Topic 2A - Cell structure and division DVY * Flashcards
Eukaryotic cells and organelles prokaryotic cells and viruses analysis of cell components cell division - mitosis cell division - investigating mitosis
what are eukaryotic cells?
complex cells which make up animals, plants, algae and fungi
what are prokaryotic cells?
smaller simpler cells, like bacteria, they make single-celled organisms
what are organelles?
parts of cells, each with a specific function
what organelles does an animal cell have? (11)
cell surface membrane/plasma membrane rough ER smooth ER nucleolus nucleus lysosome ribosome nuclear envelope Golgi apparatus cytoplasm mitochondria
what organelles does a plant cell have? (13)
cell surface membrane/ plasma membrane chloroplast rough ER smooth ER plasmodesma mitochondria Golgi apparatus vacuole cytoplasm nucleolus nucleus ribosome cell wall
what organelles do algal cells have?
they have all the same organelles as plant cells
how are fungal cells different to plant cells?
they are the same except their cell walls are made of chitin not cellulose
they don’t have chloroplasts
what are plasmodesmata?
channels within the cell wall for exchanging substances between cells
what is a cell surface membrane?
the membrane found on the surface of animal cells and just inside the cell wall of others. its mainly made of lipids and protein
what is the function of the cell surface membrane?
it regulates the movement of substances out of the cell. it has receptor molecules so it can respond to chemicals like hormones
what is the nucleus?
a large organelle surrounded by a nuclear envelope, it contains chromosomes made from protein-bound linear data, it also has a nucleolus.
what is the nuclear envelope?
a double membrane, which contains many pores, the outer membrane is continuous with the rough ER
what is the function of the nucleus?
it controls the cells activities, DNA contains instructions to make proteins
what is the function of nuclear pores?
they allow substances to move between the nucleus and the cytoplasm
what is the function of the nucleolus?
to make ribosomes
it produces the rRNA used to make the ribosome subunits
what does the nucleus contain?
nucleolus nuclear envelope nuclear pores chromatin nucleoplasm
what is the mitochondria?
oval-shaped organelles with a double membrane, inside of which is the matrix?
what is the cristae?
finger like projections which are formed from the folding of the inner membrane
what does the matrix contain?
enzymes involved in respiration, as well as proteins, lipids and some DNA
what is the function of the mitochondria?
it is the site of aerobic respiration where ATP is produced. found in large numbers in very active cells that require a lot of energy
What is the chloroplast?
a small, flattened structure found in plant and algae cells, surrounded by a double membrane
what does the mitochondria contain?
outer membrane
inner membrane
cristae
matrix
what does a chloroplast contain?
thylakoid membranes Grana lamellae stroma double membrane
what are grana?
stacks of thylakoid membranes, where some parts of photosynthesis take place
what is the lamellae?
thin flat pieces of thylakoid membrane which connect the grana
what is the function of chloroplass?
its the site of photosynthesis.
what is the stroma?
a thick fluid found in chloroplasts where some of the photosynthesis takes part
What is the Golgi apparatus?
a group of fluid filled, membrane-bound flattened sacs. vesicles are seen at the edge of these sacs
what is the function of the Golgi apparatus?
it processes and packages new lipids and proteins. it also makes lysosomes
What is chromatin?
the loose form that DNA takes when the cell is not dividing. it stains well so the nucleus can be easily identified
what is a Golgi vesicle?
a small fluid-filled sac in the cytoplasm surrounded by a membrane. its produced by the Golgi apparatus
what is the function of a Golgi vesicle?
it stores lipids and proteins made by the apparatus and transports them out of the cell
what is a lysosome?
a round organelle surrounded by a membrane. it has no clear internal structure
its a type of Golgi vesicle
what does a lysosome contain?
digestive enzymes called lysozymes, that are kept separate from the cytoplasm by the membrane
what is the function of the enzymes in the lysosome?
to digest invading cells or to break down worn out components of the cell
what is a ribosome?
very small organelle that floats freely in cytoplasm or is attached to the rough ER
what is a ribosome made from?
its made up of proteins and RNA which aren’t surrounded by a membrane. it has a small and large subunit
what is the function of a ribosome?
