Biology of Hair Structure and Proteins

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Questions and Answers

What is the role of sulfur-containing proteins in hair?

They serve as a lubricant for hair growth.

They render hair resistant to mechanical damage and chemical degradation. (correct)

They are responsible for hair's hydration and moisture retention.

They provide color to the hair.

Which components are present in the intercellular spaces of hair?

Sugars and fibers.

Water and carbohydrates.

Vitamins and minerals.

Lipids. (correct)

How are amino acids in hair structured compared to those in other living tissues?

They have a unique bonding arrangement exclusive to hair.

They are organized differently than in other living tissues. (correct)

They contain additional molecular layers.

They are the same as in other living tissues, without any specific organization.

What is a key characteristic of the proteins found in hair?

They have a unique backbone structure. Signup and view all the answers

What is the primary composition of hair?

Proteins and lipids. Signup and view all the answers

What is the main role of the ratio and distribution of cortex cells in human hair?

To influence hair shape formation Signup and view all the answers

Which type of cortical cells contains more matrix and is located on the outside of the hair crimp?

Orthocortex cells Signup and view all the answers

What is the average diameter and length of cortical cells in human hair?

3 µm in diameter and 5-100 µm in length Signup and view all the answers

How many layers do cuticle cells typically consist of in the hair shaft?

5-10 layers Signup and view all the answers

What shape are the cuticle cells in the structure of the hair?

Square Signup and view all the answers

What is the primary function of melanin in hair?

Providing UV protection Signup and view all the answers

What happens if mechanical stress continues to affect the cell membrane complex (CMC) in hair?

Cracks develop leading to fiber breakage Signup and view all the answers

In what way does water function concerning hair proteins?

It acts as a plasticiser and reduces rigidity Signup and view all the answers

How much water does hair typically contain in low humidity conditions (up to 60%)?

10% Signup and view all the answers

Which component is NOT part of the cell membrane complex (CMC) in hair?

Hydrophobic proteins Signup and view all the answers

What is the role of hydrogen bonds in the structure of hair?

They impact the shape and elasticity of hair due to their high number. Signup and view all the answers

Which structural component primarily accounts for the tensile strength of hair?

Intermediate Filaments (IFs) Signup and view all the answers

What characterizes the structure of keratin-associated proteins (KAPs)?

They contain high levels of sulfur-containing amino acids. Signup and view all the answers

What is the importance of the coiled-coil structure in hair?

It forms dimers that contribute to the overall stability of hair. Signup and view all the answers

How much can hair stretch before breaking?

5-10% Signup and view all the answers

Which type of bonds are primarily responsible for the cross-linking of KAPs and IFs?

S-S bonds Signup and view all the answers

What is the diameter of the complex groups formed by 32 strands of IFs?

10 nm Signup and view all the answers

What type of mechanical properties does hair possess due to its structure?

High tensile strength and significant elasticity. Signup and view all the answers

Which factor mainly affects hair manageability?

Hair shape Signup and view all the answers

What happens to Caucasian hair fibers as they age?

They become finer Signup and view all the answers

In terms of hair assembly properties, which of the following is NOT affected by hair shape?

Hair color Signup and view all the answers

What primarily contributes to increased knotting in curly hair?

Increased contact points Signup and view all the answers

What happens in the post-yield region during the tensile deformation of hair fibers?

Disulphide bonds break Signup and view all the answers

Why do straight and circular hair shapes exhibit higher manageability?

Better fiber alignment Signup and view all the answers

What effect does a highly elliptical hair shape have on mechanical stress distribution?

It leads to uneven stress distribution Signup and view all the answers

Which trait of Caucasian hair shows high variability?

Hair size and color Signup and view all the answers

What is a characteristic of hair when it is wet in terms of manageability?

It requires more force to comb Signup and view all the answers

Which of the following factors contributes to the structural damage in curly hair?

Complex knotting leading to stress Signup and view all the answers

What two types of melanin are produced during melanogenesis?

Eumelanin and Pheomelanin Signup and view all the answers

Which hair type has the largest cross-sectional area?

Asian Signup and view all the answers

How is hair ellipticity defined?

The ratio between the longer and shorter diameters Signup and view all the answers

What characteristic of hair affects its mechanical properties?

Cross-sectional area and ellipticity Signup and view all the answers

Which hair type tends to tangle more due to its shape?

African hair Signup and view all the answers

In terms of strength, what factor does the cross-sectional area of hair reflect?

How thick the hair fibre is Signup and view all the answers

What measurement is provided alongside the cross-sectional area for Caucasian hair?

