section 2 cell structure Flashcards
what are cells adapted to do
cells are adapted to perform a particular function. Depending on that function, each cell type has an internal structure that suits it for its job
This structure can be known as ultrastructure
what are some differences with eukaryotic and prokaryotic cells
eukaryotic cells have a distinct nucleus and possess membrane bounded organelles. This differs with prokaryotic cells
what is the best microscope to use in order to see the structures of the organelles within a cell
an electron microscope is the best to use
high resolution
what are some important structures within an eukaryotic cells
Important structures are: 1.nucleus mitochondrion 3.chloroplasts 4.endoplasmic reticulum 5.Golgi apparatus 6.lysosomes 7.ribosomes 8.cell wall 9.vacuoles
(some of these are from plant cells)
what is the nucleus
the nucleus is the most prominent feature of a eukaryotic cell.
The nucleus contains the organisms hereditary material and controls the cell activities
how does the nucleus looks like
the nucleus appearance:
- usually spherical
- between 10 and 20 micrometers in diameter
- has a number of different parts
what is the nucleus function
- the nucleus acts as the control centre of the cell through the production of of mRNA and tRNA (and hence protein synthesis)
- retains the genetic material of the cell in the form of DNA and chromosomes
- manufactures ribosomal RNA and ribosomes
what are the different parts of the nucleus
there are many different parts in the nucleus:
- nuclear envelope
- nuclear pores
- nuclearplasm
- chromosomes
- nucleolus
what is the function of the nuclear pores
they allows the passage of large molecules, such as messenger RNA, out of the nucleus
what are the features of nuclear pores/ how do they look like
There are typically around 3000 pores in each nucleus, each 40-100nm in diameter
(they are around the nucleus)
what are the features of the nuclearplasm/ how do they look like
the nuclearplasm has granular, jelly like material that makes up the bulk of the nucleus (much like the cytoplasm)
what are chromosomes
Chromosomes consists of protein bound, linear DNA
what is the features of the nucleolus/ how do they look like
the nucleolus is the small spherical region within the nucleoplasm
what is the nucleolus function
It manufactures ribosomal RNA and assembles the ribosomes. There may be more than one nucleolus in a nucleus (depends on the cells function).
what is the function mitochondrion
the mitochondrion are the sites of the aerobic stages of respiration.
Therefore responsible for the production of the energy carrier molecule ATP, from the respiratory substrates e.g. glucose
what are respiratory substrates
a respiratory substrate is any organic molecule broken down to release energy for the synthesis of ATP
how do the mitochondria look like
they are usually rod like in shape
around the organelle is a double membrane that controls the entry and exit of material. The inner of the two membranes is folded to form extension known as cristae
what are the features of the cristae/ what are they
cristae are extensions of inner membrane, which in some species extend across the whole width of the mitochondrion.
what is the function of the cristae
they provide a large surface area for the attachment of enzymes and other proteins involved in respiration
what is the matrix
the matrix makes up the remainder of the mitochondrion
what does the matrix contains
it contains:
- proteins
- lipids
- ribosomes
- DNA
what are the chloroplasts
organelles are functions that carry out photosynthesis
how do chloroplasts look like
chloroplasts vary in shape and size but are typically disc shaped
2-10 micrometres and 1 micrometre in diameter
what are the different features of the chloroplasts ( the internal structure)
chloroplast envelope
the grana
the stroma
what is the grana
the grana:
stacks of up to 100 disc - like structures called thylakoids
within the thylakoids is the photosynthetic pigment called chlorophyll
some thylakoids have a tubular extensions that join up with thykaloids in adjacent grana. The grana is where the first stages of photosynthesis (light absorption) takes place
what is the function of the grana
The grana is where the first stages of photosynthesis (light absorption) takes place
what is the stroma
the stroma is a fluid filled matrix where the second stage of photosynthesis takes place (synthesis of sugars)
within the stroma are a number of other structures, such as starch grains
how are chloroplasts adapted to carry out their function ( harvesting sunlight and carrying out photosynthesis
the chloroplast is adapted to carrying out its function:
- granal membranes (part of the grana ) provide a large surface - for attachment of chlorophyll, electron carriers and enzymes that carry out the first stages of photosynthesis
- fluid of stroma possess enzymes for the 2nd stage of photosynthesis
- chloroplast contain both DNA and ribosomes so they can quickly/ easily make some of the proteins needed for photosynthesis
what is an endoplasmic recticulum/ what are its features
(ER) is an eleborate three dimension system of sheet - like membranes, spreading through the cytoplasm of cells
It is continuous with the outer nuclear membrane. The membranes enclose a network of tubules and flattened sacs called cisternae.
