chapter 4 - a tour of the cell

What are the two parts of cell theory?

1. All living things are made of one or more cells

2. all cells come from other cells

what did Matthias Schneider (a botanist) and Theodore Schwann propose in 1838-1839?

all living things are made up of one or more cells

what did Rudolph Virchow propose in 1855?

All cells come from other cells

How was the microscope discovered? When and by whom?

the microscope was discovered at the end of the 16th century, when Zacharius and Johannes Janssen, father and son glassmakers discovered that when placed together, layering pieces of glass had a magnifying effect. they got scared looking at the magnified church, they thought they were about to be punished

Who is Anton van Leeuwenhoek? What is he known as?

Anton van Leeuwenheok, known as “the father of microbiology” looked at tartar from his teeth under a microscope and discovered many times of microorganisms (1660, Holland)

How were cells named?

in England in 1665, Robert Hooke observed box like units in cork tissue. the shape of these units reminded him of cells in a monastery. he reported his findings to the Royal Society of London (published), and the units became known as cells

name 3 features of light compound microscopes

1. image reversal - images are upside down and backwards

2. total magnification - ocular lens magnification (10x) x objective lens magnification

3. resolving power - ability to see the details of small objects

a) how do light compound microscopes work?

b) how do electron compound microscopes work?

a) they pass visible light through a sample, and magnify cellular structures using multiple lenses

b) they focus a beam of electrons through a sample to take a black and white picture called an electron micrograph (which are often artificially coloured)

when were electron microscopes invented?

1960

what are the advantages and disadvantages of electron microscopes? (1 of each)

pros:

• electron microscopes have greater resolving power than light compound microscopes, magnifies up to 100,000x

cons:

• EMs cannot be used to study live organisms, as all samples must be dehydrated

what are the two types of electron microscopes? what is the function of each type?

1. Scanning electron microscopes (SEMs) are used to study the surface of the cell

2. Transmission electron microscopes (TEMs) are used to study the inside of the cell

what are the pros and cons of dissecting microscopes?

pros:

• no image reversal, allows 3D imaging and observation of larger live specimens

cons:

• have the lowest magnifications and resolutions

name two cells that can be seen without a microscope?

chicken eggs, neurons that make up the sciatic nerve

name 4 basic features of all cells

• a plasma/cell membrane

• DNA

• ribosomes that make proteins

• cytoplasm/cytosol

what are the biggest and smallest organelles?

the biggest organelle is the nucleus. the smallest organelles are ribosomes

what are the three parts of the nucleus?

nuclear envelope, nucleolus, chromatin

nuclear envelope (5)

• a double membrane enclosing the nucleus

• continuous with the ER

• not smooth, perforated with small openings called nuclear pores that are surrounded by proteins

• ribosomes can be bound to it

• part of the endomembrane system

nucleolus (3)

• site of rRNA (subunit) synthesis

• filled with nucleoplasm (cytoplasm of the nucleus)

• a nucleus has 1 or more nucleoli

chromatin (1)

• de-condensed chromosomes/ genetic material found in the nucleus

ribosomes (4)

• complexes of rRNA and protein

• found in PR and EU cells

• protein factories that build the cell’s proteins

• made up of two subunits, a large one and a small one

what are the two types of ribosomes?

free ribosomes, found in cytoplasm and bound ribosomes, embedded in the rough ER or nuclear envelope

what does the endomembrane system do (2)? what are the 6 parts of the endomembrane system?

the endomembrane system regulates protein traffic and performs metabolic functions. the six parts of the endomembrane system are the ER, Golgi apparatus, nuclear envelope, lysosomes, vacuoles and plasma membrane

what is the endoplasmic reticulum? (4)

• a network of membranes

• continuous with the nuclear envelope

• has two parts, the smooth ER and the rough ER

• only found in eukaryotic cells

smooth ER (5)

• continuous with RER

• lacks ribosomes

• involved in lipid synthesis

• detoxifies drugs and poisons

• stores calcium ions (which are important for muscle contraction)

rough ER (4)

• studded with ribosomes

• acts as a membrane factory for the cell

• aids in the synthesis of secretory proteins and other proteins (from embedded ribosomes)

• continuous with SER and nuclear envelope

Golgi apparatus (5)

• shipping and receiving centre of the cell

• consists of flattened, membranous sacs called cisternae

• receives products from the ER and modifies them

• manufactures certain macromolecules like cellulose

• sorts and packages materials into transport vesicles

what are the two sides of the Golgi? what does each side do?

• the two sides of the Golgi are the cis face and the trans face.

• The cis face is the receiving side of the Golgi, ex. receives proteins from the ER that need to be modified. 

• the trans face is the shipping side of the Golgi- it sends products of the Golgi in vesicles to other parts of the cell or the body

what are the 2 “fates” of vesicles leaving the Golgi?

1. vesicles stay in the cytoplasm and fuse with lysosomes

2. vesicles merge with the plasma membrane to release secretory proteins they are carrying

lysosomes (3)

• the cell’s digestive compartments (digestive systems)

• lysosomes are membranous sacs containing hydrolytic enzymes that can digest macromolecules (like proteins, fats, polysaccharides and nucleic acids)

• play a part in phagocytosis/ autophagy

what is phagocytosis? explain the process.

phagocytosis is a type of cellular eating. phagocytosis occurs when food vacuoles carrying food from outside the cell merge with lysosomes to break down the food for reuse

what is autophagy?

damaged cellular components are surrounded by specialized vesicles. the vesicles then merge with lysosomes that digest the damaged cellular components within the vesicles

what are the 3 types of vacuoles?

food vacuoles, contractile vacuoles and central vacuoles

what are vacuoles? (2)