the site of protein synthesis
what is the rough endoplasmic reticulum?
a system of membranes enclosing a fluid-filled space. the surface is covered in ribosomes
what is the function of the rough endoplasmic reticulum?
it folds and processes proteins that have been made at the ribosomes
what is the smooth endoplasmic reticulum?
a system of membranes enclosing a fluid-filled space. with no ribosomes attached
what is the function of the smooth endoplasmic reticulum?
it synthesises and processes lipids
what is the cell wall?
rigid structure that surrounds cells in plants, algae and fungi. in plants and algae its mostly cellulose in fungi its made of chitin
what is the function of a cell wall?
to support cells and prevent them from changing shape
what is a cell vacuole?
membrane-bound organelle found in cytoplasm of plant cells. its surrounding membrane is called the tonoplast
what does the vacuole contain?
cell sap - a weak solution of sugars and salts
what is the function of the vacuole?
helps maintain pressure inside cell, keeping the cell rigid, so plant doesn’t wilt.
involved in isolation of unwanted chemicals inside the cell
what is the structure of epithelial cells?
walls of the small intestine have lots of finger-like projections called villi
epithelial cells on the surface of villi have folds in their cell membrane called microvilli
have lots of mitochondria
how are epithelial cells in the small intestine specialised to absorb food efficiently?
villi and microvilli - increase surface area for the absorption of food
mitochondria - provide energy for transport of digested food molecules into the cell
how are organ systems formed?
specialised cells group together to form tissues that work together to form a particular function
different tissues work together to form organs
different organs make up an organ system
example of an organ system being formed:
epithelial cells make epithelial tissue
epithelial tissue, muscular tissue and glandular tissue form the stomach
stomach is part of the digestive system
what organelles does a prokaryotic cell have?
cytoplasm plasma membrane cell wall flagellum capsule plasmids DNA
what is the cytoplasm in a prokaryotic cell?
it has no membrane bound organelles, it has (70s) ribosomes but they’re smaller than the ones in a eukaryotic cell
what is the function of the plasma membrane in a prokaryotic cell?
mainly made of lipids and proteins. it controls the movement of substances into and out of the cell
what is the cell wall in a prokaryotic cell?
it supports the cell and prevents it from changing shape. its made of a polymer called murein
what is the flagellum in a prokaryotic cell?
a long, hair-like structure that rotates to make the cell move. not all have one, some have many
what is the function of the capsule in a prokaryotic cell?
made up of secreted slime. it helps protect bacteria from attacking cells of the immune system. not all have one
what is the plasmids in a prokaryotic cell?
small loops of DNA that aren’t part of the main circular DNA molecule. they can be passed between prokaryotes. not all have one some have many
what is the DNA in a prokaryotic cell?
prokaryotic cells have no nucleus. DNA floats free in the cytoplasm. it’s circular DNA that is seen as 1 long coiled up strand. it’s not attached to any histone proteins
what is murein?
a glycoprotein, which is a protein with a carbohydrate attached
what do plasmids contain?
genes for things like antibiotic resistance
what are viruses?
nucleic acids surrounded by protein, they are acellular
how do viruses compare to bacteria?
they’re smaller
they have no plasma membrane, no cytoplasm and no ribosomes
what do all viruses do?
invade and reproduce inside the cells of other organisms. these cells are known as host cells
what do viruses contain?
a core of genetic material (DNA or RNA) capsid - protein coat around the core attachment proteins stick out from the edge of the capsid lipid envelope reverse transcriptase enzyme matrix
what do attachment proteins do in viruses?
let the virus cling on to a suitable host cell
how do prokaryotic cells replicate?
binary fission
what are the steps of binary fission?
- circular DNA and plasmids replicate.
- cell gets bigger, DNA loops move to opposite poles of cell
- cytoplasm begins to divide, new cell walls begin to form
- cytoplasm divides, 2 daughter cells are produced, each with a copy of circular DNA and variable number of plasmids
how many times can a prokaryotic cells genetic material replicate?
DNA loop - once
plasmids - many times
what are the steps of virus replication?