what are the two different types of ER
Rough ER
Smooth ER
what are the rough endoplasmic recticulum features
Rough ER features:
has ribosomes present on the outer surface of the membranes
what is the function of the rough endoplasmic recticulum
Rough ER provide a large surface area for the synthesis of proteins and glycoprotiens
provides pathway for the transport of materials (especially proteins, throughout the cell)
what are the features of the smooth endoplasmic reticulum
Smooth ER:
lacks ribosomes on its smooth surface and is often more tubular in appearance
what are the functions of the smooth ER
smooth ER functions:
synthesise , store and transport lipids
synthesise, store and transport carbohydrates
Why do some cells have an extensive amount of ER
cells that therefore manufacture and store large quantities of carbohydrates, protiens and lipids have a very extensive ER
name some cells that require an extensive ER
liver cells
secretory cells
epithelial cells that line the intestines
what is the golgi apparatus
The golgi apparatus occurs in almost all eukaryotic cells and is similar to the SER in structure except that it is more compact
what are the golgi apparatus features
stacks of membranes that make up flattened sacs (cristernae), with small rounded hollow structures called vesicles
what is the function of the golgi apparatus
proteins and lipids produced by ER are passed through the golgi apparatus in a strict sequence.
The golgi apparatus modifies these proteins often adding non - protein components e.g. carbohydrates to them (forms glycoproteins)
the golgi apparatus also labels them, allowing them to be accurately sorted and to be sent their destinations
what happens to the modified proteins and lipids after they are sorted
once sorted, the modified proteins and lipids are transported in golgi vesicles which are regularly pinched off by the ends of the golgi cisternae.
These vesicles may move to the cell surface, where they fuse with the membrane and release their contents to their outer side
what are the other functions of the Golgi apparatus
add carbohydrate to proteins
produce secretory enzymes, such as those secreted by the pancreas
secrete carbohydrates such as those used in making cell walls in plants
transport, modify and store lipids
form lysosomes
what are lysosomes
lysosomes are formed when the vesicles by golgi apparatus contain enzymes such as proteases and lipases
what do lysosomes contain
lysosomes contain:
lysozymes (enzymes that hydrolyse the cell walls of certain bacteria)
many enzymes can be contained within lysosomes (up to 50 enzymes)
how do lysosomes look like
1.0 micrometres in diameter
what are the functions of lysosomes
hydrolyses material ingested by phagoctyic cells, such as white blood cells and bacteria
release enzymes to the outer side of the cell (extocytosis) in order to destroy material around the cell
digest worn out organelle so that the useful useful chemicals they are made of can be re - used
completely break down cells after they have died (autolysis)
where are lysosomes particularly abundant in
given the roles lysosomes perform they are especially abundant in secretory cells
what are microspcopes
microscopes are instruments that produce a magnified image of an object
what kind of lens do light microscopes use
light microscopes use convex lenses
what are the limitations of light microscopes
the relatively long wavelength of light rays mean that a light microscope can only distinguish between two objects if they are 0.2 μm, or further, apart
how can we overcome this limitation of the light microscope
The limitation can be overcome by using beams of electrons rather than light
Beams of electrons have a shorter wavelength than light therefore electron microscopes can be distinguished between two objects only 0.1nm apart
what is resolution
the resolution (or resolving power), of a microscope is the minimum distance apart that two objects can be in order for them to appear as separate items
what does the resolving power (or resolution) of a microscope depend on
the resolving power depends on the wavelength (or form of radiation) used
in a light microscope the resolution is 0.2μm meaning that any two objects which are 0.2μm or more apart will be seen separately (objects close than 0.2μm appear as a single item)
what does greater resolution mean
greater resolution means greater clarity
the image produced is clearer and more precise
what does increasing the magnification do to the resolution
increasing the magnification does not always increase the resolution
Every microscope has a limit of resolution. Up to this point, increasing the magnification will reveal more detail but beyond this point, increasing the magnification will not do this. The object, while appearing larger, will just be more blurred
what is cell fractionation
cell fractionation is the process where cells are broken up and the different organelles are separated out
why is cell fractionation useful
cell fractionation is useful to study the structure and function of the various organelles that make up cells
what must happen before cell fractionation begins
the tissue (the sample) must be placed in a cold, buffered solution of the same water potential of the tissue
why must the solution (in cell fractionation) be cold
