Cell Membrane and prokaryotes

Question 1

Who was the first person who observed cells under a microscope? how did they describe what they saw?

Answer 1

It was Robert Hooke. He said he saw Little boxes, referring to cells.

Question 2

First to observe living cells?

Answer 2

Anton van Leeuwenhoek. He also made lenses and microscopes

Question 3

where were the moving animalcules from? who did this?

Answer 3

Anton van Leeuwenhoek Examined pond water and bacteria scraped from his teeth -described them as moving “animalcules”

Question 4

who are the three scientists that developed the cell theory? what did each of them say and when?

Answer 4

Matthias Schleiden, Theodor Schwann, and Rudolf Virchow.

1. Mathias = Plants were made of cells and plant embryos arose from a single cell
2. Theodor = All organisms are composed of one or more cells. The cell is the structural unit of life.
3. Rudolf = 3rd principle of cell theory: “cells can arise only by division from pre-existing cell”

Question 5

What are the three basic tenets of modern cell theory?

Answer 5

1. All living things are made up of cells
2. Cells are the basic unit of structure and function in living things
3. Living cells come only from other living cells

Question 6

The 9 fundamental properties of the cells

Answer 6

• Cells are highly complex and organized
• Cells possess a genetic program and the means to use it.
• Cells are capable of producing more of themselves
• Cells acquire and utilize energy
• Cells carry out a variety of chemical reactions
• Cells engage in mechanic activities
• Cells are able to respond to stimuli
• Cells are capable of self-regulation
• Cells evolve

Question 7

who performed the first culture of human cells? when? what type of cells did he culture?

Answer 7

1951
George Gey of Johns Hopkins University
• Malignant tumor from Henrietta Lacks –HeLa cells
Still cultured in labs today

Question 8

what do we mean by cells are complex? what is the consequence of this complexity?

Answer 8

Complex –consisting of many different and connected parts

The more complex a structure, the greater the number of parts that must be in their proper place,
the less tolerant of errors in the nature and interactions of the parts,
and the more regulation or control that must be exerted to maintain the system.

Question 9

what is the general morphology of bacteria ?

Answer 9

Nano 0.05-0.2 micro meters in diameter

To very large 600 x 80 micro meters

Question 10

why are bacteria small?

Answer 10

Nutrients and wastes are transported in and out of the cell via the cytoplasmic membrane.

The rate of Transport determines the metabolic rate and therefore the growth rate of microbial cells.

The smaller the size of the bacteria the larger the surface area of the cytoplasmic membrane to volume therefore the faster the potential growth rate

Question 11

what are the different types of shapes for bacteria?

Answer 11

Cocci
Bacilli
Filamentous - form long multinucleate filaments that made branch to produce a network called a mycelium

Spirilla - rigid spirals
Spirochetes - flexible spirals
Misc shapes and
Pleomorphic - variable in shape

Question 12

how is the prokaryotic cell organization? name them inner to outer.

Answer 12

• it has a cytoplasm which contains a variety of components
• plasma membrane
• periplasmic space with periplasm
• cell wall
• slime layer or capsule
• flagella and pili

Question 13

what is cytoplasm matrix? where is it and what are the 7 things found in it?

Answer 13

The cytoplasmic matrix is a substance lying between the plasma membrane and the nucleus which contains mostly water and a variety of components.

Found in it are:

1. Ribosomes
2. Proteins
3. Inclusion bodies
4. Organic materials
5. Inorganic materials
6. Carboxysomes
7. Gas vacoules

Question 14

what organic materials are found in cytoplasmic matrix?

Answer 14

• glycogen a polymer of glucose it is a carbon source
• poly beta hydroxybutyrate also a carbon source
• cyanophycin nitrogen source

Question 15

what inorganic materials are found in cytoplasmic matrix?

Answer 15

Polyphosphate or volutin it’s a phosphate source also there is iron and sulphur

Question 16

discuss carboxysomes and gas vacuoles.

Answer 16

Carboxysomes contain the enzyme ribulose 1.5 bisphosphate carboxylase which is important for incorporation of carbon dioxide.

