Cell structure

Question 1

Cell theory states that

Answer 1

1) All organisms are made of cell/s
2) Cells are the basis structural and functional unit of all organisms
3) All cells come from pre-existing cell (cell division)
4) Cells contain inherited information whose information is used for growth, functioning and development (1953 Noble Prize winners: Watson and Crick DNA Model)

Question 2

Eukaryotes vs Prokaryotes

Cellularity, membrane bound organelles?, DNA?

Answer 2

E: Generally multicellular: large numbers of different types of eukaryotic cells usually group together to form single organism –> P: Only ever unicellular: whole organism is just one cell

E: Has nucleus and other MBO e.g. mitochondria, ER –> P: does NOT have nucleus and any other MBO (doesn’t include ribosomes)

E: DNA found enclosed in the nucleus, linear, relatively large amounts –> P: NOT enclosed in the nucleus, found in cytoplasm, circular, relatively small amounts

Question 3

Prokaryotes vs Eukaryotes

Ribosomes?, Cell size, examples, size, reproduction

Answer 3

E: endoplasmic reticulum or cytoplasm –> P: ONLY in cytoplasm

E: LARGE –> P: SMALL

E: Animals, Plants, Fungi, Protists –> P: Bacteria, Archaea

E: 0.1-5.0µm –> P: 10-100µm

E: asexually or sexually –> P: asexually

Question 4

Eukaryotes and Prokaryotes common features

Answer 4

cell membrane, cytoplasm, and ribosomes  one point shared common ancestors

Question 5

History of microscopes

Answer 5

Microscopes have been key to the development of our understanding on cells. Scientists in the 1500s used handheld magnifying glasses to view objects of interest. In quest to see great detail they invented the first compound microscope: had 2 convex lenses placed on the end of a barrel, Robert Hooke in the 1660s, was able to view and draw the structure in cork that led to his use of the term ‘cella’ leading to ‘cell.

Question 6

Fluorescence microscope

Answer 6

• Similar to light microscope have better resolution
• Extra features to see certain parts of cells
• Cell structure “tagged” with a fluorescent dye
  Specimen is illuminated with a high-intensity source of light that causes the fluorescent substance to emit light.

Question 7

Light microscopes

How it works

Answer 7

• Use visible light and 2 lenses to make specimen look bigger.
  How it works:
• Light shines through thin specimen
• Light then travels through the objective and ocular lense
• As the light moves through the lenses its refracted to create a magnified images
  Preparation:
• Specimen will either be: whole organism, smear of cells or thin slice
• Staining: can be used in the preparation of specimens involving adding die to specimen. Only stains certain cell components increasing colour contrast between different structures.

Question 8

Light microscope

Prep, set up

Answer 8

• Put specimen on glass microscope slide, add some die to stain certain structures and add a drop of fluid + coverslip
  Set up:
• Put microsope on flat bench 5cm from edge  plug in and turn light on  put on lowest objective lense (4x)  place prep slide onto stage  use diaphragm to adjust amount of light passing through specimen  lower objective lens using course focus knob (close to but not touching specimen)  focus using course and fine focus knobs to get clear image (switch to higher objective if needed)

Question 9

Confocal microscope

Answer 9

one of the most advanced light microscopes
- Works by [passing a highly focused laser through the specimen
- Product = high quality image of a tiny part of the specimen
- Moke laser a little bit to get another image then computer enhances images and stitches them together to create a 3D image.

Question 10

Electron microscope

Answer 10

Uses beam of electrons and electromagnets to make specimen look bigger  electrons = small and sensitive (will bound off anything)  to achieve direct electron beam the internal chamber of the electron microscope is under vacuum conditions
- An electron gun shoots a beam of electrons towards specimen (controlled by electromagnets
- When electrons hit/interact with specimen the beam gets scattered
- The way the beams scatter depends on the structure of the specimen
- Scattering is detected by different machinery and a computer turns into an image (electron micrograph)
2 types: transmission and scanning

Question 11

TEM + SEM

Answer 11

Preparation: Treat specimens with chemicals – increase structural strength (otherwise electron beam will blow specimen to pieces), Dehydrated with alcohol (water evaporates instantly in vacuum: would destroy specimen)
Black + white

Question 12

TEM

Answer 12

• 1 broad electron beam shot at specimen (electrons pass through specimen)
• Specimen embedded in a resin before being cut into super thin slices
• Electron micrograph is a detailed image of the inner structure of the specimen
• Internal cell structures e.g. organelles, virus particles
• Magnify up to 1 500 000 x
• RESOLUTION = ~2nm
• 2D IMAGES

Question 13

SEM

Answer 13

1 super fine specimen is systematically scanned across the whole specimen
Coat specimen in a thin layer of gold, no need to slice
Electron micrograph is a detailed image of the outside of the specimen (gold layer causes electron beam to bounce off)
Surface of a pollen grain and insect exoskeleton
RESOLUTION ~ 10nm
3D IMAGES

Question 14

Light vs electron

Answer 14

Radiation type: Light, Electron
Purpose: Make magnified image of specimen
Magnification < 2000X, < 10, 000, 000X
Resolution: Lower (best resolution = 0.25µm) Higher due to shorter wavelength (best resolution = 0.0001µm)
Price: Lower Higher
Specimen: alive? Yes No
Colour: Yes No

Question 15

Resolution

Answer 15

shortest distance between 2 points on a specimen that can still be distinguished by the microscope as separate entities. HIGHER RES = CLEARER IMAGE  Better resolution allows scientists to study these structures at a molecular level, improving our understanding of cellular function, disease mechanisms (e.g., cancer, neurodegeneration), and potential drug targets.

