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structure and function of the cell - Coggle Diagram
structure and function of the cell
introduction to the cell
everything is made of cells
pre 1600s no one knew about cells as they're too small to be seen by the naked eye
invention of microscope enabled Robert Hooke (1665) and Anton van Leuwenhoek (1675) to see and draw the first cells
the idea of cells making up everything alive was put forward in 1840 and Cell Theory was created in 1855 contradicting previous 'Spontaneous Generation'
Cell diversity
- size, shape, internal organisation - body contains 10^13 to 10^14 cells of
approx.
300 types in 4 broad groups
Cell size
some cells are large enough to be seen unassisted such as the human ovum
most cells are small because
1.
the cell's nucleus can only control a certain volume of active cytoplasm
2.
cells are limited in size by their surface area to volume ratio
a group of cells has a relatively larger surface area than a single cell of the same volume
nutrients, oxygen, and other necessary materials must enter through the surface
as a cell grows larger at some point its surface area becomes too small to allow these materials to enter the cell quickly enough to meet the cell's need -
Fick's Law
rate of diffusion
a
surface area
x
concentration difference
distance
.
Cell shape
- cells come in various shapes depending on function
neurones are long and thin
red blood cells are smooth rounded disks
Internal organization
- cells contain a variety of internal structures called
organelles
1.
organelles
are cell components that perform a specific function in that cell
2.
just as the organs of a multicellular organism carry out life functions
3.
there are many different cells but all retain certain common features
5.
the entire cell is surrounded by a thin
cell membrane
- all membranes have the same thickness and basic structure
6.
organelles often have their own membranes - again with a similar structure
7.
the nucleus, mitochondria, and chloroplasts
have double membranes called
envelopes
8.
because membranes are fluid mosaics, the molecules making them up -
phospholipids
and
proteins
- move independently
the proteins appear to float in the
phospholipids bilayer
and thus membranes can be used to transport molecules within the cell e.g.
endoplasmic reticulum
9.
proteins
in the membrane can be used to transport substances across the membrane - e.g. by
facilitated diffusion
or by
active transport
10.
the proteins on the outside of cell membranes identify us as unique
Prokaryotes / Eukaryotes
organisms whose cells normally contain a nucleus
organisms whose cells lack a nucleus and have no membrane-bound organelles
Typically
bacteria
Typically
protoctista, fungi, plants, animals
Typically
~ 1-10 µm
Typically
~ 10-100 µm (sperm cells) apart from the tail, are
smaller)
nuclear body - no nucleus
real nucleus with nuclear envelope
circular DNA (ccc DNA)
70S Ribosomes
very few cytoplasmic structures
flagellae/cilia made of flagellin cell movement
no mitochondria
no chloroplasts
single celled
binary fission (simple cell division)
DNA as linear molecules (chromosomes) with histone proteins
80S Ribosomes
highly structured cytoplasmic structure by membranes and a cytoskeleton
flagellae and cilia made of tubulin cell movement
1-100 (though RBCs have none) mitochondria
chloroplasts in algae and plants
single cells, colonies, higher multicellular organisms with specialized cells
cell divisionas mitosis or meiosis
Parts of the Eukaryotic cell
structures making up a Eukaryotic cell are determined by the specific functions carried out thus there is no
typical
cell. However they generally have 3 main components
The cell membrane
1.
a cell cannot survive if it is totally isolated from its environment - the cell membrane is a complex barrier separating every cell from its external environment
2.
this 'selectively permeable' membrane regulates what passes into and out of the cell
3.
a
fluid mosaic
of proteins floating in a
phospholipid bilayer
4.
functions like a gate, controlling which molecules can enter and leave the cell
5.
controls which substances pass into and out of the cell
carrier proteins
in or on the membrane are specific, only allowing a small group of very similar molecules through
α- glucose
is able to enter; but
β glucose
is not - many molecules cannot cross at all
selectively permeable
6.
the rest is mostly composed of
phospholipid molecules
they have only two fatty acid 'tails' as one has been replaced by a
phosphate group
making the 'head'
7.
the head is charged and therefore polar - the tails are not charged and so non-polar
thus the two ends of the phospholipid molecule have different properties in water
the phosphate head is hydrophillic and so the head will orient itself so that it is as close as possible to water molecules
the fatty acid tails are hydrophobic and so will orient away from water
8.
when in water, phospholipids line up on the surface with their phosphate heads sticking into the water and fatty acid tails pointing up from the surface
9.
