cell structure A Flashcards
define the term prokaryotic cell
DNA is”free” in cytoplasm, no organelles eg// bacteria and and archaea
define the term eukaryotic cell
DNA is contained in a nucleus, contains membrane-bound specialised organelles
what are organelles?
parts that the cells are composed of
describe the structure of the cell surface membrane
-“fluid mosaic” phospholipid bilayer with proteins embedded
function of the cell surface membrane
-isolates cytoplasm from extracellular environment
-selectively permeable to regulate transport of substances
-involved in cell signalling/ cell recognition
describe the structure of nucleus
-surrounded by nuclear envelope, a semi-permeable double membrane
-nuclear pores allow substances to enters/exit
-dense nucleolus made of RNA and proteins assembles ribosomes
function of the nucleus
-controls the cells activities
-pores allow substances to move between the nucleus and then cytoplasm
-nucleolus makes ribosomes
describe the structure of a mitochondrion
-cristae: site of electron transport chain
-matrix: contains enzymes involved in respiration
function of a mitochondrion
-site of aerobic respiration which produces ATP
describe the structure of chloroplasts
-thylakoids which are flattened discs that stack to form
-grana which are linked together by
-lamellae
-stroma which is a fluid filled matrix
function of chloroplasts
site where photosynthesis takes place
describe the structure of Golgi apparatus
-group of fluid-filled membrane bound flattened sacs
-vesicles are often seen at edges of the sacs
function of golgi apparatus
-processes and packages new lipids and proteins
-makes lysosomes
describe the structure of golgi vesicle
-small fluid-filled sac in the cytoplasm
function of golgi vesicle
-stores lipids and proteins made by Golgi apparatus and transports them out the cell
describe the structure of lysosome
-round organelle surrounded by a membrane with no clear internal structure
function of lysosomes
-contain digestive enzymes called lysozymes
-can be used to digest invading cells or to break down worn out components of the cell
describe the structure of rough endoplasmic reticulum
-system of membranes enclosing a fluid filled space
-surface is covered with ribosomes
function of RER
-fold and processes proteins that have been made at the ribosomes
describe the structure of ribosome
small organelle that floats free in cytoplasm or attached to RER
function of ribosomes
-protein synthesis
describe the structure of smooth endoplasmic reticulum
-system of membranes enclosing a fluid filled space
-but no ribosomes
function of SER
synthesises and processes lipids
describe the structure of cell wall
-rigid structure mainly made of carbohydrate cellulose
function the cell wall
supports cells and prevents them from changing shape
describe structure of the cell vacuole
-contains cell sap
-surrounding membrane is called tonoplast
function of cell vacuole
maintain pressure inside the cell and keeps the cell rigid
what are the similarities between eukaryotic and prokaryotic cells?
both have:
-cell membrane
-cytoplasm
-ribosomes
contrast eukaryotic and prokaryotic cells
prokaryotic:
-small cells and unicellular
-no nucleus
-small ribosomes
-replicate through binary fission
-circular DNA
eukaryotic:
-larger cells and often multicellular
-nucleus
-larger ribosomes
-replicate through mitosis
-linear chromosomes associated with histones
describe the process of binary fission
1-circular DNA and plasmids replicate
2-cell gets bigger and DNA loops move to opposite poles of the cell
3-cytoplasm begins to divide
4-cytoplasm divides and two daughter cells are produced
why are viruses referred to as particles instead of cells?
acellular and non living : no cytoplasm,cannot self reproduce, no metabolism
describe the structure of viral particle
-linear genetic material (DNA or RNA)
-surrounded by capsid (protein coat)
-no cytoplasm
-attachment proteins
state the role of attachment proteins on viral particles
enable viral particle to bind to complementary sites on host cell
describe the viral replication process
1.virus attaches to host cell receptor proteins
2.genetic material is released into host cell
3.genetic material and proteins are replicated by host cell “machinery”
4.viral components assemble
5.replicated viruses released from host cell
what are the two types of microscopes?
light/optical and electron microscope
describe how optical microscopes work
1-lenses focus rays of light and magnify the view of a thin slice of specimen
2-different structures absorb different amounts and wavelengths of light
3-reflected light is transmitted to the observer via the objective lens and eyepiece
Suggest the advantages and limitations of using an optical microscope.
+ colour image
+ can show living structures + affordable apparatus
- 2D image
- lower resolution than electron microscopes = cannot see ultrastructure
Describe how a transmission electron microscope (TEM) works.
- Pass a high energy beam of electrons through thin slice of specimen.
- More dense structures appear darker since they absorb more electrons.
- Focus image onto fluorescent screen or photographic plate using magnetic lenses.
