Chapter 2 - Cells that make up a Human

Cell membrane

• Outer membrane of cell

• Double layer of lipid molecules and associated proteins

• Controls movement of substances in and out of the cell

• Encloses content of the cell

• Separates the cell contents from the environment outside and from neighbouring cells

Cytoplasm

Jelly like or watery material that fills up space between nucleus and cell membrane
Cytosol: liquid part of cytoplasm (75-90% water)

• Metabolic reactions occur here

• Plays a role in controlling osmotic pressure and flow of chemicals in and out of cell

Organelles: specialised structures suspended in cytoplasm

Nuclear membrane

• A double membrane with space in between the 2 membranes

• Separates nucleus from cytoplasm

Nuclear pores

• gaps in nuclear membrane

• allows large molecules such as messenger RNA to enter and leave nucleus

Genetic material

• DNA in the form of chromatin when cell is not dividing

• DNA determines the type of proteins cell can make

Nucleolus

• Contains RNA

• Plays a part in protein synthesis

Nucleoplasm

Jelly-like, nucleolus and DNA suspended in it

Ribosomes

• very small, cell containing thousands

• found on membranes or floating freely

• amino acids are joined to make proteins at the ribosome

Endoplasmic Reticulum

• Smooth/ agranular ER: lack ribosomes

• Rough/ granular ER: ribosomes embedded in surface

• Channels move and store materials around in cell

• Membranes provide surface for chemical reactions

Golgi Apparatus

• Flattened membranes stacked upon each other (Near nucleus)

• Modify and package proteins for secretion from cell

• Move materials from ER to the edge of membrane to form small bubbles of liquids surrounded by a membrane (vesicle) containing proteins

Lysosomes

• Formed from the golgi body (cell breaks down if lysosomes break down)

• Contains enzymes to digest proteins, fats, nucleic acids and carbohydrates and also worn out organelles

Mitochondria

• Outer membrane is smooth, inner membrane has cristae (folds) which increase SA

• Produces energy through chemical reaction of cellular respiration (breaking down fats and carbohydrates)

• Control level of water and other materials in cell

Cilia & Flagella

Cilia: short, numerous (cells lining trachea)

Flagella: longer (only in human sperm cells)

Cytoskeleton

• A framework of protein fibres

• Gives cell its shape and assists in cell movement

• Microtubules: hollow rods, keep organelles in place or move around in cytoplasm

• Microfilaments: protein filaments, move materials around the cytoplasm or move whole cell

Inclusions

Chemical substance found in cytoplasm of the cell (haemoglobin in RBC)

Tissue fluid/ extracellular fluid

fluid surrounding the cell

Homeostasis

Maintenance of a constant internal environment despite fluctuations in the external environment

Fluid Mosaic Model

Fluid - most protein and phospholipid molecules can move laterally
Mosaic - proteins and other molecules are embedded in a framework of phospholipids.

Phospholipid bilayer

made up of 2 layers of lipid molecules which contain a phosphate group

Amphipathic

having both hydrophilic head and hydrophobic tails

Cholesterol

Important for the function integrity and stability of membrane

Integral/ Peripheral proteins

Integral - that span the whole membrane

Peripheral - are on one side or the other of the membrane

Which structures can be embedded in the phospholipids?

Proteins, Carbohydrates & Cholesterol

Channel proteins

• Form small openings for molecules to diffuse through

• Allows transport of specific substances across a cell membrane

Carrier proteins

• Binding site on protein surface “grabs” certain molecules and pulls them through the cell

• Help specific molecules or ions pass through the cell membrane

Receptor proteins

• Where hormones and neurotransmitters and other chemicals attach to the surface of the cell

• Substance impacts on the contents inside

Cell recognition proteins (cell identity markers)

ID tags, to identify cells to the body’s immune system

(FotM) Acts as a physical barrier

Separates the cell cytoplasm from the extracellular fluid around the cell. This is important because their composition are very different

(FotM) Regulates passage of materials

Controls the movement of materials in and out of the cell

(FotM) Sensitive to changes

Affected by changes in the extracellular fluid. It has receptors that are sensitive to particular molecules

(FotM) Helps support the cell

The internal part of the membrane is attached to microfilaments of the cell’s cytoskeleton, thus giving support to the whole cell

