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Bio1MGC > Cell structures > Flashcards

Cell structures Flashcards

1
Q

Features of the nucleus

A

nuclear envelope surrounds
nuclear pores perforate envelope
contains DNA organised into chromosomes
nucleolus - complex of rRNA and proteins - ribosoomes

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2
Q

Features of the nuclear envelope

A

Surrounds nucleus
Double membrane – each a lipid bilayer with proteins
Each membrane separated by a narrow space (20-40 nm)
Perforated by pore structures
Pore structures lined by pore complex which controls the entry and exit of proteins, RNA and macromolecules

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3
Q

What is the nucleolus made from?

A

rRNA (ribosomal RNA) and proteins
a region rather than bound
proteins come from the cytosol

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4
Q

Does every cell have a nucleolus?

A

only visible in non dividing cells (disappears during mitosis)
Sometimes there are two or more nucleoli - the number depends on the species and the stage of the cells cell’s reproductive cycle

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5
Q

what is the function of the nucleolus

A

synthesises ribosomal RNA from instructions in the DNA
Proteins imported from the cytosol are assembled with rRNA into the small and large units of the ribosomes
Ribosome subunits exit through nuclear pores to cytoplasm where they join to form a ribosome

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6
Q

Where are ribosomes made?

A

Ribosomes are synthesised in the nucleolus
In the nucleolus proteins and rRNA are assembled into large and small subunits of the ribosomes
Subunits are then exported through nuclear pores to the cytoplasm

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7
Q

Are ribosomes organelles?

A

Ribosomes are not membrane bound and so are not considered to be organelles

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8
Q

What is the nuclear lamina

A

The nuclear lamina is a netlike array of proteins filaments found on the nuclear side of the nuclear envelope
Maintain the shape of the nucleus
May help organise genetic material

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9
Q

what is the nuclear matrix

A

The nuclear matrix is a framework of protein fibres extending throughout the nuclear interior

May help organise genetic material

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10
Q

what is the function of ribosomes

A

protein synthesis

rRNAs carry out peptidyl transferase activity - protein synthesis

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11
Q

What is the structure of ribosomes

A

large and small units

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12
Q

Are ribosomes present in all cells

A

Eukaryotic cells have ribosomes
Prokaryotes have some ribosomes but they are smaller
cells that have high rates of protein synthesis have more ribosomes as well as prominent nucleoli e.g. pancreatic cells which need to produce a lot of insulin and other digestive enzymes

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13
Q

what is the difference between free and bound ribosomes

A

Free ribosomes are found floating in the cytosol

Bound ribosomes are attached to the ER or the nuclear envelope

Proteins made in free ribosomes function in the cytosol e.g. enzymes

Proteins made in bound ribosomes – used in membranes / lysosomes or exit the cell e.g. digestive enzymes

Bound and free ribosomes are structurally identical and can play either role at different times

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14
Q

What role do ribosomes play in carrying out genetic instructions?

A

Ribosomes translate the genetic message carried from the DNA in the nucleus by mRNA into a polypeptide chain

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15
Q

What cellular structures make up the endomembrane system?

A 
Nuclear envelope
Endoplasmic reticulum
Golgi apparatus
Lysosomes
Vesicles and vacculoles
Plasma membrane
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16
Q

where are bound ribosomes located

A

bound ribosomes are attached to the outside of the endoplasmic reticulum or the nuclear envelope

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17
Q

where are free ribosomes located

A

free ribosomes are located in the cytosol

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18
Q

What happens to proteins made in free ribosomes?

A

free ribosomes are suspended in the cytosol and most of the proteins they make are used within the cytosol for example enzymes that catalyse the first steps of sugar breakdown

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19
Q

what happens to proteins made in bound ribosomes

A

bound ribosomes (attached to ER and nuclear envelope) are inserted into membranes/ for packaging into certain organelles like the lysosomes or for export out of the cell

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20
Q

what is the structure of the ER

A

Network of membranous tubules and sacs called cisternae
The ER membrane separates the internal compartment of the ER – called the ER lumen (cavity) or cisternal space from the cytosol
The Er membrane is continuous with the nuclear envelope

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21
Q

what are cisternae?

A

Sacs in the ER

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22
Q

What is the ER lumen?

A

internal compartment of the ER
cisternal space
separated from cytosol
because the ER membrane is continuous with the nuclear envelope, the space between the two membranes of the envelope is continuous with the lumen of the ER

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23
Q

how are the nuclear envelope and the ER connected

A

the ER membrane is continuous with the nuclear envelope

the space between the two membranes of the nuclear envelope is continuous with the ER lumen

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24
Q

what are the two regions of the ER

A

smooth Er and rough ER

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25
Q

how are the smooth ER and rough ER different?

