2.1 - Cell structure

What is the stain used for chromosomes?

Acetic orocein binds to DNA and stains chromsomes dark red

What is the stain used for cytoplasm?

Eosin

What is the stain used for lipids?

Sudan red

Outline how a student could prepare a temporary mount of tissue for an optical microscope.

1. Obtain thin secton of tissue
2. Place plant tissue in a drop of water.
3. Stain tissue on a slide to make structres visible
4. Add coverslip

Describe how light microscopes work.

1. Lenses focus rays of light and magnify the view of a thin slice of specimen.
2. Different structures absorb different amounts and wavelengths of light.
3. Reflected light is transmitted to the observer via the objective lens and eyepiece.

Describe how a transmission electron microscope (TEM) works.

1.Pass a high energy beam of electrons through a thin slice of specimen.
2. More dense structures appear darker since they absorb more electrons.
3. Focus image onto fluorescent screen or photographic plate using magnetic lenses

Describe how a scanning electron microscope (SEM) works.

1. Focus beam of electrons onto a specimen's surface using electromagnetic lenses.
2. Reflected electrons hit a collecting device and are amplified to produce an image on a photographic plate

Describe how a laser scanning confocal microscope works.

1. Focus a laser beam onto a small area on a sample's surface using objective lenses.
2. Fluorophores in the sample emit photons.
3. Photomultiplier tube amplifies the signal onto a detector. An image is produced pixel by pixel in the correct order.

What is the equation for magnification?

Magnification \= size of image / size of object

Define magnification

the ratio of an object's image size to its real size

Define resolution

smallest separation distance at which 2 separate structures can be distinguished from one another

Why do samples need to be stained for light microscopes?

Coloured dye binds to the structures.
Facilitates absorption of wavelengths of light to produce image. Differential staining: contrast between heavily & lightly stained areas distinguishes structures.

Explain how to use an eyepiece graticule and stage micrometer to measure the size of a structure.

1. Place micrometer on stage to calibrate eyepiece graticule.
2. Line up scales on graticule and micrometer. Count how many graticule divisions are in 100μm on the micrometer.
3. Length of 1 eyepiece division \= 100μm / number of divisions
4. Use calibrated values to calculate actual length of structures.

What is the nuclear envelope?

double membrane that surrounds the nucleus

What is a dense nucleolus made of?

RNA and proteins assembled ribosomes

Describe the relationship between the organelles involved in the production and secretion of proteins

The ribosomes that synthesise proteins are attached to the rER. The Golgi apparatus, which modifies proteins for secretion, aligns with the rER

Describe the structure of a mitochondrion

Surrounded by double membrane folded inner membrane forms cristae: site of electron transport chain. Fluid matrix: contains mitochondrial DNA, respiratory enzymes, lipids, proteins.

What does a lysosome do?

Glycoprotein coat protects cell interior by digesting contents of phagosome and exocytosis of digestive enzymes

What are bacterial cells walls made out of?

Peptidoglycan

What are fungal cells walls made out of?

Chitin

What do eukaryotic cells have?

nucleus and membrane bound organelles

What is the cytoskeleton?

a network of protein filaments within the cytoplasm that move organelles from place to place within the cell; allowing some cells to move and muscles cells to contract

What is exocytosis?

a process by which the contents of a cell vacuole are released to the exterior through fusion of the vacuole membrane with the cell membrane.

What is endocytosis used for?

take in large molecules into the cell

What does ER stand for as an organelle?

endoplasmic reticulum

What are the different membrane bound organelles?

Mitochondria, Golgi apparatus and ER

Label an animal cell

What are the different parts of an animal cell?

Nucleus, nucleolus, mitochondrion, ribosome, Rough ER, nuclear envelope, lysosome, Golgi apparatus, plasma membrane and smooth ER

What are the different parts of a plant cell?

Mitochondrion, chloroplast, amyloplast, Golgi apparatus, smooth ER, ribosomes, nucleolus, nucleus, nuclear envelope, rough ER, plasma membrane, cell wall and vacuole

What does the nucleolus contain?

RNA and proteins

What is chromatin?

The genetic material consisting of DNA wound around histone proteins

What does the nuclear envelope do?

separates the nucleus from the cytoplasm

Where are ribosomes made?

nucleolus

What does the nucleus do?

Control center, stores the organism's genome, transmits genetic information and provides the instructions for protein synthesis

What is the RER?

rough endoplasmic reticulum - a system of membranes containing fluid filled cavities that are continuous with the nuclear membrane and it is coated with ribosomes

What is the function of the RER?

It transports substances from one area of a cell to another. It also provides a large surface area for ribosomes which assemble amino acids into proteins. These proteins actively pass through the membrane into the cisternae and are transported to the Golgi apparatus for modification and packing

What is the structure of the SER?

smooth endoplasmic reticulum - a system of membranes containing fluid filled cavities that are continuous with the nuclear membrane and it is coated with no ribosomes

What is the function of the SER?