to reduce enzyme activity that might break down the organelle
why must the solution (in cell fractionation) be the same water potential of the tissue
to prevent organelles bursting or shrinking as a result of osmotic gain or loss of water
why must the solution (in cell fractionation) be buffered
it must be buffered so that the pH does not fluctuate. Any change in pH could alter the structure of the organelles or affect the functioning of enzymes
what are the two stages of cell fractionation
homogenation
ultracentrifugation
what happens in homogenation
cells are broken up by a homogeniser (blender)
This releases the organelles from the cell. The resultant fluid, known as homogenate, is then filtered to remove any complete cells ad large pieces of debris
what is ultracentrifugation
ultracentrifugation is the process by which the fragments in the filtered homogenate are separated in a machine called a centrifuge. This spins tubes of homogenate at very high speed in orders to create a centrifugal force.
what is the process of ultracentrifugation for animal cells
- The tube of filtrate is placed in the centrifuge and spun at a slow speed
- the heaviest organelles, the nuclei, are forced to the bottom of the tube, where they form a thin sediment or pellet
- The fluid at the top of the tube (supernatant) is removed, leaving just the sediment of the nuclei
- The supernatant is transferred to another tube and spun in the centrifuge at a faster speed than before
- The next heaviest organelles, the mitochondria) are forced to the bottom of the tube
- The process is continued in this way so that, at each increase in speed, the next heaviest organelle is sedimented and separated out
at what speeds are nuclei, mitochondria , lysosomes when separated out during ultracentrifuge
speed of centrifugation/ revolution min-1
nuclei 1,000
mitochondria 3,500
lysosomes 16,500
what are the two main advantages of the electron microscope
- the electron beam has a very short wavelength and the microscope can therefore resolve objects well- it has a high resolving power/resolution
- As electrons are negatively charged the beam can therefore be focused using electromagnets
how many times better are electron microscopes compared to light microscopes
Best modern microscopes can resolve objects that are just 0.1nm apart- 2000 times better than a light microscope
what is a limitation of using an electron microscope
TEM and SEM
Because electrons are absorbed or deflected by molecules in the air, a near-vacuum has to be created within the chamber of an electron microscope for it to work effectively. This means living specimens cannot be observed
a complex “staining” process is required and even then the image is not coloured
the sample must be extremely thin to allow electrons to penetrate (the sample does not need to be extremely thin as electrons do not penetrate for SEM)
image may contain artefacts resulted in the way that the specimen was prepared. This, therefore, means it is not easy to be sure if what we see in the photomicrograph really exists in that form
what are the two different types of electron microscopes
the transmission electron microscope (TEM)
the scanning electron microscope (SEM)
How does the TEM work
TEM consists of an electron gun that produces a beam of electrons that is focused onto the specimen by a condenser electromagnet
Parts of the specimen allow the electrons to pass through and so appear bright. An image is produced on a screen and this can be photographed to give a photomicrograph
how does the TEM work
the beam passes through a thin section of the specimen
Parts of the specimen absorbs electrons and therefore appear dark
other parts of the specimen allow the electrons to pass through and so appear bright
an image is producd on a screen and this can be photograph to give a photomicrograph
what is the resolving power of the TEM
0.1nm although this cannot be achieved in practice because:
difficulties preparing the specimen limit the resolution that can be achieved
a higher energy electron beam is required and this may destroy the specimen
why are the images produced from the TEM 2-D
as the sample is thin, the result is therefore a flat 2-D image
how do we get over the flat 2-D image produced by the TEM
to get over this, we can take a series of sections from the specimen. This can build up a 3-D image of the specimen by looking at the series of photomicrographs produced
This however is a slow and complicated process, the problem has been overcome by the development of the SEM
what is the SEM and how does it work
basically similar to a TEM however it directs a beam of electrons on to the surface of the specimen from above rather than penetrating it form below like the TEM
The beam is then passed back and forth across a portion of the specimen in a regular pattern
electrons are scattered by the specimen- the pattern of the scattering depends on the contours of the specimen surface. This builds up a 3-D image by computer analysis of the pattern of scattered electrons and secondary electrons produced
how can we measure the size of objects using a light microscope
when using a light microscope, we can measure the size of objects, using an eyepiece graticule
what is an eyepiece graticule
it is a glass disc that is placed in the eyepiece of a microscope.