A

smooth ER lacks ribosomes

rough ER studded with ribosomes on the outer surface of the membrane

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26
Q

where are ribosomes found in the cell

A

ribosomes attach to the outer surface of the rough ER and also to the cytoplasmic side of the nuclear envelope

Free ribosomes also found in cytosol

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27
Q

what are the functions of the smooth ER

A

synthesis of lipids
metabolism of carbohydrates
detoxification of drugs and poisons
storage of calcium ions

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28
Q

what types of lipids are produced in the smooth ER

A

oils
steroids e.g. sex hormones
new membrane phospholipids

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29
Q

what are the functions of the rough ER?

A

aids in the synthesis of secretory and other proteins on bound ribosomes
adds carbohydrates to proteins to make glycoproteins
produces new membrane

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30
Q

how does the rough ER function in making secretory proteins

A

polypeptide chain forms from ribosome
enters the lumen and folds to functional shape
in the lumen carbohydrates are attached to form glycoproteins (enzymes built into the ER membrane)
ER membrane keeps new proteins separate from cytosol
ER makes vesicles

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31
Q

what are transport vesicles

A

Vesicles that transit from one part of the cell to another
transport vesicles bud off from a region of the rough ER called the transitional ER
after leaving the ER many transport vesicles travel to the golgi apparatus

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32
Q

what is the function of the golgi apparatus

A 
modifies products of ER
stores products
sends products to other destinations
receives and dispatches transport vesicles
manufactures some macromolecules
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33
Q

what is the structure of the golgi apparatus?

A

group of associated flattened membranous sacs - cisternae (unlike ER these sacs are not connected)
membrane separates internal space from cytosol

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34
Q

what are the two sides of the golgi?

A

cis face - located near the ER / receiving vesicles containing ER products
trans face - shipping department - dispatches vesicles that pinch off and travel to other sites

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35
Q

How does the golgi function to modify products

A

products are modified as they move from the cis to the trans region
glycoproteins formed in the ER have their carbohydrates modified (glycosolation)
membrane phospholipids also altered

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36
Q

what macromolecules are made in the golgi apparatus?

A

many polysaccarides secreted by cells are made in the golgi e.g. pectins

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37
Q

how does the golgi sort products before dispatch

A

the golgi sorts products and targets them for various parts of the cell
attach molecular identification tags like phosphate groups
transport vesicles may have external molecules that recognise docking sites on the surface of organelles or on the plasma membrane

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38
Q

what is the structure of cell membranes

A

cell membranes consist of a double layer of phospholipids
hydrophillic parts are in contact with the aqueous solutions inside and outside the cell
hydrophobic parts are inside and not in contact with liquids
embedded within and attached to the surface are diverse proteins

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39
Q

How does the plasma membrane contribute to cellular metabolism

A

many enzymes built into membranes

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40
Q

what is the structure of a lysosome?

A

membranous sac filled with hydrolytic enzymes

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41
Q

how is a lysosome made

A

hydrolytic enzymes and lysosome membranes form in the rough ER
transferred to golgi for further processing
lysosomes bud from the trans face of the golgi

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42
Q

what is phagocytosis?

A

lysosomes digest (hydrolyse) materials taken into the cell
vacuole taken into the cell fuses with a lysosome whose enzymes digest the food
e.g. amoeba and other unicellular eukaryotes eat by engulfing smaller organisms - make vacuoles
some human cells carry out phagocytosis e.g. white blood cells destroy bacteria

43
Q

what is autophagy?

A

lysosomes recycle intracellular materials / cell’s organic material
a damaged organelle or small amount of cytosol becomes surrounded by double membrane and the lysosome fuses with it

44
Q

what is a vacuole?

A

large vesicle derived from the endoplasmic reticulum and golgi apparatus
part of the cell’s endomembrane system
compartment that has different conditions to cytosol

45
Q

what are contractile vacuoles

A

unicellular eukaryotes living in fresh water
pump excess water out of the cell
maintain concentration of ions and molecules inside the cell

46
Q

do plant and fungi cells have lysosomes?

A

No - enzymatic hydrolysis is carried out in vacuoles

47
Q

what are the functions of vacuoles?

A 
food particles - digestion 
contractile vacuoles
act like lysosomes in plants - break down wastes
in plants may store compounds - storage
cell growth and protection
48
Q

what is the central vacuole

A

found in plant cells
largest compartment in plant cells
contains cell sap (store of inorganic ions)
enlarge as the plant absorbs water

49
Q

what are the distinctions between the rough and smooth ER?