Standard deviation Signup and view all the answers

How does the presence of eumelanin affect hair color?

Produces a dark brown or black color Signup and view all the answers

Study Notes

Hair Structure and Morphology Revisited

This presentation covers the structure and morphology of hair.
It discusses hair chemistry, fibre morphology, cuticle and cortex structures.
It explores the scientific knowledge of different hair types and approaches to product formulation.

Lecture Plan

Hair chemistry and hair fibre morphology
Hair cuticle and cortex structures
Current scientific knowledge of different hair types
Approaches to product formulation for diverse consumer needs

Hair Chemical Composition

Hair is primarily composed of protein (91%).
Lipids are present in intercellular spaces.
Sugars and protein-bound sulfur are also components.
Sulfur-containing proteins make hair resistant to damage.
Zinc is present at 200 ppm.

Hair Chemical Composition: Proteins

Proteins are made up of amino acids.
Amino acids are linked by peptide bonds.
Hair proteins have specific amino acid compositions.
Differences in amino acid sequences and structure distinguish hair from other body proteins.

The Amino Acids (AAs) of Hair

Identical amino acids compose hair as other organic tissues, but their organization varies.
The presentation identifies a range of amino acid types and their functions. Key examples include polar, non-polar, and charged side chains, categorized as acidic or basic.
Data on specific amino acids and hair types are listed.

Hair Proteins: Primary Structure

The percentage of different amino acids in hair is presented in a table.
Cystine is the highest and most relevant component related to sulfur bonding and strength.
Polar acidic amino acids are higher than others and important for water absorption and retention by the hair fibre.
Amino acid residues are influenced by grooming techniques and chemical treatments.
Differences are determined by various acidic and basic amino acids with a higher percentage than basic ones.

Hair Proteins: Secondary Structure

Hair proteins fold into specific shapes like alpha helix and beta pleated sheets.
Hydrogen bonds (and other bonds) are key to stabilising these structures.
These structures enable hair to maintain its shape and elasticity.
Hydrophilic groups in the amino acid residues attract and bind water.
Water is crucial for maintaining the protein's 3D structure.

Secondary Structure Bonds

Hydrogen bonds
Salt bridges (electrostatic bonds)
Chemical bonds (disulfide and isodipeptide)
Hydrophobic interactions
Intermolecular forces
Intramolecular forces

Disulfide Bond

Thiol groups oxidise to form disulfide bridges.
The disulfide bridge formation occurs within the follicle.
These bonds are vital for stabilizing protein structures and hair shape.
Chemical treatments and UV radiation can break disulfide bonds.

Hair Structure: Crystalline Regions

A significant portion of hair is composed of alpha-helical structures.
Hydrogen bonds stabilize the alpha-helices.
Hydrogen bonds between carbonyl oxygen and amino hydrogen residues are crucial.
Weak hydrogen bonds have a large impact due to their high number within the structures.

Crystalline Hair Protein Structure

Two coils of hair proteins forming a dimer.
Intermolecular forces between aliphatic groups and electrostatic attraction hold the coils together.
The crystalline structure is hydrophobic.

Hair Structure: Crystalline Regions- IFs

Coiled coils form dimers and are packed tightly into more complex groups of 32 strands.
These structures (IFs) form small building blocks.
The structure (approximate diameter: 10nm) provides hair with tensile strength and stretch ability before breakage.

Hair Structure: Amorphous Matrix (KAPs)

IFs are embedded in a matrix of KAPs.
KAPs are amorphous, globular with beta-sheet segments.
KAP structures contain a high level of sulfur-containing amino acids (like cysteine).
KAPs cross-link with IF proteins, supporting hair elasticity (stretch ability to about 5-10%).

Hair Fibre Shaft: Structural Schematics.

Schematic diagrams showing the relationship between amino acids, keratin proteins, tetramers, intermediate filaments (IFs), microfibrils, and macrofibrils.

Hair Cuticle and Cortex Structures (Lecture Plan)

Presentations on the structure and function of the cuticle and cortex.

AFM Imaging of Hair Structure

Presentations of atomic force microscopy (AFM) images of different layers and parts of hair structure. Includes Endocuticle, Exocuticle, Cortex, and sections of the cell membrane complex.

Hair Structure (Cortical Cells)

Two main types of cortical cells (ortho and para-cortex) exist.
Their arrangement in the hair shaft plays a role in crimp and shape.

