C1: Cell Structure

Vocabulary flashcards reviewing cellular biology organelles, structures, microscopy measurements, and comparisons based on the lecture notes.

Unit conversions (cm → mm → ųm → nm)

$$1\,\text{cm} = 10\,\text{mm} = 10\,000\,\mu\text{m} = 10\,000\,000\,\text{nm}$$

What is the diameter of a typical plant cell?

100 ųm

What is the diameter of a typical animal cell?

40 ųm

Name the structures that plant and animal cells have in common. (CB pg 5)

• nucleus with nucleolus and chromatin

• cytoplasm containing mitochondria, Golgi apparatus and other small structures

• cell surface membrane

Name the structures that are found in plant cells only. (CB pg 5)

• chloroplast

• large permanent central vacuole

• cell wall with middle lamella and plasmodesmata

Name the structure that is only found in animal cells. (CB pg 5)

Centriole

What is the meaning of resolution in microscopy?

• The ability to distinguish between two separate points

• The higher the resolution, the greater the detail that can be seen

• Greater in electron microscopes than light microscopes because the wavelength of an electron is shorter than the wavelength of light.

Nucleus

Structure:

• has double-membrane,

• has chromatin, nucleolus, and surrounded by nuclear envelope

Function

• Contain genetic materials

• Controls cell activities

Nucleolus

Structure:

• made of loops of DNA from several chromosomes

• deeply staining material in the nucleus

• rounded structure

Function:

• Make ribosomes (combine mRNA with proteins)

Chromatin

Structure:

• deeply staining material in the nucleus

• mass of coiled threads

Function:

• chromatin threads coil together to form chromosomes

Nuclear envelope

Structure:

• continuous with the endoplasmic reticulum

• double membrane

• has nuclear pore

Function:

• Allow exchange of materials between the nucleus and the cytoplasm (mRNA and ribosomes)

• Substance leaving the nucleus: mRNA, tRNA, ribosomes

• Substance entering nucleus: proteins (to make ribosomes), nucleotides, ATP, hormones such as thyroid hormone T3

Cell surface membrane

• a selectively permeable boundary enclosing the cytoplasm

• regulates the movement of substances in and out of the cell

• contains molecules essential for cell signalling and recognition.

Rough Endoplasmic Reticulum (RER)

Structure:

• Has ribosomes on surface

• Connected cisternae is connected to nuclear envelope

• Flattened shape of cisternae/membranous sacs

• Vesicles contain protein

Function:

• make, modify and transport proteins from transport vesicles to Golgi apparatus

Smooth Endoplasmic Reticulum (SER)

Structure:

• Tubular/looped

• Connected cisternae

• No ribosomes

• Vesicles contain lipids

Function:

• Make lipids and steroids such as cholesterol

• Detoxify the body from metabolic wastes and drugs / drug metabolism

• Makes reproductive hormones such as oestrogen and progesterone

• Major storage site for calcium ions

• Abundant in muscle cells where calcium ions are involved in muscle contraction

Mitochondria

Structure:

• double membrane

• inner membrane folded to form cristae, which projects into the interior called matrix

• Has circular DNA and 70S ribosomes

• can move, change shape and divide

Functions:

• Synthesise ATP via cellular respiration

• Synthesise lipids

ATP

• Adenosine triphosphate

• Made of a ribose, adenosine and three phosphate groyps

Golgi apparatus (Golgi body or Golgi complex)

Structure:

• flattened/bent/curved

• Form secretory vesicles that contain protein

• Some vesicles mature to become lysosome inside the cell

Function:

• processes/modifies proteins

Lysosomes

• Contain digestive enzymes

• Break down waste substances and old organelles

• Work fastest in acidic pH

• Contain enzymes such as protease, lipase and nuclease which break down protein, lipids and nucleic acids respectively

Functions:

• Engulf and destroy unwanted cell components such as molecules or organelles

• Endocytosis

• Exocytosis

• Self digestion (autolysis)

80S Ribosomes

• larger type of ribosome found in eukaryotic cells

• located freely in the cytoplasm and attached to the rough endoplasmic reticulum