A

presence of ribosomes on rough ER
both types of ER make phospholipids
membrane proteins and secretory proteins are produced on the ribosomes of the rough ER
the smooth ER functions in detoxification, carbohydrate metabolism and storage of calcium ions

50
Q

how are mitochondria and chloroplasts similar

A

both convert energy to forms that cells can use for work
mitochondria - cellular respiration
chloroplasts - photosynthesis

51
Q

what is evidence for the endosymbiont theory

A

both mitochondria and chloroplasts are bound by two membranes (in contrast to other organelles bound by single membrane)
both contain ribosomes
both contain circular DNA
both are autonomous organelles that grow and reproduce within the cell

52
Q

what cells contain mitochondria

A

mitochondria are found in nearly all eukaryotic cells

some cells have one but more often a cell has hundreds

53
Q

How many mitochondria in a cell

A

some cells have only one but most have hundreds or even thousands
how many a cell has depends on its level of metabolic activity

54
Q

describe the membranes of the mitochondria

A

two membranes
each membrane is a phospholipid bilayer
outer membrane is smooth
inner membrane folded called cristae
intermembrane space is the space between the inner and outer membrane
mitochondrial matrix - the compartment enclosed by the inner membrane

55
Q

what is cristae

A

infoldings of the mitochondria

56
Q

what is the inner membrane space

A

the space between the inner and outer membranes of the mitochondria

57
Q

what is the mitochondrial matrix

A

enclosed by the inner membrane of the mitochondria
contains different enzymes
contains mitochondrial DNA and ribosomes
enzymes that function in cellular respiration embedded into the inner membrane

58
Q

why is the cristae folded?

A

gives a larger surface area for cellular respiration

59
Q

what does a chloroplast contain?

A

a chloroplast contains chlorophyll (green pigment) along with enzymes and other molecules that function in photosynthesis

60
Q

where are chloroplasts located

A

in leaves and other green parts of plants and algae

61
Q

describe the structure of a chloroplast

A

two membranes separated by a narrow intermembrane space
inner membranes divide the chloroplast into 3 compartments -
intermembrane space
thylakoids (stacks called granum)
fluid outside the thylakoids called stroma - contains chloroplast DNA and ribosomoes

62
Q

what is a plastid?

A

plant organelle

chloroplast is one kind of plastid

63
Q

describe two characteristics shared by chloroplasts and mitochondria

A

both involved in energy production
both have multiple membranes that separate their interiors into compartments
both have inner membranes that give large surface area - cristae in mitochondria and thylakoids in chloroplasts
both have embedded enzymes

64
Q

Do plant cells have mitochondria?

A

Yes

plant cells are able to make their own sugar by photosynthesis but mitochondria are needed to make ATP

65
Q

are mitochondria and chloroplasts part of the endomembrane system

A

No
different structure to membranes - double membrane for mitochondria and chloroplasts / single for others
not derived from ER

66
Q

what is a peroxisome

A

bound by s single membrane
contain enzymes for metabolism
different functions
cooperate with mitochondria and chloroplasts

67
Q

what is the function of peroxisomes

A

remove hydrogen atoms from various substrates and transfer them to oxygen producing hydrogen peroxide
peroxisoomes contain enzymes that convert hydrogen peroxide to water

68
Q

what structures make up the cytoskeleton?

A

microtubules microfilaments and intermediate filament

69
Q

what are the functions of the cytoskeleton?

A

structural support
maintain shape
provides anchorage for organelles
in some cells facilitates motility - changes in cell location and movement of cell parts

70
Q

what is the structure of microtubules

A

globular proteins called tubulins

microtubules are hollow rods made of tubulin protein subunits

71
Q

describe tubulin

A

hollow tubes

a dimer made from alpha tubulin and beta tubulin

72
Q

what is a dimer

A

a molecule made up of two components

73
Q

what is the function of microtubules

A

shape cell
support cell
tracks along which motor proteins can move - guide vesicles from the ER to Golgi and from golgi to plasma membrane
microtubules are also involved in the separation of chromosomes during cell division
cilia and flagella

74
Q

what is a centrosome?

A

microtubules grow out of the centrosome

located near the nucleus

75
Q

what is a centriole

A

found within the centrosome (where microtubules grow)

nine sets of three microtubules arranged in a ring

76
Q

what is a primary cilium?