- attachment proteins bind to complementary receptor proteins on surface of host
- inject DNA or RNA into the host cell - the host cell uses its own machinery to replicate the viral particles
why can certain viruses only affect certain cells?
different viruses have different attachment proteins, so require different receptor proteins on host cells
what is magnification?
how much bigger the image is than the specimen
what is the calculation for magnification?
size of image/ size of real object
both must be measured in the same units
what is resolution?
how detailed an image is. how well a microscope distinguishes between 2 points that are close together
what are the 2 main types of microscope?
optical and electron
how do optical (light) microscopes form an image?
using light and lenses to focus this light on the specimen
what is the resolution of an optical microscope?
its max resolution is 0.2 micrometres
so they can’t be used to view organelles smaller than this like ribosomes, the ER and lysosomes
what is the maximum magnification of an optical microscope?
x 1,500
how do electron microscopes form an image?
they use electrons
what is the max resolution of an electron microscope?
0.0002 micrometres, much higher than an optical microscope (about 1000 times) to give more detailed images
what is the maximum magnification of an electron microscope?
x1,500,000
what are the 2 types of electron microscope?
scanning or transmission
how do transmission electron microscopes work?
use electromagnets to focus a beam of electrons, which is transmitted through the specimen
denser parts of the specimen absorb more electrons, so they appear darker
advantages of TEM:
give high resolution images to see the internal structure of organelles like chloroplasts
high magnification
disadvantages of TEM:
specimen must be thin expensive samples must be dead no "true colour" artefacts may form from staining process training required
how do scanning electron microscopes work?
they scan a beam of electrons across the specimen. this knocks electrons off the specimen which are gathered in a cathode ray tube to form an image
what are the advantages of SEM?
surface of specimen can be seen, 3D images produced specimen can be thick high resolution high magnification
how to prepare a ‘temporary mount’ of a specimen on a slide:
pipette small drop of water on to the slide
use tweezers to place thin section of specimen on top
add drop of a stain
add cover slip
what is the slide?
a strip of clear glass or plastic
what are stains used for?
to highlight objects in a cell. e.g. eosin for cytoplasm, potassium iodide solution for starch grains
what is a cover slip?
a square of clear plastic that protects the specimen
how to place a cover slip:
stand slip upright on slide and carefully tilt and lower so it covers specimen, avoid trapping air bubbles
what do epithelial tissues do?
line the surface of organs, protect, have secretary functions
what do connective tissues do?
made from fibroblasts that can produce collagen fibres
support - holds together other tissues
provides strength and elasticity
what is muscle tissue used for?
movement
what do xylem tissues do?
tubes formed from dead, hollow xylem cells
transport water from roots to leaves
transport mineral salts
provides mechanical support
what is palisade mesophyll tissue?
photosynthetic tissue made from leaf palisade mesophyll cells. they carry out photosynthesis
what is spongy mesophyll tissue?
tissue made from spongy palisade mesophyll cells.
they provide a large surface area for gas exchange via diffusion
what does epidermal tissue (epidermis) do?
protects leaf
allows gaseous diffusion
what are the advantages of optical microscopes?
easy to use
cheap (
what are the disadvantages of optical microscopes?
low resolution due to long wavelength of light
low magnification
thin specimen needed
why is a thin specimen bad?
may be bad representation of the specimen
disadvantages of SEM:
give lower resolution images than TEM's expensive training required samples must be dead no "true colour"
how can you separate organelles from a cell?
using cell fractionation
what are the steps of cell fractionation?
homogenisation
filtration
ultracentrifugation
what is homogenisation?
breaking up the cells e.g. by vibrating them or grinding them in a blender
what is filtration?
getting rid of the unwanted bits
what is ultracentrifugation?
separating the organelles from the solution containing a mixture of organelles
what does homogenisation do?
breaks up the plasma membrane and releases the organelles into the solution
what must a solution be in order to be homogenised?
ice-cold
isotonic
buffered
why must a solution be ice-cold in order to be homogenised?
to reduce the activity of enzymes that break down organelles
why must a solution be isotonic in order to be homogenised?
it must have the same concentration of chemicals as the cells being broken down to prevent damage to the organelles through osmosis
why must a solution be buffered in order to be homogenised?