It contain enzymes that catalyses reaction involved with lipid metabolism such as synthesis of cholesterol, lipids and steroid hormones. It is involved with absorption, synthesis and transport of lipids

What is the structure of Golgi apparatus?

A stack of membrane-bound flattened sacs. Secretory vesicles bring materials to and from the Golgi apparatus

What is the function of the Golgi apparatus?

It modifies the proteins and lipids delivered to it from the RER and prepares them for secretion, then delivers them to the cell membrane via a vesicle.
Responsible for the synthesis of lysosomes.

How are proteins modified?

- Adding sugar molecules to make glycoproteins
- Adding lipid molecules to make lipoproteins
- Being folded into their 3d shape

What happens after the proteins are packaged into vesticles?

They are pinched off and are either sorted in a cell or moved into the plasma membrane either to be incorporated into the plasma membrane or exported outside the cell

What is the structure of a vesicle?

A small fluid-filled sac in the cytoplasm, surrounded by a single membrane.

What is the function of a vesicle?

Transports substances in and out of the cell (via the plasma membrane) and between organelles.

What is the structure of mitochondria?

Double membraned structure where the inner membrane is highly folded into Cristae to increase inner surface area.

How big is the mitochondria in a eukaryotic cell?

2- 5 micrometers long

What is the function of the mitochondria?

Site of aerobic respiration, where ATP is
produced. They are self-replicating, so more can be made as needed for cells requiring large amounts of energy.

What is the structure of chloroplasts?

A double outer membrane and a complex arrangement of internal membranes that form thylakoids (which contain chlorophyll).
Thylakoids are grouped into stacks called grana, joined by intergranal lamellae. Fluid-filled matrix is called the stroma.

What is the function of chloroplasts?

Site where photosynthesis takes place.
Grana; Light energy is trapped by chlorophyll and used to make ATP & water is split into ions.
Stroma: Where energy from ATP is used to make carbs

What is the structure of a vacuole?

Surrounded by a membrane called the
tonoplast.
Contains fluid.

What is the function of a vacuole?

Only plant cells have a permanent vacuole.
Filled with water and solutes and maintains cell stability, as when full pushed against cell wall, making cell turgid.

What are the structures of lysosomes?

A round organelle surrounded by a single membrane, with no clear internal structure.
These are small bags formed by the Golgi apparatus.

What is the function of lysosomes?

Contain powerful hydrolytic (digestive) enzymes.
Can engulf old cell organelles and foreign matter, digest them and recycle the material.
Often abundant in phagocytic cells that can ingest or invade pathogens.

What is the structure of plasma membrane?

The membrane found on the surface of animal and just inside cell wall of plant cells and prokaryotic cells.
Mainly made of lipids and protein.

What is the function of plasma membrane?

Acts like a barrier to the cell, controlling what enters and leaves due to the differential permeability to different biological molecules and due to protein carriers that pump substances in and out.

What is the structure of cillia?

Small, hair-like structures found on the surface membrane of some animal cells.
Cross-section shows they have an outer membrane and a ring of 9 pairs of protein microtubules, with a single pair of microtubules in the middle.

What is the function of cillia?

Microtubules allow cilia to move. Movement of cilia pushes substances along the cell surface.
Occur in large numbers along cell surface.
Nearly all cells in the body have one cilium that acts as an antenna and contains receptors to detect environment.

What is the structure of flagellum?

Small, hair-like structures that stick out from the cell surface and are surrounded by plasma membrane.
Cross-section shows they have an outer membrane and a ring of 9 pairs of protein microtubules, with 2 microtubules in the middle.

What is the function of flagellum?

Microtubules contract to make the flagellum move and propel cell forwards.

What is the structure of ribosomes?

Small spherical organelles (20nm in diameter).
Each ribosome consists of 2 sub-units.
Made up of proteins and ribosomal RNA.
Not surrounded by a membrane.

What is the function of ribosomes?

Site where proteins are made. Ribosomes attached to RER exterior make proteins to be exported outside cell.
Free-floating ribosomes in cytoplasm make proteins to be used inside the cell.

What is the structure of centrioles?

Consists of 2 bundles of microtubules at right angles to each other.
Microtubules made of tubulin protein subunits and arranged to form a cylinder.

What is the function of centrioles?

Involved with the separation of chromosomes during cell division.
Chromosomes attach to middle of spindle and motor proteins walk along the tubulin threads,
pulling chromosomes apart.

What is the structure of celluose cell wall?

A rigid structure that surrounds the plant cells.
Made from bundles of cellulose fibres

What is the function of celluose cell wall?

Strong and can prevent plant cells from bursting.
Provides strength and support.
Maintain cell shape
Permeable due to plasmodesmata (pores within walls) and allow solutions through.

What is the structure of a cytoskeleton?

Rod-like microfilaments made of subunits of actin
(protein) forming a polymer. Intermediate filaments about 10 nm in diameter. Straight, cylindrical microtubules, made of tubulin protein subunits and is about 18-30 nm.

What are the cytopskeleton motor proteins?

The cytoskeletal motor proteins, myosins, kinesins and dyneins, are molecular motors. They are also enzymes and have a site that binds to and allows
hydrolysis of ATP for an energy source.