A

in vertebrate animals almost all cells have a primary cilium

signal receiving antenna

77
Q

how are cilia and flagella different

A

usually large numbers of cilia (except primary cilium)
usually only one or a few flagella
flagella are longer
different beating pattern

78
Q

what is the structure of cilia and flagella

A

group of microtubules sheathed in an extension of the plasma membrane
9 doublets of microtubules in a ring with 2 in centre (9+2)
anchored by a basal body
dyneins (motor proteins) involved in movement

79
Q

what are microfilaments made from

A

actin (also called actin filaments)

80
Q

what is the role of microfilaments

A

support cell shape (network inside the plasma membrane)

cell motility - allow cell to contract e.g. amoeboid crawling / cytoplasmic streaming in plants

81
Q

what are pseudopodia

A 
some cells (amoeba and white blood cells) move along by crawling movement.  The cell crawls along a surface by extending cellular extensions called pseudopodia and moving towards them
made possible by microfilaments and myosin
82
Q

what is cytoplasmic streaming?

A

in plant cells
circular flow of cytoplasm
made possible by microfilaments
speeds up the movement of organelles and the distribution of materials within the cell

83
Q

what cells have intermediate filaments

A

only the cells of some animals including vertebrates

microtubules and microfilaments found in all eukaryotes

84
Q

what is the role of intermediate filaments

A

play an important role in reinforcing cell shape and fixing the position of organelles (permanent framework for the cell)
sturdy and more permanents than microtubules and microfilaments

85
Q

what brings about cell movement

A

interaction between actin filaments (microfilaments ) and myosin
e.g. muscle cells
amoeba movement (pseudopodia)
cytoplasmic streaming

86
Q

what cells have cell walls

A

this is one feature that distinguishes plant and animal cells
prokaryotes fungi and some unicellular eukaryotes (protists)

87
Q

functions of the cell wall

A

protects the plant cell
maintains its shape
prevents excessive uptake of water
hold the plant upright

88
Q

what are cell walls made from

A

cellulose fibres embedded in other polysaccharides and proteins
in fungi - chitin

89
Q

what is the structure of the cell wall

A

young plant cell secretes a thin and flexible cell wall (around one cell) called the primary cell wall
the primary cell walls of adjacent cells is glued together by the middle lamella (pectins)
when the plant stops growing it strengthens its cell wall by secreting hardening substances

90
Q

what is the middle lamella

A

a layer of sticky polysaccharides (pectins) that glue the cell walls of plant cells together

91
Q

what is the extracellular matrix

A

like the cell wall of animal cells

92
Q

what is the extracellular matrix made of

A

glycoproteins - collagen
proteoglycans

proteins and sugars

93
Q

what are integrins

A

cell surface receptor proteins
built into the plasma membrane
attach to microfilaments of the cytoskeleton
transmit signals between the extracellular matrix and cytoskeleton - can result in changes in cell behaviour

94
Q

what is fibronectin

A

glycoproteins that attach cells to the extracellular matrix
bind to integrins
helps ECM to communicate with cell - mechanical signalling

95
Q

what are plasmodesma

A

perforate cell walls
channels that connect plant cells
cytosol can pass through plasmodesma to other cells
water and some solutes can pass freely from cell to cell

96
Q

what types of cell junctions exist in animal cells

A

tight junctions
desmosomes
gap junctions

97
Q

what are tight junctions

A

plasma membranes of neighbouring cells are bound together by proteins
continuous seal
prevents leakage of extracellular fluid
e.g. skin cells are watertight

98
Q

what are desmosomes

A

like rivets fasten cells together (hinges)

attach muscle cells to each other

99
Q

what are gap junctions

A

found in animal cells
also called communicating junctions
provide cytoplasmic channels from one cell to an adjacent cell (similar to plasmodesma in plants)
allows ions, sugars, amino acids and other small molecules to pass
pores surrounded by membrane proteins
necessary for communication between cells in many types of tissues - heart/muscle/ animal embryos

100
Q

what are membrane proteins and what are their function

A

proteins embedded in the plasma membrane or other cellular membranes
transport substances across membranes
conduct signals
e.g. proton pump / calcium channel / aquaporin

101
Q

Which cells have ribosomes

A

all living organisms have ribosomes
Eukaryotic ribosomes are called 80s ribosomes
Prokaryotic (bacteria/archaea) ribosomes are 70s - smaller
Mitochondria in cells also have ribosomes - these are smaller than those in the cytoplasm and are made separately to them
s - relates to centrifugiing

102
Q

what are cell wall’s made of?

A

primary cell wall - cellulose in a gel like matrix

secondary cell wall - cellulose and polysaccharides

103
Q

which organisms have mitochondria

A

all eukaryotic cells

not in prokaryotes - they don’t have membrane bound organelles

104
Q

what do mitochondria , chloroplasts and nuclei have in common

A

all have functional DNA

Bio1MGC (11 decks)

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