversity Within a Community

4.6.1Biodiversity

4.6.2Agriculture

4.6.3End of Topic Test - Species,Taxonomy& Biodiversity

4.6.4A-A* (AO3/4) - Species,Taxon&Biodiversity

4.7Investigating Diversity

4.7.1Genetic Diversity

4.7.2Quantitative Investigation

5Energy Transfers (A2 only)

6Responding to Change (A2 only)

6.1Nervous Communication

6.1.1Survival

6.1.2Plant Responses

6.1.3Animal Responses

6.1.4Reflexes

6.1.5End of Topic Test - Reflexes, Responses & Survival

6.1.6Receptors

6.1.7The Human Retina

6.1.8Control of Heart Rate

6.1.9End of Topic Test - Receptors, Retina & Heart Rate

6.2Nervous Coordination

6.2.1Neurones

6.2.2Action Potentials

6.2.3Speed of Transmission

6.2.4End of Topic Test - Neurones & Action Potentials

6.2.5Synapses

6.2.6Types of Synapse

6.2.7Medical Application

6.2.8End of Topic Test - Synapses

6.2.9A-A* (AO3/4) - Nervous Comm&Coord

6.3Muscle Contraction

6.3.1Skeletal Muscle

6.3.2Sliding Filament Theory

6.3.3Contraction

6.3.4Slow & Fast Twitch Fibres

6.3.5End of Topic Test - Muscles

6.3.6A-A* (AO3/4) - Muscle Contraction

6.4Homeostasis

6.4.1Overview of Homeostasis

6.4.2Blood Glucose Concentration

6.4.3Controlling Blood Glucose Concentration

6.4.4End of Topic Test - Blood Glucose

6.4.5Primary & Secondary Messengers

6.4.6Diabetes Mellitus

6.4.7Measuring Glucose Concentration

6.4.8Osmoregulation

6.4.9Controlling Blood Water Potential

6.4.10ADH

6.4.11End of Topic Test - Diabetes & Osmoregulation

6.4.12A-A* (AO3/4) - Homeostasis

7Genetics & Ecosystems (A2 only)

7.1Genetics

7.1.1Key Terms in Genetics

7.1.2Inheritance

7.1.3Linkage

7.1.4Multiple Alleles & Epistasis

7.1.5Chi-Squared Test

7.1.6End of Topic Test - Genetics

7.1.7A-A* (AO3/4) - Genetics

7.2Populations

7.2.1Populations

7.2.2Hardy-Weinberg Principle

7.3Evolution

7.3.1Variation

7.3.2Natural Selection & Evolution

7.3.3End of Topic Test - Populations & Evolution

7.3.4Types of Selection

7.3.5Types of Selection Summary

7.3.6Overview of Speciation

7.3.7Causes of Speciation

7.3.8Diversity

7.3.9End of Topic Test - Selection & Speciation

7.3.10A-A* (AO3/4) - Populations & Evolution

7.4Populations in Ecosystems

7.4.1Overview of Ecosystems

7.4.2Niche

7.4.3Population Size

7.4.4Investigating Population Size

7.4.5End of Topic Test - Ecosystems & Population Size

7.4.6Succession

7.4.7Conservation

7.4.8End of Topic Test - Succession & Conservation

7.4.9A-A* (AO3/4) - Ecosystems

8The Control of Gene Expression (A2 only)

8.1Mutation

8.1.1Mutations

8.1.2Effects of Mutations

8.1.3Causes of Mutations

8.2Gene Expression

8.2.1Stem Cells

8.2.2Stem Cells in Disease

8.2.3End of Topic Test - Mutation & Gene Epression

8.2.4A-A* (AO3/4) - Mutation & Stem Cells

8.2.5Regulating Transcription

8.2.6Epigenetics

8.2.7Epigenetics & Disease

8.2.8Regulating Translation

8.2.9Experimental Data

8.2.10End of Topic Test - Transcription & Translation

8.2.11Tumours

8.2.12Correlations & Causes

8.2.13Prevention & Treatment

8.2.14End of Topic Test - Cancer

8.2.15A-A* (AO3/4) - Gene Expression & Cancer

8.3Genome Projects

8.3.1Using Genome Projects

8.4Gene Technology

8.4.1Recombinant DNA

8.4.2Producing Fragments

8.4.3Amplification

8.4.4End of Topic Test - Genome Project & Amplification

8.4.5Using Recombinant DNA

8.4.6Medical Diagnosis

8.4.7Genetic Fingerprinting

8.4.8End of Topic Test - Gene Technologies

8.4.9A-A* (AO3/4) - Gene Technology

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