Transport Mechanisms

Active processes: requires energy
Passive processes: does not require energy

Diffusion

Passive movement of molecules from a higher to lower concentration (until equilibrium is reached) eg, gas exchange in lungs

Osmosis (diff)

The diffusion of water/solvent across a semi-permeable membrane due to concentration differences

Tonicity (diff)

• Refers the concentration of solutes

• Is a relative term, comparing 2 different solutions

Hypertonic (Tonicity)

• A solution with a greater solute concentration compared to another solution

• Inside the cell to outside

• Water leaves cell, which shrivels (crenation)

Hypotonic (Tonicity)

• A solution with a lower solute concentration compared to another solution

• Outside to inside the cell

• Water enters the cell, which may burst (Lysis)

Isotonic (Tonicity)

• A solution with an equal solute concentration compared to another solution

• No net movement of water

Carrier Mediated Transport

• Proteins in the membrane bind to molecules to be transported

  Important Characteristics:

• Carrier proteins are specific

• Carriers can become saturated

• Carrier activity is regulated by substances, eg. hormones

Facilitated Diffusion (CMT)

Process of passive transport of molecules or ions across a biological membrane via a specific integral protein along the concentration gradient (high to low concentration)

Active Transport (CMT)

Requires energy because the substance are transported against the concentration gradient (low to high concentration)

Vesicular transport

Movement of substances across the cell membrane in membrane bags called vesicles

Exocytosis (VT)

Contents move inside to outside

Endocytosis (VT)

Contents move inside to outside

• Phagocytosis: “Cell eating” (Solids being transported)

• Pinocytosis: “Cell drinking” (Fluids being transported)

• Receptor-mediated endocytosis: specific particles, recognition

Tissue

A group of cells that are similar in structure and that work together to carry out a particular task

Epithelial Tissue

Is a covering or lining tissue

Epithelial tissue function

• Protects us from outside world - skin

• Absorbs - stomach and intestinal lining - gut

• Filters - kidney

• Secretes - glands

Epithelial tissue characteristics

• Cells close together forming a protective barrier

• Has 1 free (apical) surface open to outside of body or inside (cavity) an internal organ

• Has on fixed (basal) section attached to underlying connective tissue

• No blood vessels, but soak up nutrients from blood vessels in the connective tissue underneath

• Have a lot of nerves (innervated)

• Very good at regenerating

Connective tissue function

• Holds all body parts together

• Provides, support, protection, framework, fills space, stores fat and produces blood cells and fight infection

Connective tissue characteristics

• Most abundant tissue in body

• Includes bone, cartilage, tendons, ligaments and fat storage tissue

• Composed of more scattered cells with intercellular matrix

• Have good blood supply

Loose Connective Tissue

• Space between muscles throughout body

• Binds to skin to underlying organs & organs to organs

Adipose tissue

• Beneath skin, around kidney and eyeballs, abdominal membranes

• Protective cushion, insulation to preserve body heat, stores energy

Blood tissue

Circulates throughout the body

Fibrous Connective tissue

• Dense tissue, closely packed, thick collagenous fibres and fine network of elastic fibres. Few cells, poor blood supply thus slow heating

• Tendons: connect muscles to bone

• Ligaments: connect bones to bones

Cartilage

all cartilage cells are called chondrocytes

Bone tissue

Osseus tissue, rigid due to mineral salt

Muscle tissue characteristics

• Cells are long & thin and often called muscle fibres

• Respond to stimulus by contracting and becoming shorter

Skeletal muscle tissue

• Structure: attached to bones - voluntary (striated)

• Location: limbs, tongue, face

• Working: contract quickly but can’t remain contracted for long, so get fatigued

Smooth muscle tissue

• Structure: in hollow organs such as walls of stomach, intestine and uterus - involuntary (no striations

• Working: contracted slowly but can remain contracted for long, so don’t get fatigued

Cardiac muscle tissue

• Structure: wall of the heart - involuntary (have striations)

• Working: contract quickly and rhythmically. Therefore, do not get fatigued

Nerve tissue

• Made up of specialised nerve cells called neurons

• Neurons easily stimulated and transmit impulses rapidly

• A nerve made up of many nerve cell fibres (neurons) bound together by CT

• React to stimuli and conduct impulses to various organ in the body which bring about a response to the stimulus