cells: topic 2

Why do you need thin sections of a specimen when using a light microscope?

So that light can pass through

Why do you stain some specimens?

Most structures are not coloured and require staining to be made visible

What is a micrograph?

A light micrograph is a photograph of an image taken through a light microscope

Why would a light micrograph include a scale bar or image magnification?

So you can calculate three actual size of the specimen

Name 4 advantages of a light microscope

• cheap, easy to use and portable

• Natural colour is maintained

• Samples are easy to prepare

• Specimens may be living or dead

Name the 2 types of microscope

• transmission electron microscope (TEM)

• Scanning electron microscope (SEM)

Explicable how a Transmission electron microscope works

• a beam of electrons is passed through the specimen and focused to produce an image

• The wavelength of electrons is shorter than visible light

How large can the magnification of a TEM be

X500000 (much greater than light microscopes)

Negatives of a TEM

• very thin sections

• A vacuum so can only view dead cells

• Specimen must be stained with heavy metal compounds

• Sample preparations require great skill and may introduce artefacts

• Expensive

Explain resolution

• the ability to distinguish between 2 separate points and depends upon the wavelength used

Units

1 meter= 1m=1m=1m in a meter

1 centimetre=1cm=0.01m=100cm in a meter

1 millimetre=1mm=0.001m=1000mm in 1m

1 micrometer=1um=0.000001m=1000000um in 1m

1 nanometer=1nm=0.000000001m=1000000000 in 1m

Describe the structure of the nucleus

• consisting of a nuclear envelope (a double membrane) with nuclear pores

• Nuclear envelope is attached to RER

• Contains the genetic material and nucleolus

Describe the function of the nucleus

• allows mRNA to travel to the cytoplasm through nuclear pores

• The nucleolus manufactures rRNA and assembles the ribosomes

Descirbe the structure of the rough endoplasmic reticulum

• sacs made of membrane called cisternae

• Covered in ribosomes, the sites of protein synthesis

Descirbe the functions of the rough endoplasmic reticulum

The site of aerobic respiration (ATP production)

Describe the structure of the smooth endoplasmic reticulum

• Sacs of membrane called cisternae which is not covered in ribosomes

• Has a smooth appearance

Describe the function of the smooth endoplasmic reticulum

Synthesises, stores and transports lipids and carbohydrates

Describe the structure of the Golgi body

• similar to SER

• Forms Golgi vesicles

Describe be the function of the Golgi body

• modification and packaging of proteins:

— adding carbohydrate of proteins to from glycoproteins

— producing secretory vesicles

— secrete carbohydrates

— transports, modify and stores lipids

— forms lysosomes

Describe the structure of the mitochondria

• double membrane, the inner membrane is highly folded to form cristal

• The fluid inside is called the matrix

• Contains a small amount of mitochondrial DNA and small ribosomes

• They are self-replicating

Describe the function of mitochondria

The site of aerobic respiration (ATP production)

Describe the structure of lysosomes

• formed from vesicles produced by the Golgi

• Contains hydrolytic enzymes

Describe the function of lysosomes

• hydrolysing cells and organelles

• Exocytosis to release enzymes outside of the cell

Describe the structure of ribosomes

• 80S are found in eukaryotic cells

• 70S are found in prokaryotic cells, mitochondria and chloroplasts

• Consists of 2 subunits, 1 large and 1 small

• Made from ribosomal RNA (rRNA) and protein

Describe the function of ribosomes

The site of protein synthesis

Describe the structure of chloroplasts

• consists of a double membrane and a fluid filled centre called the stroma

• Flattered sacs of membranes, called thylakoids, stacked to form grana

• Chlorophyll is found inside the thylakoids

• Contains a small amount of DNA, small ribosomes (70S) and starch grains

• They are self replicating

Describe the function of chloroplasts

Absorbs light for photosynthesis

Describe the structure of the cell wall

• foun din plant, algal and fungal cells

• Found outside of the cell surface membrane

• Cellulose in plant ells

• Chitin in fungal cells

Describe the function of the cell wall

• supports the cell and plants as a whole

• Withstanding osmotic pressure

What is cell specialisation?