Cortex

Innermost and largest structural element in the hair fibre.
The cortex is comprised of spindle-shaped, oriented cells.
Cells have a rod-shaped configuration called macrofibrils.
The macrofibrils are complex structures and contain melanin.

Cuticle

Outer structure of the hair shaft.
Composed of 5-10 overlapping, flat cuticle cells.
Cells have square shapes with similar side lengths.
Inner ends (proximal) are covalently bonded to the cortex.

Cuticle Cell Structure

A-layer & Exocuticle: High cysteine content, forming a tough, resilient barrier.
Endocuticle: Lower cysteine content, mechanically weak, and swellable.

Cuticle Structure Summary

Cuticle structure and properties are related to human hair characteristics, including resilience to external impacts and uptake (or rejection) of water.
The different layers within the cuticle affect hair shine, friction coefficient, and water absorption properties and thus influences product choices.

External Tear and Wear of Fine Straight Fibre Examples

Microscopic images showing damage to the cuticle cells.
Damage is correlated to chemical treatments and common washing/styling processes.

Cell Membrane Complex (CMC)

Contains a large portion of hair's fatty acids.
Contains 18-methyl eicosanoic acid, ceramides, and cholesterol.
The CMC is found within cuticle, cortex, and between these regions.
Cell membrane pathways are frequently used for active ingredients.

Cell Membrane Complex - cont

CMC contains bound and free fatty acids.
Components such as Cholesterol, sulfates, and ceramides form the ẞ-layers.
The CMC is frequently affected and damaged by mechanical and chemical stresses.
Difference in content for the layers within the complex is visible.

Water

Water binds to hydrophilic amino acids.
Tightly bound water remains after drying.
Additional water binds to the first layer.
Water is found in KAPs, while IFs are hydrophobic.
Water acts as a plasticiser, reducing hair rigidity.

Melanin

Melanin's function is to create UV protection in hair. Different forms of melanin contribute to unique hair colour and shade.
Tyrosine is the initial amino acid.
Dopaquinone and Cysteine are important in the process.
Two types of melanin are discussed: eumelanin and pheomelanin.

Hair Fibres Cross Sectional Images: Melanin Distribution

Presentation of images demonstrating melanin distribution.

Current Scientific Knowledge of Different Hair Types

Presents current scientific knowledge of differences among hair types and examples of these differences.
The knowledge includes descriptions of different hair types based on morphology, structure, and cross-sectional area.

Some Defined Differences

Physical aspects differ among hair types: cross-sectional area, ellipticity, overall shape, and mechanical properties.
Tables present data categorized by hair type (e.g., Asian, Caucasian, African American).

Cross Sectional Area CSA

Cross-sectional area reflects hair thickness and strength.
African hair has the largest cross-section area, followed by Asian and Caucasian.

Cuticle Differences

Hair follicle shape related to differences in hair shape, such as African, Caucasian, and Asian.
Microscope images display differences.

Cuticle Differences cont

Shine differences among hair types (with Asian hair being shiniest).
Cuticle spacing varies among hair types with African hair having the widest spacing and Asian hair the narrowest.

Hair Assembly Properties

Hair density, colour, shape, and growth rate are related to assembly aspects.

Global Hair Shape Classification

A classification system for hair shapes based on curl patterns (I to VIII).
It's related to manageability of the hair and its integrity/quality.

Caucasian Hair Specific Data

Data analysis shows variability among Caucasian hair types regarding size and shape with age.

SEM Images of Highly Elliptical and Curly Hair

SEM images of highly elliptical and curly hair.

Hair Knots and Breakage - The Effect of Shape

Relationship between hair shape and knotting/breakage.
Differences related to shape are visualized from images.

The Tensile Curve (Tensile Deformation of the Hair Fibre).

Graph showing the relationship between force and strain in hair during deformation.
Indicates regions of elasticity, yield, and breakage in hair fibers.

Hair Manageability

Straight hair is more manageable, while curly hair is more difficult.
Factors like fibre alignment, friction, and stress distribution across the fibres contribute to manageability.

Approaches to Product Formulation for Diverse Consumer Needs

The importance of formulating products with diversity in mind
The presentation notes that approaches to product formulations should consider differences among consumer groups

Diverse Consumer Needs

Examples of diverse consumer needs related to hair care.
A diversity of hairstyles, preferences and requirements across consumers are noted.

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Description

Explore the fascinating role of sulfur-containing proteins and the composition of hair in this quiz. Test your understanding of the unique structural features and functions of hair proteins, amino acids, and the importance of melanin. Learn about the various layers and types of cells that contribute to the characteristics of human hair.