Gas vacoules?

Question 17

what is the plasma membrane? what is it also called?

Answer 17

A plasma membrane also called inner membrane or cytoplasmic membrane is a phospholipid bilayer with proteins inserted into it.

Question 18

describe the structure and functions of plasma membrane.

Answer 18

Lipid bilayer.
Functions of plasma membrane:
1. Retains cytoplasm
2. The plasma membrane is a selectively permeable barrier it allows small neutral or charged molecules to come in (h2o, o2, co2). These can Transverse through the membrane.

But large molecules like glucose and ions or small charged atoms and protons H+ require specific transport systems.

3. Transport of nutrients and waste
4. Generation of energy, biosynthesis
5. Contains receptor proteins for environmental signals

Question 19

protoplast?

Answer 19

Cytoplasm + plasma membrane = protoplast

Question 20

what is the fluid mosaic model?

Answer 20

-the fluid mosaic model describes the structure of the plasma membrane as a mosaic of components including phospholipids cholesterol proteins and carbohydrates that gives the membrane a fluid like character.

Question 21

what are the three basic components of the structure of eubacterial membrane?

Answer 21

1. Phospholipid bilayer
2. Proteins
3. Hopanoids

Question 22

what is phospholipid bilayer and where is found?

Answer 22

The phospholipid bilayer

the bilayer is composed of two sheets each composed of phospholipids

nonpolar hydrophobic fatty acid ends of each of the two sheets of the bilayer they interact with each other

the polar hydrophilic water loving, face either the aqueous cytoplasm or the periplasm

Lipids are frequently bound to glycerol molecules in ether linkages

Question 23

why are there proteins on the plasma membrane?

Answer 23

Integral proteins
are inserted in the membrane amphipathic

Peripheral proteins
are loosely associated with the membrane they can be dissociated with salt

distribution and properties of proteins on each side of the bilayer are different therefore the functions of the two bilayers are different.

Question 24

hopanoids?

Answer 24

They are rigid planar Penta cyclic molecules similar to cholesterol that stabilize the membranes in some but not all eubacteria

Question 25

what is the basic structure of archaebacterial membranes?

Answer 25

Lipids are isoprenoids instead of fatty acids Ether linkage to glycerol instead of Ester some have a monolayer instead of by layer due to tetra ethers the diversity of membranes is related to the diverse habitats in which archaebacteria live for example thermophiles live at extremely high temperatures and have almost all tetra ethers which stabilizes the membrane at high temperatures

Question 26

in internal membranes, what are mesosomes?

Answer 26

Mesosomes are invaginations in the plasma membrane function unclear may be an artefact of sample preparation

Question 27

describe the cell wall and its functions.

Answer 27

The cell wall is a strong structural layer that lies outside the plasma membrane but does not include capsule or slime layer cell wall plus capsule equals cell envelope functions include shape protection from osmotic lysis defence against host immune response

Question 28

what are gram positive bacteria?

Answer 28

Gram-positive bacteria are bacteria with peptidoglycan, t e i c h o i c acid and l i p o t e i c h o i c acid

Question 29

what are gram negative bacteria?

Answer 29

Gram negative bacteria have peptidoglycan periplasmic space outer membrane proteins and lipo polysaccharide

Question 30

discuss the chemical composition of eubacterial cell walls.

Answer 30

Cell walls are made up of peptidoglycan also known as murein layer peptidoglycan is a polymer of two sugar derivatives called glycans its n a g and letter n a m. The nag is n acetyl glucosamine and the nam is n acetyl muramic acid. Connection of polymer strands in the different bacteria: 1. Gram-negative bacteria link between their amino acids is attached to one nam on one polymer and amino acid on nam on another polymer. 2. Gram-positive bacteria peptide interbridge typically five glycines that connects the peptides on different polymers

Question 31

nucleoid in bacteria. describe it.