Cells become specialised to perform a particular role

Name 3 different ways cells specialise

• organelles contents

• Shape

• Proteins produced

What is cellular organisation?

Multicellular organisms can be organised into 4 different sections

What are the 4 stages of cellular organisation?

• cells

• Tissues

• Organs

• Organ systems

What is a cell?

The basic unit of structure and function in living organisms

What is a tissue?

A collection of similar cells that perform a specific function

What is an organ?

Different tissues that work together to perform a function

What is an organ system?

Portman’s that work together to perform particular functions

Why might a cell have lots of mitochondria?

For high requirements of energy e.g muscle cells

Why might a cell have lots of RER?

for production of proteins e.g liver cells produce lots of enzymes

Why might a cell have lots of lysosomes?

For production of hydrolytic enzymes e.g phagocytic white blood cells

Why would an organelle have a flagellum?

For movement/propulsion e.g sperm cells

Why would an organelle have microvilli?

To increase surface area for absorption e.g epithelial cells of the small intestine

Why would an organelle have cilia?

To aid movement of something outside the cell e.g ciliated epithelial lining the trachea moves mucus away from the lungs

Why would a cell be very thin?

For a short diffusion distance e.g capillaries

Why would a cell be very long and thin?

To cover larger distances e.g speed up impulses in neurones (nerve cells)

Why would a cell be very large?

To provide energy stores (yolk in egg cells)

Why would a cell (red blood cells) be in the shape of a bacon cave disc?

It increases effectiveness of diffusion of oxygen into cells

Viral replication: stock response

• viruses bind to receptors on the host cell with their attachment proteins

• They inject their nuclei acid into the host cell

• The host cell produces the viral components (nuclei acid, enzymes and structural proteins)

• These then assemble into new viruses and usually burst out of the cell to infect other cells

Describe the process of binary fission

1. Cell replicates its DNA

2. The cytoplasmic membrane elongates, separating DNA molecule

3. Cross wall forms; membrane invaginate

4. Cross wall forms completely

5. Daughter cells

Explain water potential

Water molecules move around and collide with the cell membrane. This creates pressure wich is the water potential.

What is osmosis?

The net movement of water molecules from an area of higher water potential to an area of lower water potential though a partially permeable membrane.

Explain solute potential

Solutes resist the movement of water molecules. This lowers the water potential of a solution by an amount know as the solute potential. Solutions have a negative water potential

Explain pressure potential

The positive contribution made up by pressure to water potential wich raises the water potential making it become less negative and is important in plant cells

Explain incipient plasmolysis

When the protoplasm begins to pull away from the cell wall so is no longer pressing on the cell wall

What basic structure do all membranes have?

A plasma membrane

What are eukaryotic cells surrounded by?

Plasma membrane

What is plasma membrane permeability?

Water soluble molecules cannot diffuse across but lipid soluble molecules can diffuse through the belayer

What is an exception to plasma membrane permeability?

• small molecules such as water and carbon dioxide can fit between the phospholipids and therefore can diffuse through the bilayer

• However although ions are small they are charges so are repelled by the membrane so cannot diffuse

What is the function of channel and carrier proteins?

• channel proteins allow transport of water soluble substances

• Carrier proteins allow active transport

What are proteins role in membranes?

• provide structural support

• Channel/carrier proteins

• Form cell surface receptors for cell recognition

• Adhesion of cells

• Receptor sites

What is cholesterols role in membranes?

• reduce lateral movement, providing strength and stability

• Reduce fluidity at high temperatures

• Prevents leakage of water and dissolved ions from the cell

What is the role of glycolipids and glycoproteins in membranes?

• act as recognition sites

• Maintain stability of membrane

• Helps cells attach to form tissues

• Glycoproteins specifically form receptors for hormones and neurotransmitters

Why is mosiac model considered fluid?

Phospholipids can move laterally relative to open another, membrane is flexible and constantly changes shape

Where does mosiac come from in the name of the fluid mosaic model?

Protium’s embedded in phospholipid layer vary in size, shape and pattern

Explain the partial permeability of the fluid mosaic model

• the cell surface membrane controls the movement of substances into and out of the cell

• Membranes in organelles also control entry into and exit from the organelle

Name the bodies barriers to infection

• lysozyme in tears and other secretions

• Removal of particles by cilia in nasopharyx

• Skin surface (physical barrier)

• Fatty acids

• Normal flora

• Mucus lining trachea

• Stomach (pH 2)

• Change in pH leaving the stomach

• Flushing of urinary tract

What is an antigen?