prevents pH fluctuating so enzyme or organelle structures aren’t affected
what happens during filtration in cell fractionation?
homogenised cell solution is filtered through a gauze to separate large debris or tissue debris, like connective tissue, from the organelles. the organelles are much smaller than the debris, so they pass through the gauze
what is the 1st step of ultracentrifugation?
cell fragments are poured into a tube. tube is put in a centrifuge and spun at low speed. heaviest organelles get flung to bottom of tube and forming the pellet at bottom, the rest of the organelles are suspended in the fluid above the sediment (supernatant). the supernatant is drained and spun again, this process is repeated
what is the order of organelles that form a pellet in ultracentrifugation?
they are separated out in order of mass: nuclei chloroplasts mitochondria lysosomes ER ribosomes
What are the 2 types of cell division in eukaryotes?
mitosis
meiosis
what is mitosis?
cell division that produces genetically identical cells
what happens in mitosis?
a parent cell divides to produce 2 genetically identical daughter cells. (they contain an exact copy of the DNA of the parent cell)
what is mitosis needed for?
the growth of multicellular organisms and repairing damaged tissues
what does the cell cycle consist of?
a period of cell growth and DNA replication called interphase. mitosis happens after that
what is interphase subdivided into?
G1, S and G2
what is G1 in interphase?
gap phase 1 - cell grows and new organelles and proteins are made
what is S in interphase?
synthesis - cell replicates its DNA, ready to divide by mitosis
what is G2 in interphase?
gap phase 2 - cell keeps growing and proteins needed for cell division are made
what happens during interphase?
the cell carries out normal functions, but also prepares to divide. The cell’s DNA is unravelled and replicated. The organelles are also replicated, and its ATP content is increased
why is the cell’s DNA unravelled and replicated during interphase?
to double it’s genetic content
why are the organelles replicated during interphase?
so it has spare ones
why is the ATP content increased during interphase?
ATP provides the energy needed for cell division
what are the four division stages of mitosis?
prophase
metaphase
anaphase
telophase
what are centrioles?
tiny bundles of prottein
what happens during prophase?
chromosomes condense, getting shorter and fatter.
centrioles start moving to opposite ends of the cell, forming spindles. nuclear envelope breaks down and chromosomes lie free in the cytoplasm
what is a spindle?
a network of protein fibres
What is the structure of chromosomes as mitosis begins?
made of 2 strands (chromatids) joined in the middle by a centromere.
why are chromosomes made of 2 chromatids as mitosis begins?
each chromosome has already made an identical copy of itself during interphase.
when mitosis is over, the chromatids end up as 1-strand chromosomes in the daughter cells
what happens during metaphase?
the chromosomes line up along the equator of the cell and become attached to the spindle by their centromere
What happens during anaphase?
the centromeres divide, separating each pair of sister chromatids. the spindles contract, pulling chromatids to opposite poles of the spindle
why do the chromatids appear v-shaped during anaphase?
they are pulled centromere first to opposite poles of spindle
what happens during telophase?
chromatids reach opposite poles on the spindle. they uncoil and become long and thin again. they’re now called chromosomes again. a nuclear envelope forms around each group of chromosomes, so there are now 2 nuclei
what happens after telophase?
cytokinesis
what happens in cytokinesis?
the cytoplasm divides and there are now 2 daughter cells. that are genetically identical to each other and the original cell.
how can you calculate the time that cells spend in a phase?
find the number of cells in that phase as a fraction of the total number of cells and then multiply this by how long a complete cell cycle takes, in minutes
how are tumours formed?
if there’s a mutation in a gene that controls cell division, the cells can grow out of control.
they keep on dividing to make more and more cells, which form a tumour
when does cell division stop?
mitosis and the cell cycle are controlled by genes, when cells have divided enough times to make enough new cells, they stop
what is cancer?
a tumour that invades surrounding tissue
what are some treatments for cancer designed to do?
to control the rate of cell division in tumour cells by disrupting the cell cycle. this kills the tumour cells
what is the down side of treating cancer by disrupting the cell cycle?
they don’t distinguish tumour cells from normal cells. so also kill normal body cells that are dividing
if cancer treatments kill normal cells, how do they work?
tumour cells divide much more frequently than normal cells, so the treatments are more likely to kill tumour cells
what are some cell cycle targets of cancer treatments?