Suggest the advantages and limitations of using a TEM.
+ electrons have shorter wavelength than light = high resolution, so ultrastructure visible + high magnification (× 500000)
- 2D image
- requires a vacuum = cannot show living structures
- extensive preparation may introduce artefacts
- no colour image
Describe how a scanning electron microscope (SEM) works.
- Focus a beam of electrons onto a specimen’s surface using electromagnetic lenses.
- Reflected electrons hit a collecting device and are amplified to produce an image on a photographic plate.
Suggest the advantages and limitations of using an SEM.
+ 3D image
+ electrons have shorter wavelength than light = high resolution
- requires a vacuum = cannot show living structures
- no colour image
- only shows outer surface
Define magnification and resolution.
-Magnification: factor by which the image is larger than the actual specimen.
-Resolution: smallest separation distance at which 2 separate structures can be distinguished from one another.
Explain how to use an eyepiece graticule and stage micrometer to measure the size of a structure.
- Place micrometer on stage to calibrate eyepiece graticule.
- Line up scales on graticule and micrometer. Count how many graticule divisions are in 100um on the micrometer.
- Length of 1 eyepiece division = 100mm / number of
divisions - Use calibrated values to calculate actual length of structures.
State an equation to calculate the actual size of a structure from microscopy.
actual size= image size/ magnification
Outline what happens during cell fractionation and ultracentrifugation.
- Mince and homogenize tissue to break open cells & release organelles.
2.Place in a cold, isotonic, buffered solution - Filter homogenate to remove debris.e.g. whole cells
- Perform ultracentrifugation:
a) Spin homogenate in centrifuge.
b) The most dense organelles in the mixture form a pellet.
c) Filter off the supernatant and spin again at a higher speed.
State the order of sedimentation of organelles during differential centrifugation.
most dense -> least dense
nucleus -> mitochondria -> lysosomes ->RER -> plasma membrane -› SER -> ribosomes
Explain why fractionated cells are kept in a cold, buffered, isotonic solution.
-cold: to reduce enzyme activity so that organelles aren’t broken down/damaged
-buffered: maintain constant pH so that enzymes don’t denature
-isotonic: so water doesn’t movie in or out of organelles by osmosis so they don’t burst
State what the cell cycle is and outline its stages.
cycle of division with intermediate growth periods
- interphase
- mitosis or meiosis (nuclear division)
- cytokinesis (cytoplasmic division)
Explain why the cell cycle does not occur in some cells.
After differentiation, some types of cell in multicellular organisms (e.g. neurons) no longer have the ability to divide.
What is the difference between the cell cycle and mitosis?
Cell cycle includes growth period between divisions; mitosis is only 10% of the cycle & refers only to nuclear division.
Outline what happens during interphase.
G1: cell synthesises proteins for replication e.g.cell size doubles replicate protein
S: DNA replicates = chromosomes consist of 2 sister chromatids joined at a centromere
G2: organelles divide
State the purpose of mitosis.
● Growth of multicellular organisms by increasing cell number
● Replacing cells to repair damaged tissues
● Asexual reproduction
Name the stages of mitosis.
- Prophase
- Metaphase
- Anaphase
- Telophase
Outline what happens during prophase.
- chromatin coils and condenses to form chromosomes
- nuclear envelope breaks down
- nucleolus breaks down
- centrioles move to poles of the cell
- centrioles produce spindle fibres
Outline what happens during metaphase.
- spindle fibres attach to centromeres
- chromosomes line up on equator of the cell
Outline what happens during anaphase.
requires energy from ATP hydrolysis
- chromosomes are pulled apart at the centromere by spindle fibres
- then the chromosomes move to opposite poles of the cell (Evidence: v shape)
Outline what happens during telophase.
- chromosomes detach from spindle fibres
- spindle fibres disappear
- chromosomes uncoil and become chromatin
- nucleolus reforms
- nuclear envelope reforms
describe how you would determine a reliable mitotic index from tissue observed with an optical microscope
1.count cells in mitosis in field of view
2.divide this by total number of cells in field of view
3.repeat many times
Name 2 dyes that bind to chromosomes.
• toluidine blue (blue)
• acetic orcein (purple-red)
Suggest how cancer treatments control the rate of cell division.
Disrupt the cell cycle:
• prevent DNA replication
• disrupt spindle formation = inhibit metaphase /anaphase
NB: can also damage healthy cells
Describe how tumours and cancers form
● Mutations in DNA / genes controlling mitosis can lead to uncontrolled cell division
● Tumour formed if this results in mass of abnormal cells
○ Malignant tumour = cancerous, can spread (metastasis)
○ Benign tumours = non-cancerous
