Download What is the structure and function of the plasma membrane?

Topic 4 learning objectives
Learning objective questions – What is the structure and function of the plasma membrane?
•
What are the principal parts of body cells?
The cytoplasm which consists of structures inside the cell, the plasma membrane which
separates the internal structures of the cell from the outside environment.
•
What is the fluid mosaic model?
Refers to the structure of the plasma membranes and the way in which the cells and
phospholipids are arranged and the plasma membrane is made up of a sea of fluid lipids.
•
What is the structure of the lipid bilayer?
The lipid bilayer composed of phospholipids which is two layers of phospholipids back to
back with the polar head at the tops and the fatty acids (non-polar ends) facing inwards to
each other.
•
What are integral proteins?
These are the proteins that are embedded within the lipid bilayer and these include
cholesterol.
•
What are peripheral proteins?
They are not as securely attached to the lipid bi layer as intergral proteins but rather they
form a relatively loose attachment with the polar heads or with the intergral proteins.
•
What are glycoproteins?
Are membrane proteins which have carbohydrate groups attached to the ends that protrude
into the extracellular fluid and these are important for immune system function and cell
adhesion.
•
What are some examples of membrane protein functions?
They facilitate ion channels or pores for ions to pass through the membrane, there are also
carrier proteins which transport specific materials across the plasma membrane, they also
act as receptors which recognise and facilitate binding of ligands to produce specific changes
within a cell and also important in enzymes which lower the activation energy of reactions.
Learning objective questions – How do cells move substances across the membrane?
•
What do permeable and impermeable mean?
Permeable refers to a structure that substances can pass through whereas impermeable is a
structure that substances cannot pass through.
•
What does the term “selectively permeable” mean?
This means that the structure may let specific substances pass through but won’t let others.
•
What types of substances is the plasma membrane permeable to?
Non polar, uncharged molecules such as oxygen, carbon dioxide and steroids
•
What types of substances is the plasma membrane impermeable to?
Ions and large uncharged molecules such as glucose.
•
What types of substances is the plasma membrane slightly permeable to?
Smaller polar molecules such as water or urea.
•
What is a concentration gradient?
Refers to the difference in concentration of a particular substance inside a cell compared to
the outside concentration of that substance.
•
What is an electrical gradient?
Results when there is a difference in charge between the inside and outside of the cell.
•
What is the difference between passive and active processes to move substances across
the membrane?
Pass processes do not require energy as they involve the movement of substances down
their concentration from a region of high concentration to low concentration whereas active
process require energy as they move substance against their concentration gradient from a
region of low concentration to high concentration.
•
What is diffusion? Explain why this occurs.
Diffusion is the net movement of a substance from an area of high concentration to an area
of low concentration and this does not require energy, thus is a passive process and this
occurs because over time the random movement of toms causes molecules to move away
from another.
•
What factors influence the rate of diffusion?
The steepness of the concentration gradient such as how big the difference is between high
and low concentrations. Also temperature as molecules/atoms move quicker during higher
temperatures thus diffusion rates are quicker. Surface area also affect the rate of diffusion
as the larger the surface area available for diffusion the faster diffusion will take place.
•
What is the difference between simple and facilitated diffusion?
Simple diffusion is where the substance is able to move freely through the membrane and
down its concentration gradient whereas facilitated diffusion involves an intergral protein to
aid the process of diffusion for substances that cannot normally pass through the
membrane.
•
What is a vesicle?
A small and spherical sac of membrane that can be used to transport or store substances.
•
What is endocytosis?
Term used to describe the movement of substances into the cell via a vesicle formed from
the plasma membrane.
•
What is exocytosis?
Term used to describe the process by which substances contained inside vesicles are
released from the cell.
Learning objective questions – Osmosis and tonicity?
•
What is osmosis?
Is the movement of water molecules through a selectively permeable membrane from areas
of low solute concentration to areas of high solute concentration.
•
What is hydrostatic pressure?
Is the pressure that is exerted by a liquid on a container such as blood exerts pressure on
walls of blood vessels.
•
What is osmotic pressure?
•
What does tonicity refer to?
Refers to the ability of a solution to change the volume of cells by altering their water content.
•
What is an isotonic solution?
Is one where cells placed into the solution maintain their volume and the concentration of
solutes inside and outside the cell is equal and there is no net movement of water across the
membrane.
•
What is a hypertonic solution?
Is one where the volume of the cells placed in the solution is reduced as the concentration
of solutes outside the cell is higher than the concentration inside and therefore water moves
out of cell causing it to shrink.
•
What is a hypotonic solution?