• vacuoles are maintenance compartments that perform a variety of functions

• part of the endomembrane system

food vacuoles

food that has entered the cell through phagocytosis (an extended form of endocytosis) that merge with lysosomes for digestion

contractile vacuoles

found in many unicellular freshwater protists. as a form of osmoregulation, contractile vacuoles pump excess water out of the protists to maintain water balance.

central vacuoles (5)

• found in many mature plant cells

• store compounds, water, waste and pigments

• provide structural support

• plant cell nuclei are often pushed to the side by the central vacuole

• surrounded by a membrane called a tonoplast

what are tonoplasts?

membrane surrounding the central vacuole in plant cells

peroxisomes (3)

• found in plants and animals

• specialized metabolic compartments that contain enzymes that remove H atoms from certain molecules like toxins, transfer them to oxygen to produce H2O2

• the toxic H2O2 is then converted to H2O by a different enzyme

mitochondria (3)

• found in almost all eukaryotic cells

• sites of cellular respiration in plants and animals (and other eukaryotes)

• cells can have one mitochondrion or many mitochondria

and describe the structure of a mitochondrion

• consist of 2 membranes with an intermembrane space

• inner membrane is highly convoluted, and consists of folds called cristae to increase surface area

what is the cytoskeleton? what are the three types of fibres in the cytoskeleton?

a network of fibres involved in structural support and motility (of the cell and within the cell). the three types of fibres involved the cytoskeleton are microtubules, microfilaments and intermediate filaments

describe the size and structure of the three types of fibres

1. microtubules - biggest of the three fibres (~25nm), hollow tubes made of the protein tubulin, which gives microtubules their name

2. microfilaments - smallest of the three fibres (~7nm), made of intertwining strands of the protein actin

3. intermediate filaments - between microtubules and microfilaments in size, made of the protein keratin

name 4 functions of microtubules (“highways within the cell”)

1. shaping and supporting the cell

2. guiding movement of organelles

3. separating chromosomes during cell division

4. beating of cilia and flagella, which have microtubule skeletons (cell motility)

describe the structure of chloroplasts (4)

• have an inner and outer membrane with an intermembrane space

• contain stacked disks of individual thylakoids called granum

• chloroplast’s inner membrane is a fluid called stroma

• contain ribosomes

1. what organelle family are chloroplasts a part of?

2. what pigment to chloroplasts contain?

1. plastids

2. a green pigment called chlorophyll

label the parts of the chloroplast

peroxisomes (2), + how do they work?

• specialized metabolic compartments found in plants and animals

• contain an enzyme not used for digestion like lysosomes, but that remove hydrogen atoms from toxic molecules

• forms H2O2 from the H enzymatically removed from the toxin and H2O. the H2O2 is short lived, and another enzyme converts the H2O2 into H2O

cilia and flagella (3)

• have a 9:2 arrangement of microtubules

• between microtubule pairs is dynein, a bendable motor protein that helps the cilia and flagella move

• flagella are limited to one or a few per cell, while microtubules occur in large numbers, have the same cross section

centrosomes (3)

• microtubule organizing centre

• found only in animal cells

• made up of a pair of two perpendicular centrioles (each of which is made of 9 microtubule triplets arranged in a ring)

name 5 functions of microfilaments

1. form a 3D network inside the plasma membrane for maintenance of and changes to cell shape

2. muscle contraction (myosin will be present in addition to actin)

3. cytoplasmic streaming in plant cells

4. cell division in animals (cleavage furrow)

5. make up core of microvilli (which do not move like cilia)

what is cytoplasmic streaming?

the circular flow of cytoplasm within plant cells that spreads material distribution within plant cells

provide 2 examples of microfilaments being involved in contraction (and actin is present)

1. muscle cells contain 1000s of actin filaments that interdigitate with myosin filaments (arranged parallel to each other)

2. localized contractions drive ameboid movement

name 2 functions of intermediate filaments

1. supporting cell shape

2. fixing organelles in place

*not usually found in plants

which extracellular components are found in outside the plasma/cell membrane in..?

1. animals

2. plants

1. the extracellular matrix

2. cell wall

what are the 3 layers of the cell wall? describe each layer and its positioning

1. every plant cell has a primary cell wall made of cellulose fibres separating the plasma membrane from outside the cell

2. the middle lamella is a thin layer of glue like pectin between the primary cell walls of adjacent plant cells

3. some plant cells have a secondary cell wall, which is between the primary cell wall and the plasma membrane (within the primary cell wall) which are also made of cellulose

what are the three parts of the ECM in animal cells?

proteoglycans, collagen fibres and fibronectin

why do animal cells have an ECM while plant cells do not? what is the function of the ECM?

1. animal cells don’t have cell walls, so they are surrounded by an elaborate ECM which has several functions

2. functions in protection and support, movement and regulation

How is the ECM connected to animal cells?

fibronectin proteins bind to transmembrane receptor proteins embedded in the plasma membrane called integrins

what are the four types of intercellular junctions? which are found in plant cells and which are found in animal cells?

plasmodesmata (plants), desmosomes, tight junctions, gap junctions (animals)

label

plasmodesmata (2)

• channels that perforate plant cells walls

• water, small solutes and sometimes proteins and rna can pass from cell to cell through plasmodesmata

gap junctions

also known as communicating junctions, they provide cytoplasmic channels between adjacent cells

tight junctions

the plasma membranes of neighbouring cells are pressed together tightly, preventing the leakage of extracellular fluid

desmosomes

also known as anchoring junctions, they fasten cells together into strong sheets by linking the intermediate filaments cytoskeletons

which type of animal intercellular junction is most similar to plasmodesmata in plants?

gap junctions