Any part of an organism or substance that is recognised as foreign by the immune system and therefore stimulates an immune response by lymphocytes

What is meant by ‘self’ and ‘non-self’?

Antigens act as markers on cell surface membranes. They are unique to each person.

Where are antigens found?

On abnormal body cells such as:

• cancer cells

• Virus infected cells

• Antigen presenting cells

• Pathogens such as bacteria or viruses

What are the white blood cells that carry out phagocytosis called?

Phagocytes

What type of response is phagocytosis?

Non-specific immune response

What do phagocytes do?

They engulf and digest foreign materials such as pathogens

Explain antigen presentation.

At the end of phagocytosis, the phagocyte will display the antigens of the pathogen on its cell surface membranes- it becomes an antigen presenting cell

This is important for the lymphocytes to carry out their role of specific immune response

Explain the process of phagocytosis.

1. The phagocyte is attracted to the pathogen by chemical products of the pathogen. It moved towards the pathogen along a concentration gradient.

2. The phagocyte has several receptors on its cell-surface membrane that attach to chemicals on the surface of the pathogen

3. Lysosomes within the phagocyte migrate towards the phagosome formed by engulfing the bacterium

4. The lysosomes release their lysozymes into the phagosome, where they hydrolyse the bacterium

5. The hydrolysis products of the bacterium are absorbed by the phagocyte

What produces antibodies?

B lymphocytes

Describe the structure of an antibody.

• y shaped

• 4 polypeptide chains

• Variable region

• Constant region

• Receptor binding site

• Heavy chain

• Light chain

• Antigen-binding site

How does an antigen-antibody complex form?

The specific binding sites fit precisely with the shape of the antigen to form the antigen-antibody complex

Explain how antibodies lead to the destruction of pathogens.

• antibodies do not destroy antigens directly, but prepare them for destruction

• FOR EXAMPLE: agglutination of bacterial cells: causes them to clump together to increase efficiency of phagocytosis, the antibodies themselves also act as markers that stimulate phagocytes

Explain specific immune response

• this response is specific to individual antigens

• Slower, but can provide long-term immunity

• Involves lymphocytes

• B lymphocytes provide humoral immunity

• T lymphocytes provide cell mediated immunity

T lymphocytes can only responded to what type of antigen?

An antigen that is presented on body cells suck as:

• infected cells

• Cancerous cells with altered antigens

• A phagocyte

• Transplanted cells

T helper cells

• There are a vast number of different Th cells each responding to different antigens

• receptors on a specific Th cell will fit exactly top the antigen

• The Th cell will divide rapidly to form genetically identical clones of cells

What is the role of cloned T helper cells?

• become memory cells to carry out a secondary response to a future infection by the same pathogen

• Stimulate B lymphocytes

• Stimulate phagocytes

• Activate cytotoxic T lymphocytes ( T killer lymphocytes)

What is the role of cytotoxic cells (Tc cells)?

• Tc cells are responsible for destroying harmful cells such as abnormal calls and infected cells by secreting chemicals such as performing, a protein that makes holes in cell membranes

Explain humoral immunity

• b lymphocytes (B cells ) provide humoral immunity by producing antibodies

• When a specific B cell encounters its specific antigen it is taken into the cell by endocytosis

• The antigen is then presented on the surface

• Th cells attach to the antigens and activate the B cells

• The B cells divide by mitosis to form a clone of B cells which produce the antibody specific to the antigen - monoclonal antibodies

What are the 2 types of humoral immunity?

• plasma cells secrete the antibodies- primary response

• Memory cells are responsible for the secondary response

Why don’t lymphocytes destroy our own cells?

• lymphocytes begin to develop in the foetus where they come into contact with self cells almost exclusively

• Any cells that have receptors to these cells antigens are destroyed or suppressed

• In adults, lymphocytes produced in bone marrow also initially only encounter self antigens

• Any which show in immune response undergo programmed cell death before they mature