Answer 31

The nucleoid of bacterial cell usually contains a single long continuous and frequently circularly arranged thread of double-stranded DNA called the bacterial chromosome. No histones Plasmids - small usually circular double-stranded DNA molecules called plasmids plasmids may carry genes for such activities as antibiotic resistance tolerance to Toxic metals the production of toxins and the synthesis of enzymes Plasmids can be transferred from one bacterium to another in fact plasmid DNA is used for Gene manipulation in biotechnology

Question 32

what are plasmids and where are they found?

Answer 32

A plasmid is a DNA molecule that is separate from and can replicate independently of the chromosomal DNA in bacteria they are double-stranded and in many cases circular plasmids usually occur naturally in bacteria but are sometimes found in eukaryotic organism

Question 33

describe mesosomes.

Answer 33

Mesosomes are invaginations of inner cytoplasmic membrane they are there to increase the surface area for metabolism they are in foldings of the cell membrane possible role in cell division photosynthetic pigments or respiratory chains

Question 34

what are fimbriae/ pili and why do bacteria have these?

Answer 34

Fimbriae/pili are projections from the cell membrane through the cell wall to permit specific attachment to surfaces found in gram negative bacteria they are shorter and finer than flagella they are composed of protein subunits called pilins adhesins are minor proteins at the tips of the pili responsible for the attachment

Question 35

ordinary pili vs sex pili

Answer 35

Ordinary Pili is for adherence of bacteria to host cells Sex pill is for attachment of donor and recipient cells in bacterial conjugation

Question 36

what are flagella? what is the protein it is composed of?

Answer 36

Flagella are threadlike appendages and they are composed of protein subunits called flagellin the flagella is a means to propel the bacteria it is a different what are two eukaryotic version flagella is very highly antigenic removed like if mechanically cut off or if it's removed by mechanical agitating, a new flagella is rapidly formed and the motility is rapidly restored

Question 37

if flagella is chopped off, what happens next?

Answer 37

The flagella grows back

Question 38

list the functions of cell membranes.

Answer 38

It separates interior cell contents from the surroundings forms a protective barrier and controls what moves in and out of the cell Maintains electric potential of the cell

Question 39

what are phospholipids? describe the components of their structure.

Answer 39

Phospholipids are the structural units of membranes they consist of one phosphate one variable one glycerol molecule 2 fatty acids saturated fatty acid and unsaturated fatty acid

Question 40

what happens when phospholipids come into contact with water? how do they arrange themselves?

Answer 40

When phospholipids come in contact with water and they will spontaneously arrange themselves in micelles may also form bilayers liposomes closed body or in a membrane The charged hydrophilic heads facing outward to interact with water the hydrophobic tails are facing inward to create nonpolar oily core un

Question 41

what is meant by hydrophobic and hydrophilic? how do these relate to phospholipids?

Answer 41

Hydrophobic means water fearing hydrophilic means water loving so what this means for phospholipids is that when they form the bilayer for cell membranes their heads Will line up and face the cytoplasm of water thingy and the tails will come in the middle and be away from the water

Question 42

--- represents fundamental organization of all biological membranes.

Answer 42

Lipid bilayer

Question 43

what is the framework of membranes called?

Answer 43

Phospholipids

Question 44

what are the 3 general categories of membrane proteins?

Answer 44

1. Integral proteins 2. Peripheral proteins 3. Lipid anchored proteins

Question 45

what are some of the properties of integral proteins?[2]

Answer 45

They are transmembranal and amphipathic

Question 46

what is meant by amphipathic? discuss

Answer 46

It means having a hydrophilic and hydrophobic region hydrophilic regions react with hydrophilic phospholipid heads hydrophobic regions form strong interactions with hydrophobic core of the phospholipid bilayer

Question 47

why are integral proteins well embedded in the membrane and difficult to remove experimentally?

Answer 47

Because of amphipathic property that they have.

Question 48

List the function of integral proteins.

Answer 48

1. They are specialised ports that freely admit selected ions like sodium and potassium 2. Transport proteins and facilitate movement of selected substances into and out of the cell 3. They are enzymes larger globular proteins that carry out enzyme functions while embedded in the membrane 4. Form a support that may form Bridges with cytoskeleton

Question 49

what are peripheral proteins? where are they found?