Water moves into the cell because of osmosis and this can cause the cell to burst which is
called lysis. The bursting of red blood cells is called heamolysis.
Learning objective questions – The components of body cells
•
What are the two main components of the cytoplasm?
This includes the cytosol and the organelles.
•
What is the function of ribosomes?
The ribosomes are where protein synthesis occurs.
•
Where are ribosomes found?
They can be attached to the nuclear membrane or attached to the endoplasmic reticulum
making it rough or free floating in the cytoplasm or in the mitochondria.
•
What is the endoplasmic reticulum?
A network of membranes forming flattened sacs.
•
What are the two forms of the endoplasmic reticulum? How do they differ from each
other? What functions do they perform?
The two forms include the smooth endoplasmic reticulum and the rough endoplasmic
reticulum. The smooth ER does not contain ribosome’s and is involved with the synthesis of
fatty acids and steroids. Whereas the rough ER is studded with ribosomes and involved with
protein synthesis and in muscle it stores and releases calcium ions needed for muscle fibre
contraction.
•
What is the structure and function of the golgi complex?
The golgi complex is composed of flattened membrane sacs called cisternae and it modifies,
sorts and packages and transports proteins received through the rough ER.
•
What is the structure and function of lysosomes?
Lysosomes are vesicles of membrane produced by the golgi complex that contain digestive
enzymes which break down debris or unwanted materials in cells.
•
What is the structure and function of mitochondria?
The mitochondria consists of two membranes the inner and outer and the inner membrane
is highly folded into structures called cristae which increases the surface area for more area
available for chemical reactions to take place.
•
What is the structure of the nucleus?
The nucleus is a spherical shaped structure located within the cytoplasm and it is
surrounded by a double membrane called the nuclear envelope that separates the contents
of the nucleus from the rest of the cell.
•
Where are nucleoli found and what is their function?
Or nuceluous are invoved with the production of ribosome subunits that will join together in
the cytoplasm to from functioning ribosomes.
•
What is the primary function of the nucleus?
Storage of genetic info, regulation of protein production by cell.
•
How is genetic material arranged within the nucleus?
Genes are arranged along chromosomes which are long strands of DNA that are coiled
together.
•
What is a chromosome?
Long strands of DNA that are highly coiled and held together by proteins called histones.
•
What is chromatin?
The complex of DNA, proteins and some RNA.
•
What are the two main processes involved in the conversion of a gene into a protein?
Briefly, explain how these two processes occur.
Transcirption and translation. During transcription the DNA sequence of a gene is converted
into a sequence of RNA in the form of messenger RNA and this mRNA exits the nucleus and
enters the cytosol where it binds to a ribosome and this is where translation occurs. During
translation the mRNA sequence is read and translated into an amino acid sequence by a
ribosome. The ribosome moves down the mRNA molecule and reads the sequence of
nucleotides and adds the correct amino acids to the growing protein and the translation of
mRNA ends when a STOP mRNA sequence is reached (UGA) At this point the protein
detaches from the ribosome.
Learning objective questions – How do cells divide?
•
What is a somatic cell?
Is any body cell other than a gamete (sperm or oocyte.)
•
What are the two processes that occur during somatic cell division? What is the result of
these processes?
•
What are the four phases of mitosis?
Prophase where chromatin condenses into chromatids that can be seen under light
microscope. Metaphase where chromatids are lined up the middle of the cell and Anaphase
where the chromatids split into two halves and these halves are then pulled to the opposite
ends of the cell and anaphase where chromosomes uncoil back into threads of chromatin.
•
What occurs during cytokinesis?
The cells plasma membrane is constructed until the cell is sliced in half to produce two new cells
and the organelles are divided equally into the two cells.
Learning objective questions – Epithelial tissue
•
What is a tissue?
A group of similar cells that function together and carry out specialized activies.
•
What are the four basic types of tissue in the body?
Epithelial tissue, connective tissue, muscle tissue and nervous tissue.
•
What is epithelial tissue?
Epithelial tissue covers the whole surface of the body. It is made up of cells closely packed
and ranged in one or more layers.
•
What makes epithelial tissue an excellent protective barrier?
The fact that it covers the whole surface of the body and therefore is a protective barrier for
body surfaces and provides a way of separating and isolating substances within the body.
•
What are the three surfaces of epithelial cells?
These include the apical surface which faces the body surface, body cavity or lumen of a
hollow organ or duct and may also contain cilia or microvilli. The lateral surfaces face the
lateral surface of adjacent cells and often contain cell junction that bind the cells together
and the third layer is the basal surface which is located opposite the apical surface.