What is the function of a cytoskeleton?

Cellular movement e.g. cilia and flagella contain microtubules that are responsible for moving them. Intracellular movement of organelles and substances within the cell. Strength and support.

What are microfilaments?

Within the cytoplasm
give support and mechanical strength.
Keep the cell's shape stable and allow cell movement.

What are intermediate filaments?

They anchor the nucleus within the cytoplasm.
They extend between cells in some tissues, between special junctions, enabling cell-cell signalling.
Allow cells to adhere to a basement membrane, stabilising tissues.

What are microtubules?

Provide shape and support to cells, help
transport substances and organelles through the cytoplasm.
They form the track along which motor
proteins move, taking
organelles along with them from one part
of the cell to another.
They form the spindle before a cell divides that move the chromosomes to opposite ends of the cell.

What is the 1st step for making and secreting a protein?

1) mRNA copy of the instructions (gene) for insulin is made in the nucleus.

What is the 2nd step for making and secreting a protein?

2) mRNA leaves the nucleus through a nuclear pore.

What is the 3rd step for making and secreting a protein?

3) mRNA attaches to a ribosome on the RER. The ribosome reads the instructions to assemble the protein (insulin).

What is the 4th step for making and secreting a protein?

4) Insulin molecules are 'pinched off' in vesicles and travel towards the Golgi apparatus.

What is the 5th step for making and secreting a protein?

5) Vesicle fuses with Golgi apparatus.

What is the 6th step for making and secreting a protein?

6) Golgi apparatus processes and packages insulin molecules ready for release.

What is the 7th step for making and secreting a protein?

7) Packaged insulin molecules are 'pinched off' in vesicles from the Golgi apparatus and move towards the plasma membrane.

What is the 8th step for making and secreting a protein?

8) Vesicle fuses with plasma membrane.

What is the 9th step for making and secreting a protein?

9) Plasma membrane opens to release insulin molecules outside cell.

What are the differences between prokaryotic and eukaryotic cells?

Prokaryotic are much smaller, less well developed cytoskeleton with no centrioles, no nucleus, no membrane bound organelles and a wall made from peptidoglycan and not cellulose. They also have smaller ribosomes and naked DNA.

What do prokayotes have?

Protective waxy capsule surrounding the cell wall, plasmids, flagella and pilli

What is pilli?

short hair like structure. helps prokaryotes stick to other cells and can be used to transfer genetic material between cells

infolding of membrane

may form a photosynthetic membrane or carry out nitrogen fixaton

What is mesosome?

Infolding of plasma membrane, associated with DNA during cell division and helps with formation of new cells wall

Prokaryotic Organelles - DNA

Tends to be a single DNA molecule supercoiled to
make it more compact.
The genes on the
chromosome are grouped into operons. This means that a number of genes are switched on or off at the same time.

Prokaryotic Organelles - Ribosomes

Smaller than those found in eukaryotic cells. Larger eukaryotic ribosomes are designated 80S and smaller prokaryotic ribosomes, 70S. Both are involved in protein synthesis, however, 80S ribosomes are involved in the formation of more complex ribosomes.

Prokaryotic Organelles - Cell Wall

Cell wall is made from peptidoglycan (also known as murein).
It is a complex polymer formed from amino acids and sugars.

Prokaryotic Organelles - Flagella

Is thinner than those found in eukaryotes and has a different arrangement.
The energy to rotate the
filament is supplied by the process of chemiosmosis
(not from ATP).
The flagellum of a
bacterium is attached to the cell membrane by a basal body and rotated by a molecular motor.

What is the cell wall of prokaryotic cells made out of?

Peptidoglycan

What is the cell wall of eukaryotic cells made out of?

Chitin in fungi, cellulose in plants, not present in animals

What is the size of ribosomes in prokaryotic cells?

70S

What is the size of ribosomes in eukaryotic cells?

80S

How does a prokaryotic cell divide?

binary fission

Name two features of plant cells that are not features of animal cells.

cell wall and chloroplasts

Name one structure present in animal cells that is not present in plant cells

centriole, lysosomes, cilia, flagella

Describe the roles of the cytoskeleton.

maintains shape, movement of cilia, changing shape of cell, movement of chromosomes

The pancreas is an organ that secretes protease enzymes. Outline how the organelles in pancreatic cells work together to produce and release these protein molecules from the cells

nucleus, contains gene (for protein)
ribosomes / rough endoplasmic reticulum / RER, site of, protein synthesis
vesicles for transport
Golgi processes and modifies the proteins
Vesicles fuse to cell surface

Suggest why antibodies specific to nuclear proteins are not normally made.

nuclear proteins normally, hidden in nucleus / not exposed to tissue fluids

1. Which of the following statements is / are true?
Statement 1: Microtubules are part of the '9 + 2' formation in bacterial flagella. Statement 2: Microtubules can be prevented from functioning by a respiratory inhibitor.
Statement 3: Microtubules are involved in moving chromosomes from the equator to the poles of the cell during mitosis.

Only 2 and 3