cells are bathed in an aqueous environment both sides of the cell membrane are surrounded by water molecules
10.
this causes the phospholipids of the cell membrane to form two layers known as a
phospholipid bilayer
the heads face the watery fluids inside and outside the cell, whilst the fatty acid tails are sandwiched inside the bilayer
11.
the cell membrane is constantly being formed and broken down in living cells
cytoplasm
1.
everything within the cell membrane which is not the nucleus is known as the cytoplasm
2.
cytosol
is the jelly-like mixture in which the other organelles are suspended, so
cytosol = organelles = cytoplasm
organelles
carry out specific functions within the cell
In Eukaryotic cells, most organelles are surrounded by a membrane
but in Prokaryotic cells there are no membrane-bound organelles
fluid mosaic model of cell membranes
1.
membranes are
fluid
and rather viscous - like vegetable oil
2.
the molecules of the cell membrane are always in motion, so phospholipids are able to drift across the membrane, changing places with their neighbour
3.
proteins, both in and on the membrane form a
mosaic
, floating in amongst the phospholipids
4.
because of this, scientists call the modern view of membrane structure the 'fluid mosaic model'
5.
the mosaic of proteins in the cell membrane is constantly changing
membrane proteins
1.
a variety of protein molecules are embedded in the basic phospholipid bilayer
2.
some proteins are attached to the surface of the cell membrane on both the internal and external surface
these may be hormone receptors, enzymes, or cell recognition proteins (or antigens)
3.
other proteins are embedded in the phospholipid bilayer itself. These are often associated with transporting molecules from one side of the membrane to the other and are referred to as
carrier proteins
4.
some of these form channels or pores through which certain substances can pass
(facilitated diffusion)
, whilst others bind to a substance on one side of the membrane and carry it to the other side of the membrane
(active transport)
5.
proteins exposed to the cell's external environment often have carbohydrates attached to them which act as antigens
e.g. blood groups
6.
some viruses may also bind here too
the nucleus
1.
the nucleus is normally the largest organelle within a Eukaryotic cell
2.
Prokaryotes have no nucleus, having a nuclear body instead - this has no membrane and a loop of DNA
3.
the nucleus contains the cell's chromosomes which are normally uncoiled to form a chromatic network, which contain both linear DNA and proteins, known as histones
these proteins coil up at the start of nuclear division, when the chromosomes first become visible
4.
whilst most cells have a single nucleus some cells (macrophages, phloem companion cells) have more than one and fungi have many nuclei in their cytoplasm - they are coenocytic (=common cytoplasm throughout)
5.
the nucleus is surrounded by a
double membrane
called the nuclear envelope, which has many nuclear pores through which mRNA, and proteins can pass. These dimples make it look like a golf ball
6.
most nuclei contain at least one nucleolus (plural, nucleoli). The nucleoli are where ribosomes are synthesised. Ribosomes, you remember, translate mrNA into proteins
7.
when a nucleus prepares to divide, the nucleolus disappears
animal / plant
organelles
nucleolus
rough ER
smooth ER
80S Ribosomes
Cytoskeleton
Golgi apparatus
Cytoplasm
Mitochondria
Vesicles
Vacuoles
Lysosomes
Centrioles
nucleolus
rough ER
smooth ER
80S Ribosomes
Cytoskeleton
Golgi apparatus
Cytoplasm
Mitochondrion
Vesicle
Chloroplast and other plastids
Tonoplast
additional structures
flagellae
plasma membrane
cellulose cell wall
plasmodsmata
mitochondria
found scattered throughout the cytosol, and are relatively large organelles (second only to the nucleus and chloroplasts)
the sites of aerobic respiration, in which energy from organic compounds is transferred to ATP. For this reason they are sometimes referred to as the powerhouse of the cell
ATP is the molecule that most cells use as their main energy currency
Mitochondria are more numerous in cells that have a high energy requirement - our muscle cells contain a large number of mitochondria, as do liver, heart and sperm cells
mitochondria are surrounded by two membranes, indicating that they were once free-living organisms that have become mutualistic and then a part of almost every eukaryotic cell (not RBC's and xylem vessels)
the smooth outer membrane serves as a boundary between the mitochondria and the cytosol
the inner membrane has many long folds, known as cristae, which greatly increase the surface area of the inner membrane, providing more space for ATP synthesis to occur
mitochondria have their own DNA, and new mitochondria arise only when existing ones grow and divide. Thyer are thus semi-autonomous organelles