A scale is etched on the glass disc. This scale is typically 10mm long and is divided into 100 sub- division
the scale is visible when looking down the eyepiece of the microscope
why must the eyepiece graticule be calibrated
the scale on the eyepiece graticule cannot be used directly to measure the size of objects under a microscope’s object lens because each objective lens will magnify to a different degree
the graticule must therefore be first calibrated for a particular objective lens. Once calibrated in this way, the graticule can remain in position for future use, provided the same objective lens is used
how do you calibrate the eyepiece graticule
to calibrate an eyepiece graticule, you need to use a special microscope slide called a stage micrometer. This slide also has a scale etched onto it. Usually the scale is 2mm long and its smallest sub divison are 0.1mm (10 micrometers)
how can you calculate the length of divisions on the eyepiece graticule
when the eyepiece scale and stage micrometer scales are lined up it is possible to calculate the length of division on the eyepiece graticule
10 units on the micrometers scale equals to 40 units on the graticule
therefore 1 unit on the micrometer scale equals 4 units on the graticule
as each unit on the micrometer scale equals 10 micrometer, each on the graticule equals 10/4 = 2.5 micrometers
how do we calculate the scale for different objective lenses
by dividing the differences in magnification
e.g. objective lens magnifying x40 gives a calibrating of 25 micrometers per graticule unit
then an objective lens magnifying x400 (10 times greater) will mean a graticule unit is equivalent to 25 micrometers/ 10=2.5 micrometers
what does it mean when we say cells are specialised
in multicellular organisms , cells are specialised to perform specific functions
why are cells specialised
to stay alive, all cells of a multicellular organism perform basic functions
No one cell can provide the best conditions for all functions, therefore, the cells of multicellular organisms are each specialised in different ways to perform a particular role
how are specialised cells formed
each specialised cell has evolved more or fewer of certain organelles and structures to suit the role it carries out
each first group of cells in an embryo are initially identical. As it matures, each cell takes on its own individual characteristics that suit it to the function that it will perform when it mature. In other words, each cell becomes specialised in the structure to suit the role it will carry out
how do genes play a role in specialising cells
all cells in an organism are produced by mitotic division from the fertilised egg. It follows that they all contain the same genes.
The question then arises: HOW THEN DOES THE CELL BECOME SPECIALISED?
every cell contains the genes needed for it to develop into any one of many different cells ( they are stem cells) in an organism. But only some of these genes are switched on (expressed) in any one cell, at any one time. Different genes are switched on in each type of specialised cell. The rest of the genes are switched off.