Answer 49

Peripheral proteins that also membrane proteins they are found on the surface of the membrane. They are held in place by either ionic interactions with charged phospholipid heads Or interaction with integral proteins they are easily extracted from the membrane with salt Solutions unlike integral proteins

Question 50

what holds peripheral proteins in place?

Answer 50

Ionic interactions with charged phospholipid heads or interaction with integral proteins

Question 51

how are peripheral proteins extracted from the membrane?

Answer 51

Salt solution

Question 52

lipid anchored proteins, what are they and where are they anchored?

Answer 52

Extend part of the way through the membrane but well into the core where they are anchored they are anchored in the core Anchorage is provided by lipid side chains which intermingle with those of the membrane.

Question 53

what provides anchorage for these proteins?

Answer 53

Lipids side chains which intermingle with those of the membrane.

Question 54

what is meant by glycocalyx? and its functions.

Answer 54

Glyco calyx means sugar coating appears as a fuzzy in distinct outermost layer on TEM.

Question 55

define glycoproteins. | define glycolipids. why they are outside?

Answer 55

Short chains of carbohydrate attached to the surface proteins and lipids they can either be glycoproteins or glycolipids Glycoproteins: Integral proteins with only their carbohydrate chains protruding from the surface Glycolipids: lipid tail anchored in phospholipid bilayer with the carbohydrate chain protruding from the surface

Question 56

what are their functions? [glycolipids and glycoproteins]

Answer 56

Glycolipid function is binding of bacterial cells to each other and to cell surfaces of organisms they invade. Glycoproteins act as receptors for chemical messengers and cell recognition glycolipids and glycoproteins on red blood cells are antigens used for determining Abo blood groups.

Question 57

briefly discuss the fluid mosaic model.

Answer 57

It refers to the fluid like properties of phospholipid bilayer and patchwork arrangement of its components model means it's still tentative the bilayer is a stable configuration for phospholipids but other molecules can move quite freely in the membrane because it is held together by hydrophobic forces or bonds which are weak forces molecules generally slide around but don't flip planes

Question 58

why can other molecules move easily in the membrane even though there's a bilayer?

Answer 58

Because the membrane has got hydrophobic bonds holding it which are weak forces

Question 59

---generally slide around but don't flip planes.

Answer 59

Molecules

Question 60

name 3 factors that the degree of fluidity (of the membrane) depends on.

Answer 60

The degree of fluidity of the cell membrane depends on number 1 which type of fatty acids predominate in the membrane number 2 depends on temperature number 3 depends on the amount of cholesterol

Question 61

what is the function of tight junctions? what is another name for tight junctions?

Answer 61

Tight junctions aka Occluding junctions (zonula occludens) Found: on the lateral surface of cells immediately below the luminal surface Functions of tight junctions: 1. Binds cells tightly together so luminal contents don't pass between the cells also known as zonula occludens. 2. Prevent movement of membrane components between different compartments for example integral proteins etc on apical surface from moving to lateral surface 3. Form interconnected ridges with no intercellular space

Question 62

describe the composition of tight junctions?

Answer 62

Composed of a complex of proteins which connect two membranes tightly together by forming a series of studs which appear as interconnected ridges with no intercellular space

Question 63

define adhering junctions. what is their function?

Answer 63

Adhering junctions are called anchoring junctions their function is to maintain cellular position there are different types of desmosomes(adhering junctions) 1. Belt desmosomes also known as zonula adherens 2. Spot desmosomes also known as macula adherens they form plaques just below cell membrane bound to cytoskeletal elements and to a similar structure in an adjacent cell or the extracellular Matrix.

Question 64

what are the different types of desmosomes? [2]

Answer 64

1. Zonula adherens | 2. Macula adherens

Question 65

what are gap junctions?

Answer 65

Gap junctions are communicating junctions

Question 66

what is a cluster of pores called?

Answer 66

Connexon. Each each connexon is aligned with a similar pore in an adjacent cell each connexon is made of six integral membrane proteins called connexins

Question 67

discuss what is meant by this cluster.