70S Ribosomes

• smaller type of ribosome found in prokaryotic cells

• Found in chloroplasts and mitochondria

Ribosome

• makes protein

• 70S: chloroplast and mitochondria

• 80S: cytoplasm and RER

Centrioles

Structure:

• exist as a pair

• Arrange in right angle to each other

• Contain a ring of 9 triplets microtubule

Function:

• make cilia and flagella

Microtubules

Structure:

• Long, rigid, hollow tubes

• Combine with actin filaments and intermediate filaments to from cytoskeleton

• Made of protein called tubulin (alpha and beta tubulin) that combine together to form dimers

• Dimers join together end to end to form protofilaments

• 13 protofilaments line up in a ring to form a cylinder with a hollow centre (microtubule)

Function:

• determine/maintain the shape of cell

Centrosome

• act as microtubule organising centres (MTOC)

• form spindle fibre during cell division

Cilium/cilia

• A hair-like projection extending from a cell surface

• Short and many cilia per cell

• Motion: back and forth motion, moving ecf past cells

Flagellum/flagella

• Long and one or few per cell

• Motion: wave-like movement/snake-like motion, propel through ecf

Function of flagella and cilia

Aid in the movement of cell

Microvilli

• folding on cell surface membrane

• Increase the surface area for absorption or exchange of materials

Chloroplasts

Structure:

• double-membrane

• contain stroma, thylakoid stacks called grana connected by lamella

• has circular DNA (contain genetic code to make protein for photosynthesis) and 70S ribosomes.

• contain starch granules (product of photosynthesis)

Function:

• Absorb light energy during photosynthesis

Cell wall

• Gives the cell a definite shape

• Prevents the cell from bursting when water enters through osmosis

• Porous to allow the movement of substances to the cell surface

Plasmodesma/plasmodesmata

• Linked to neighbouring cells by means of fine strands of cytoplasm

• Allow the movement of substances (organic substances, ions, water, amino acids, sugars) between cells

Large central/permanent vacuole and tonoplast

• help regulate osmotic pressure of the cells

• Maintain cell turgidity

Prokaryotic Cells

• Small ($1-5\,\mu\text{m}$)

• typically unicellular organisms

• lacking a nucleus or membrane-bound organelles

Eukaryotic Cells

• Larger (up to $40\,\mu\text{m}$)

• typically multicellular cells containing a true nucleus, membrane-bound organelles, linear chromosomes with histones, and 80S ribosomes.

Compare prokaryotes and eukaryotes

Endosymbiont theory

• Mitochondrion and chloroplast have 70S ribosomes and circular DNA like bacterium.

• Mitochondrion and chloroplast are in fact ancient bacteria which now live inside larger cells of animals and plants.

• This is known as endosymbiont theory.

• ‘Endo’ means inside and a ‘symbiont’ is an organism which lives in a mutually beneficial relationship with another organism.

Viruses

• acellular/not made of cells

• has a protein coat/capsid which is made from capsomere

• Size: 15 nm to 1000 nm

Capsid

The outer protein coat of a virus that encloses its genetic material and may feature attachment proteins for host cell entry.

Types of microscopes

• Light microscope

• Electron microscope

1. Transmission electron microscope (TEM)

2. Scanning electron microscope (SER)

Label the parts of a light microscope and state their functions

Why organelles such as mitochondrion look different?

• Have different shape

• Have different orientation

• Cut at different sections

• Mitochondrion → divides

Transmission electron micrograph (TEM)

• Shows internal structures/details of organelles (e.g. double membrane)

• Show very thin sections through the cell

• Show 2D / flat views of cell structure

• Image is in one plane

Scanning electron micrograph (SEM)

• Show outer/external view of cell structure/organelles

• Good focus with different depth

• Show surface, contour, 3D views

Compare light microscope and electron microscope

What are the advantages of using an electron microscope rather than a light microscope?

• EM has higher resolution because of shorter wavelength

• The solution is equal to half the wavelength

• Resolution of light microscope is 0.2 ųm / 200 nm

• Resolution of electron microscope is 0.0005 ųm / 0.5 nm

• More detail can be seen/much clearer at the same magnification