what are some features that may vary for different specialised cells
shape and number of organelle
it is not just the shape of different cells that varies, but also the numbers of each or their organelles
e.g. a muscle or a sperm cell will have many mitochondria, while a bone cell will have very few
white blood cells have many lysosomes while a muscle cell has very few
why do multicellular organisms function efficiently
cells of a multicellular organism have evolved to become more and more suited to one specialised function and perform it more effectively. As a result the whole organism functions effectively
what are the two ways cell division can take place
mitosis or meiosis
what happens when a cell divides by mitosis
mitosis produces two daughter cells that have the same number of chromosomes as the parent cell and each other
what is mitosis
mitosis is division of a cell that results in each of the daughter cells having an exact copy of the DNA of the parental cell (except in the rare event of a mutation)
The genetic make up of the two daughter nuclei is also identical to that of the parent nucleus
what is the period that always proceeds ( happens before) mitosis
mitosis is always proceeded by a period during which the cell is not dividing. This period is called interphase, a considerable amount of cellular activity takes place including an important event - the replication of DNA
two copies of DNA after replication remain joined together at a place called a centromere
what are the different stages of mitosis
( before mitosis even starts interphase happens)
- propase
- metaphase
- anaphase
- telophase and cytokineses
what happens during prophase
- chromosomes first become visible, initially as long thin threads which later shorten and thicken
- animal cells contain two cylindrical organelles called centrioles, each of which moves to opposite ends (called poles) of the cell
from each of the centrioles, spindle fibres develop, which span the cell from pole to pole
- collectively, these spindle fibres are called spindle apparatus. As plant cells lack centrioles but do develop a spindle apparatus, centrioles are clearly not essential to spindle formation (in plants)
- The nucleolus disappears and the nuclear envelop breaks down, leaving the chromosomes free in the cytoplasm of the cell
- These chromosomes free in the cytoplasm are drawn towards the equator of the cell by the spindle fibres attached to the centromeres
what happens during metaphase
by metaphase the chromosomes are seen to be made up of two chromatids. Each chromatid is an initial copy of the DNA from the parent cell. The chromatids are joined together by the centromere
It is to this centromere that some microtubules from the poles are attached, and the chromosomes are pulled along the spindle apparatus and arrange themselves themselves across the equator of the cell
what happens during anaphase
in anaphase, the centromeres divide into two and the spindle fibres pull the individual chromatids pulling the chromosomes apart
Chromatids move rapidly to their respective, opposite poles of the cell and we now refer to them as chromosomes. The energy for the process is provided by mitochondria, which gather around the spindles. If the cells are treated with chemicals that destroy the spindle, the chromosomes remain at the equator unable to reach the poles
what happens during telophase and cytokineses
In this stage, chromosomes reach their respective poles and become longer and thinner, finally disappearing altogether, leaving only widely spread chromosomes. The spindle fibres disintegrate and nuclear envelope and nucleolus re - form. Finally the cytoplasm divides in a process called cytokineses
What is the nuclear envelope
It is the double membrane that surround
the nucleus
Its outer membrane is continuous with the endoplasmic recticulum of the cell and often has ribosomes on its surface
What is the function of the nuclear envelope
Controls the entry and exit of materials in and out if the nucleus
Controls reactions taking place within nucleus
What are ribosomes
Small cytoplasmic granules found in all cells
They occur in the cytoplasm/accosted with the RER
What are the two types of ribosomes
80s In eukaryotic cells (25 nm in diamete)
70s in prokaryotic cells (mitochondria and chloroplasts are slightly smaller)
What are the features if ribosomes
Ribosomes have two sub units:
One large
One small
Each of which contains ribosmonal RNA a s protein. Despite their small size, they occur in such vast numbers that they can account for 25% of the dry maze of a cell.
What is the function of the ribosomes
Ribosomes are the site of protein synthesis
What is the cell wall made out of
Consists of microfibrils of the polysaccharide cellulose embedded in a matrix
The cellulose microfibrils have considerable strength and so contribute to the overall strength of the cell wall
What are the features of the cell wall
Consists of a number of polysaccharides such as cellulose
Thin layer (middle lamella) this marks the boundary between adjacent cell walls and cements adjacent cells together
What are the of the functions of the cell wall
Provides mechanical strength in order to prevent the cell bursting under pressure created by the osmotic energy of water
To allow water to pass along it and so contribute to the movement of water through the plant
What are the cell walls of algae made up of
Made up of either cellulose/glycoproteins (or a mixture of both)
What are fungi cell walls made up of
It is made up of cellulose but compromise if a mixture of nitrogen containing polysaccharide called chiton, a polysaccharide called glycan and glycoprotein