What is the structure of the basement membrane? What is its function?
The basement membrane usually consists of two layers which include:
-The basal lamina- is secreted by epithelial cells and is found closest to them and the lamina densa
which is found below the basal lamina and is composed of fibrous proteins produced by underlying
connective tissue. Its function is as a point of attachment and support for the overlying epithelial
tissue.
•
What are the two main divisions of epithelial tissue?
-Covering and lining epithelia:
-forms the outer covering of skin and some organs
-lines the inside of blood vessels, ducts and body cavities
- lines the inferior of the respiratory, digestive, urinary and reproductive system.
Glandular epithelia
-Forms the secreting portion of glands such as thyroid glands and sweat glands.
•
How can covering and lining epithelial tissue be classified based on the arrangement of the
cells? What is the difference between simple, stratified and pseudostratified epithelia?
Covering and lining epithelia can be classified based on two characteristics:
-
•
The arrangement of the cells into layers: can be simple (single layer) stratified (2 or more
layers) or pseudostratfied (only appears stratified but is actually a single layer)
How can covering and lining epithelial tissue be classified based on the shape of the cells?
What is the difference between squamous, cuboidal and columnar epithelial cells?
Ciliated simple columnar epithelia: a single layer of colun like cells that have cilia on their
apial surface. Stratified squamous epithelia: multiple layers of flat cells,
•
What is the function of glandular epithelial cells?
Is secretion and to help form glands in the body.
•
What are glands?
May be single or a group of glandular epithelial cells that secrete substances into ducts, onto
a surface or into the blood stream, and they can be endocrine or exocrine glands.
•
What do endocrine glands do?
An endocrine gland secretes substances into the bloodstream in the form of hormones.
•
What do exocrine glands do?
Exocrine glands secrete substances into a duct that empties on the surface of a covering and
lining epithelium such as skin surface or gastrointestinal tract.
Learning objective questions – Connective tissue
•
What are the two basic elements of connective tissue?
Extracellular matrix and cells.
•
What are the components of the extracellular matrix?
Ground substance which is found between cells that make up connective tissue it can be
gelatinous, fluid, semi-fluid or calcified. The ground substance supports cells, binds them
together, stores water and provides a medium through which substances are exchanged.
•
What are the three types fibres that can be present in connective tissue? What are the
physical properties of these fibres?
Collagen fibres: very strong fibres that resist pulling forces and they are not stiff so they still
allow the tissue to be flexible. Elastic fibres contain the protein elsatin that allow for stretch
and therefore they can return to their original shape after being stretched. Reticular fibres
are much thinner than collagen fibres and form branched networks and they provide
strength and support.
•
What are the cell types that can be present in connective tissue?
These include fibroblasts which secrete fibres and ground substance. Macrophages which
are immune cells that engulf bacteria and cellular debris, plasma cells secrete antibodies to
attack foreign substances in the body, mast cells which produce the chemical histamine
which forms part of the inflammatory response, adipocytes which store triglycerides and
white blood cells which are responsible for mediating the bodies response to infection.
•
What are the immature cell types found within loose and dense connective tissue;
cartilage; and osseous tissue? What are these cells capable of doing?
In loose and dense connective tissue the immature cells are called fibroblasts, in cartilage
they are called chondroblasts and osteoblasts in osseous tissue. These cell types have the
capacity to replicate via mitosis and also secrete extracellular matrix.
•
What are the five types of mature connective tissue?
Loose connective tissue, dense connective tissue, cartilage, osseous tissue and liquid
connective tissue (blood and lymph)
•
What is the structure of loose connective tissue? What types of loose connective tissue
are there in the body?
Loose connective tissue possess fibres that are loosely intertwined and there are also many
cells present between the fibres. The types of loose connective tissue in the body include
areolar connective tissue, reticular connective tissue and adipose tissue.
•
What is the structure of dense connective tissue? What types of dense connective tissue
are there in the body?
Dense connective tissue contains more fibres but fewer cells than loose connective tissue
and the types found in the body include dense regular connective tissue, dense irregular
connective tissue and elastic connective tissue.
•
What is the structure of cartilage? What types of cartilage are there in the body?
Cartilage consists of a dense network of collagen and elastic fibres which gives cartilage its
strength and the three types of cartilage include hyaline cartilage, fibrocartilage and elastic
cartilage.
•
What is the structure of liquid connective tissue? What types of liquid connective tissue
are there in the body?
Liquid connective tissue consists of cells suspended in an extracellular matrix that is liquid
and the two types include blood and lymph.