Question 16

Magnification

Answer 16

Magnification: process of making something look bigger  how big the specimen appears to be compared to how big it actually is. Magnification = ocular lens x objective lens OR magnified size/actual size

Question 17

Measured length of cell

Answer 17

FOV (mm)/number of cells

Question 18

Actual length of cell (mm)

Answer 18

Measured length (mm)/magnification

Question 19

Scale
Micrometer conversion

Answer 19

actual length/length of drawing
1mm = 1000 µm

Question 20

Cell

Answer 20

smallest structural and functional unit of a living organism e.g. plants and animals: building blocks of life, every living thing is made up of them

Question 21

Organelles

Answer 21

an internal structure or part of the cell that is enclosed by a membrane and has a particular function.

Question 22

Cell (plasma) membrane

Answer 22

Location: Surrounds the cell forming a boundary between cell content and extracellular environment
Structure: Semi-fluid phospholipid bilayer where proteins are embedded.
Function: Forms boundary between cell and environment. Regulates movement of substances in and out of the cell. selectively permeable

Question 23

Ribosomes

Answer 23

Location: Free in the cytoplasm and bound to rough endoplasmic reticulum
Structure: Made of ribosomal RNA (rRNA) and protein. Composed of 2 subunits; larger and smaller one. Don’t have a membrane holding them together (aren’t technically organelle)
Function: non-membranous organelles that translate messenger RNA into polypeptides that later fold into proteins.

Question 24

Mitochondria

Answer 24

Function: Cytoplasm
Structure: Rod-shaped organelles in large numbers (especially in more active cells that require more energy e.g. liver cells contain 1000- 2000). double membrane; smooth outer and folded inner (more SA = increased rate of respiration. Function: Site of cellular respiration: combine oxygen w glucose to create ATP

Question 25

Endoplasmic reticulum

Answer 25

Structure: usually a continous network of flattened interconnected membranes Function: forms a communication system connection of pathways between the nucleus and cells enviro, allows intracellular transport, immense folding of the shets of membrane increases its surface area

Question 26

REM

Answer 26

Location:Continuous with the nuclear membrane and extending to the cytoplasm Structure: Complex system of interconnected membranous tubules studded with ribosomes. Function: Synthesis, folding and modification of proteins such as hormones. Transport of proteins to the Golgi body then secreted outside the cell. Membrane production

Question 27

SER

Answer 27

Location: Cytoplasm Structure: Similar system of interconnected membranous tubules like RER but lacking in ribosomes Function: Synthesis of lipids (e.g. cholesterol) Transport of these materials through the cell. Detoxification of drugs and poisons (high amounts are found in liver cells)

Question 28

Golgi apparatus

Answer 28

Location: Cytoplasm Structure: Flat membrane sacs stacked on top of each other (not interconnected) Function: Process and package substances cell has made e.g. proteins and lipids from ER. After processing the membrane pinches off around the substance to form a vesicle. Used then to transport substances wherever needed (in or out)

Question 29

Nucleus

Answer 29

Location: Large oval or spherical, generally in the centre of the cell. Structure: Double nuclear membrane; with tiny pores, contains nucleolus (contains RNA) Contains genetic material (form of DNA and proteins) needed for growth, repair and proper functioning. Acts as the control centre.

Question 30

Nucleolus

Answer 30

Location: Within the nucleus Structue: Dense granular region mainly made of proteins and RNA (ribonucleic acid) Function: Synthesis of ribosomal RNA

Question 31

Vacuoles

Answer 31

Location: Cytoplasm Structure: Membrane bound sac fluid filled sacs larger in plants because they give the cell structural turgidity (maintain shape) Function: Central vacuole of plants provides cell volume and stores inorganic ions and metabolic wastes. Give plant cell structural support (turgor pressure): water in vacuole pushes out against cell wall helping to maintain shape. A: small, impermanent P: Large, permanent

Question 32

Chloroplasts

Answer 32

Location: Within the cytoplasm of plant leaf cells Structure: Double membraned elliptical shaped organelles which contain their own DNA and a green pigment called chlorophyll. More surface area = increased rate of photosynthesis  efficiency of the cell Function: Capture light energy (sun) to perform photosynthesis (creates glucose)

Question 33

Cell wall

Answer 33

Location: Surrounds the plant cell and lies outside the plasma membrane. Structure: Exact substance varies depending on the type of cell Plant: cellulose; strands of cellulose have a little elasticity so they are somewhat flexible to resist pressure  permeable to most materials Function: Maintains cell shape (important for plants as the don’t have bones, protects cell and prevents excessive water uptake)