Answer 67

This is a cluster of pores called connexon, each is aligned with a similar pore in an adjacent cell, the cell next to it has a similar connexon so that they they can have an opening like a pipe to allow stuff to go through and each of these connexons is made of 6 integral proteins called connexins.

Question 68

what is the function of gap junctions?

Answer 68

So, gap junctions function as a channel between adjacent cells they function as a free passage of water small molecules some signalling molecules and positive ions they allow movement of excitation across sheets of muscle. the pore is closed by high concentrations of calcium Seals off apoptotic cells from neighboring cells

Question 69

what causes the closure of the gap junction pore?

Answer 69

The pore is closed by high concentrations of calcium

Question 70

define cilia and flagella.

Answer 70

They are mobile projections of the plasma membrane they are composed of microtubules core axoneme 9 microtubule doublets around a central - doublet (9 +2) Containing a basal body anchored in cell membrane. - 9 microtubule triplets same as centrioles Dyeins attached to doublet and enable movement

Question 71

what is core of actin filaments?

Answer 71

Core of actin filaments is attached to Terminal web of actin filament running under the apical surface of the cell

Question 72

discuss hemidesmosomes.

Answer 72

On Basal surface of the cell membrane in some epithelia They connect cell to basement membrane They consist of a plaque of integral proteins with intermediate filaments attached

Question 73

what are microvilli, discuss properties?

Answer 73

Microvilli are small finger-like projections of the cell membrane on the apical or luminal surface they are there to increase the surface area up to 30 fold they are found on epithelia with absorptive function like the intestinal lining they are up to 3000 microvilli per cell they are visible as a brush border on the light microscope.

Question 74

which side of the cell are microvilli found on?

Answer 74

Apical or luminal surface

Question 75

describe stereocilia. where are they found?

Answer 75

Stereocilia are longer than microvilli and they are branched they have a similar actin core to microvilli they are found in epididymis in male reproductive tract and they may have absorptive function

Question 76

differentiate between saturated and unsaturated fatty acids.

Answer 76

Saturated fatty acids have no double Bonds in their structure and unsaturated fatty acids have at least one double bond between its carbons in its structure

Question 77

what is the effect of the amount of cholesterol on membrane fluidity?

Answer 77

The more cholesterol the more fluid the membrane fluidity can increase or decrease in response to temperature as well but this is different for different cell types

Question 78

effect of temperature on fluidity of the membrane.

Answer 78

Cold temperature mean less fluidity some cells adjust phospholipid content of membrane when exposed to cold temperature

Question 79

what are the apical and basal surfaces in contact with?

Answer 79

Apical surface is in contact with the lumen and the basal surface is in contact with the basement membrane

Question 80

list the 3 types of junctions between cells.

Answer 80

1. Tight junctions - prevent movement of substances between cells 2. Adhering Junction - maintain cellular positions 3. Gap junctions - allow movement of substances the hemidesmosome is a junction between cells and basement membrane

Question 81

what are the functions of these types?

Answer 81

Tight junctions prevent movement of substances between cells adherens junctions maintain cellular position gap junctions allow movement of substances the junction between cells and basement membrane is called hemidesmosomes yo!

Question 82

what is the junction between cells and basement membrane called?

Answer 82

Hemidesmosome

Question 83

list the specialization (special structures) of the apical membrane.

Answer 83

Microvilli stereocilia cilia flagella

Question 84

what are tight junctions? where are they found?

Answer 84

Tight junctions are occluding junctions also called zonula occludens they are found on the lateral side or lateral surface of cells immediately below the luminal surface

Question 85

Ribosomes

Answer 85

Found in all eukaryotic and prokaryotic cells function is protein synthesis cells that have high rates of protein synthesis such as those that are actively growing have a larger numbers of ribosomes Ribosomes are composed of two subunits the 50s and 30s larger subunit and smaller subunit respectively and they have a type of RNA called ribosomal RNA prokaryotic ribosomes are called 70s ribosomes and those of eukaryotic cells are known as 80s ribosomes.