What are the vaculolea
It is a vacuous filled sac bounded by a single membrane
Within matured plant cells there is usually on large central vacuole
What do vacuole contain
A solution of minerals, salts, sugars, ammo acids, wastes and sometimes pigment such a anthocyanins
What are the functions of the vacuole
Supports herbaceous plants, and herbaceous parts of woody plants by making them turgid
The sugars and amino acids may act as a temporary food store
Pigment e.g. may colour petals which in turn attract pollinating insects
what are tissues
in order for cells to work efficiency, cells are normally aggregated together, this collection of similar cells that perform a specific function is known as a tissue
what is an example of a tissue in an organism
an example of a tissue are epithelial tissues
these are found in animals and consist of sheets of cells. They line the surfaces of organs and often have a protective secretory function
how are zylems specialised for there task/role
zylems occur in plants and is made up of similar cell types. It is used to transport water and mineral ions throughout the plant and also gives mechanical support
what are organs
just as cells are aggregated into tissues, so tissues are aggregrated into organs
an organ is a combination of tissues that are coordinated to perform a variety of functions although they often have one predominant major function. In animals e.g. the stomach is an organ that is involved in the digestion of certain types of food. It is made up of tissues such as
- muscle cells to churn and mix the stomach content
- connective tissue to hold together the other tissues
- epithelium to protect the stomach wall and produce secretions
name an organ in a plant
in plants, a leaf is an organ made up of the following tissues:
- palisade mesophyll made up of leaf palide cells that carry out photosynthesis
- spongy mesophyll adapted for gaseous diffusion
- epidermis to protect the leaf and allow gaseous diffusion
- phloem to transport organic materials away from the leaf
- xylem to transport water and ions into the leaf
how can we determine which structures are organs
it is not easy to determine which structures are organs e.g. blood capillaries are not organs whereas arteries and veins are both organs
- all three have the same major functions ( transport water)
however, capillaries are made up of just one tissue epithelium whereas arteries and veins are made up of many tissues, for example, epithelial, muscle and other tissues
what are organ systems
organs work together as a single unit known as an organ system
The systems may be grouped together to perform particular functions more efficiently. There are a number of organ systems in humans:
respiratory system
digestive systems
circulatory system
what is the structure of bacterial cells
bacteria occur in every habitat in the world
-they are very versatile
-all bacteria possess a cell wall
The cell wall is made up of murein which is a polymer of polysaccharides and polypeptides
- many bacteria further protect themselves by secreting capsule of mucilaginous slime around this wall
- inside cell wall is cell- surface membrane , within which is the cytoplasm that contains 70s ribosomes
- bacteria store food reserves as glycogen granules and oil droplets
- the genetic material in bacteria is in the form of a circular strand of DNA. Separate from this are smaller circular pieces of DNA, called plasmids
why are plasmids useful
plasmids can reproduce themselves independently and may give the bacterium resistance to harmful chemicals, such as antibiotics
plasmids are used extensively as vectors ( carriers of genetic info) in genetic engineering
what are some of the core differences between eukaryotic and prokaryotic cells
prokaryotic cells
- no true nucleus, only an area where DNA is found
- Pro(DNA) is not associated with proteins
- some DNA may be in the form of circular strands called plasmids
- no organelle - bounded organelle
- ribosomes are smaller 70s
- cell wall made of murein
eukaryotic cells
- distinct nucleus, with a nuclear envelope
- DNA is associated with proteins called histones
- There are no plasmids and DNA is linear
- membranes - bound organelles, such as mitochondria, are present
- chloroplasts are present in plants and algae
- ribosomes are larger(80s)
- where present, cell wall is made mostly of cellulose
what are the features of bacteria
cell wall - physical barrier that excludes certain substances and protection against mechanical damage and osmotic lysis
capsule - protects bacterium from other cells and helps groups of bacteria to stick together for further protection
cell surface membrane - acts as a differentially permeable layer, which controls the entry and exit of chemicals
circular DNA - possess the genetic info for the replication of bacterial cell
plasmid - possess genes that may aid the survival of bacteria in adverse conditions, e.g. produces enzymes that break down antibiotics
what are viruses
viruses are cellular, non- living particles. They are smaller than bacteria 20- 300nm
what do viruses contain
contain nucleic acids such as DNA and RNA as genetic material but can only multiply inside living host cells
where is the nucleic acid enclosed
within a protein coat called the capsid
what are some viruses surrounded by
some viruses, like the human immunodeficiency virus, are further surrounded by a lipid envelope. The lipid envelope, or if not present the capsid, have attachment proteins which are essential to allow the virus to identify and attach to a host cell