Question 34

Lysosomes

Answer 34

Location: Free in the cytoplasm Structure: Membrane bound sacs containing digestive enzymes Function: Needed to breakdown cellular waste and foreign particles

Question 35

Centrioles

Answer 35

Location: In the cytoplasm as apart of the cytoskeleton (next to or close to the nucleus) ANIMALS Structure: Pair of small cylindrical structures made up of microtubules Function: Mainly involved in cell division: produce the spindle which helps pull chromosomes apart

Question 36

Cytoskeleton

Answer 36

Location: Network throughout the cytoplasm Structure: Dynamic system of microtubules, microfilaments and intermediate filaments Function: Maintains shape and mechanical support of the cell, regulation of cellular activities and involved in cell movement.

Question 37

Cillia

Answer 37

Location: Many in number and extend along the entire surface of the plasma membrane Structure: Short hairlike structures Function: Move entire cells or move substances along the out surface of a cell e.g. cilia lining cells in the respiratory tract that move particular matter towards throat.

Question 38

Flagella

Answer 38

Extend from the plasma membrane Long hair like structures Move entire cell e.g. sperm

Question 39

Models in science are useful to

Answer 39

1) Help represent things that are very large or very small 2) Explain complex structures and processes more simply 3) Make predictions about expected results

Question 40

Fluid mosaic model

Answer 40

- A model for the cell membrane: refers to the different molecules distributed across the membrane - Proposed in 1972 by J singer and G Nicholson that better explained both microscopic observations and functions of the plasma membrane compared to earlier understandings. - Proposes a ‘lipid sea’ with ‘many and various proteins floating on and in it. - The model has evolved somewhat overtime but still best accounts for the structure and function of the plasma membrane for now…

Question 41

Cell membrane structure

Answer 41

- The plasma membrane is made up of primarily of a bilayer of phospholipids with embedded proteins, carbohydrates, glycoproteins, glycolipids and in animal cells cholesterol - Main fabric of the Cell membrane is composed of two layers of phospholidpids forming a phospholipid bilayer. Each phospholipid in these layers can be represented by a phosphate head and 2 lipid tails. The phosphate head is hydrophilic (‘water loving’) and faces outwards either towards the cytoplasm or the outside of the cell and the lipid tails are hydrophobic (water hating) face inwards - Within the phospholipid bilayer there are: 1) Carbohydrates: Glycoprotein: attached to a protein Glycolipid: attached to a lipid 2) Cholesterol Squished between phospholipids 3) Proteins Integral proteins: lodged deep in the phospholipids (permanent) Peripheral proteins: attached on the outside loosely (temporary) - Proteins molecules are scatted throughout and suspended in the bilayer

Question 42

Role of glycoprotein, glycolipid, cholesterol and channel protein

Answer 42

Glycoproteins: important role in cellular recognition and immune response and act as receptors for hormones. together with glyolipids they stabilise membrane strucutre Glycolipid: like gp act as surface receptors and stabilise membrane Chlolesterol: disturbs the close paching of the phospholipids, helps to regulate membrane fluidity, important for stability Channel proteins: some substances particularly ions or larger molecules are transported through membrane via them.

Question 43

Function cell membrane

Answer 43

- CM controls the exchange of materials between the internal and external environment of the cell separates intracellular fluid (cytoplasm) with extracellular fluid (watery enviro outside cell)  prokaryotic and eukaryotic cells. - Used to create compartments within the cell (organelles  eukaryotic only - Regulation: able to control which substances go through it: responsible for regulating contents of cell, it is selectively permeable: allows only certain molecules/ions in/out: substances required for cell function (e.g. glucose, oxygen, water) move in, waste substances move out  of cell either passive transport or active transport. - Allows cells to get chemicals they need and get rid of what it doesn’tneed - Involved in cell recognition and communication e.g. immune system in animals: important to recognise whether cell belings to orgaisn or an invader (glycoproteins, glycolipids, integral proteins)

Question 44

How molecules get through membrane

Answer 44

Small or uncharged molecules – move fast across the membrane. Large or charged molecules – pass through protein channels. Water – moves through hydrophilic pores (osmosis)

Question 45

Impermeable, permeable, semi-permeable

Answer 45

1) doesn;t allow any molecules to pass through it, doesnt have pores for them to pass through 2) allows all molecules to pass through it, has large spaces or pores 3) Semi permeable: only allows certain molecules to pass through and others are held back - small pores.

Question 46

Protoplasm

Answer 46

Structure: composed of the nucleus and cytoplasm Function: living content of the cell that is surrounded by the cell membrane, where the functions essential to like e.g making cellular products and respiration are carried out

Question 47

Cytoplasm

Answer 47

Part of the protoplasm outside of the nucleus, consists of a liquid called the cytosol in which there are dissolved chemical substances, organelles and insoluble granules. 90% of water: medium in which all cell chemicals are dissolved/suspended