G1 (cell growth and protein production) S phase (DNA replication)
what happens in the G1 cancer treatment?
some chemical drugs (chemotherapy) prevent the synthesis of enzymes needed for DNA replication.
if these aren’t produced, the cell is unable to enter the synthesis phase, disrupting the cell cycle and forcing the cell to kill itself
what happens in the S phase cancer treatment?
radiation and some drugs damage DNA. in the cells cycle DNA in the cell is checked for damage. if severe damage is detected, the cell will kill itself - preventing further tumour growth
what is the practical for investigating mitosis?
root tips can be stained and squashed
what safety precautions should be taken when staining root tips?
safety goggles, lab coat, gloves
what happens in the investigation of mitosis using root tips?
- cut 1cm from the tip of a growing root
- prepare boiling tube containing 1 M HCl acid and put it in a water bath at 60*C
- transfer root tip into boiling tube and incubate for 5 mins
- use pipette to rinse root tip with cold water, then leave to dry
- place root tip on slide and cut 2mm from very tip
- use mounted needle to break the tip open and spread cells out thinly
- add a few drops of stain and leave to soak
- place cover slip over cells and press firmly to squash tissue
- now all the stages of mitosis can be observed under an optical microscope
why is only the tip of a root used in the mitosis practical?
the tip is where growth occurs (so where mitosis takes place)
what does the stain do in an investigation for mitosis?
it will make the chromosomes easier to see under a microscope
what are some examples of stains that can be used in the investigation for mitosis?
toluidine blue O
ethano-orcein
feulgen stain
why is the root tip tissue squashed in the investigation for mitosis?
it will make the tissue thinner and allow light to pass through it. don’t smear the cover slip sideways or the chromosomes will be damaged
what must you do when drawing cells undergoing mitosis?
write down the magnification and label the diagram
what are the steps of observing cells using an optical microscope?
- clip prepared slide onto the stage
- select lowest-powered objective lens
- use coarse adjustment knob to bring stage up to objective lens
- look down eyepiece, use coarse adjustment knob to move stage downwards, until its in focus
- adjust focus with fine adjustment knob, until image is clear
- if greater magnification is needed, swap to higher-powered objective lens and refocus
label an image of a microscope:
PIC
what is the equation for finding the mitotic index?
number of cells visible chromosomes / total number of cells observed
what does the mitotic index let you work out?
how quickly the tissue is growing.
what does a high mitotic index mean?
a plant root tip is constantly growing so you’d expect a high mitotic index.
in other cells it might mean tissue repair is taking place or there is cancerous growth taking place
what is an eyepiece graticule?
its fitted onto an eyepiece, its like a transparent ruler with numbers but no units
what is a stage micrometer?
its placed on the stage. it is a microscope slide with an accurate scale(with units), used to work out the value of the divisions on the eyepiece graticule at a particular magnification
what is an example of how an eyepiece graticule and a stage micrometer work together?
- line up eyepiece graticule and stage micrometer
- each division on the stage is 0.1 mm long
- at this magnification, 1 division on the stage micrometer is the same as 4.5 divisions on the eyepiece graticule
- to work out the size of one division on the eyepiece graticule divide 0.1 by 4.5 = 0.022mm
- so if you look at a cell and its 4 eyepiece divisions long its 0.088mm
what is the formula for working the actual size of a cell through a microscope?
actual size = size of image / magnification
what are artefacts?
things that you can see down the microscope which aren’t part of the cell or specimen
what can an artefact be?
dust, air bubbles, fingerprints or inaccuracies caused by squashing and staining
when are artefacts made?
during the preparation of your slides and shouldn’t be there. slide must be prepared carefully to avoid this
when are artefacts especially common?
in electron micrographs
why are artefacts more common in electron micrographs?
specimens need lots of preparation before they can be viewed under an electron microscope
how did early scientists distinguish between artefacts and organelles ?
by repeatedly preparing specimens in different ways. if an object could be seen with 1 preparation technique but not another, its more likely to be an artefact
