Cells Flashcards
Describe the nucleus - structure
Largest organelle, shows darkened patches called chromatin when stained. Surrounded by a nuclear envelope which has nuclear pores. Inside the nucleus is the nucleolus which is a dense body of DNA and RNA used to make rRNA for ribosomal units
What is the function of the nucleus? what are made here?
Contains the cell’s genetic material. Chromatin consists of DNA and proteins, and condenses into visible chromosomes during cell division.
Controls cell division, protein synthesis, codes for enzymes/proteins
RNA and ribosomes are made here.
What is the endoplasmic reticulum made up of? Where are they found?
A series of flattened membrane bound sacs called cisternae. Continuous with the outer nuclear envelope.
what are the two different types of endoplasmic reticulum and how do they differ in appearance?
rough & smooth - rough is studded with ribosomes
What is the function of the rough endoplasmic reticulum?
transports proteins that were made on its attached ribosomes. Some of these proteins will be secreted from the cell
What is the function of the smooth endoplasmic reticulum?
involved in making lipids that the cell needs
Describe the golgi apparatus
consists of a stack of membrane-bound flattened sacs. There may be several within each cell. Not a stable structure - it is constantly changes
What is the function of the golgi apparatus?
modifies proteins produced in the ER and then packages the modified proteins into vesicles for transport. Some modified proteins may be secreted.
Describe the mitochondria
Spherical/sausage shaped. Two membranes separated by fluid filled space. Inner membrane is folded many times to form cristae (increases surface area). The central part is called the matrix. Circular DNA allows them to make their own proteins
What is the function of the mitochondria?
Site of aerobic respiration and ATP (adenosine triphosphate) production
Describe the structure of chloroplasts
Two membranes separated by fluid filled space. Inside the organelle are flattened membrane sacs called thykaloids. A stack of these is called a granum. Chloroplasts often contain starch grains. Loop of DNA and 70s ribosomes
What is the function of chloroplasts?
Site of photosynthesis in plant cells. Light energy drives the reactions of photosynthesis, in which carbohydrate molecules are made from carbon dioxide and water.
Described the structure of lysosomes
Spherical sacs surrounded by a single membrane. Contain powerful hydrolytic enzymes.
What is the function of the lysosomes?
The hydrolytic enzymes inside are used to break down materials eg invading mocroorganisms (phagocytes), or materials surrounding the egg (sperm cells)
Describe the structure of the vacuole
Large central organelle, only found in plant cells. Filled with water and solutes so that it pushes the cytoplasm against the cell wall. Surrounded by the tonoplast.
What is the function of the vacuole?
Makes the cell turgid, helping to support the plant.
What are vesicles? How are they used?
Membrane-bound sacs found throughout cells, used to carry many different substances around the cell.
What are ribosomes and where are they found?
Tiny organelles found in the cytoplasm as well as bound to endoplasmic reticulum. Made up of two subunits.
What do ribosomes do?
Site of protein synthesis in the cell. Act as an assembly line where coded information from the nucleus is used to assemble proteins from amino acids.
What are centrioles and where are they found?
Small tubes of protein fibres (microtubules) there is a pair of them (called a centrosome) next to the nucleus in animal cells and in the cells of some protoctists. Form rings of 9 microtubules
What are cilia and flagella ? What are they made up of?
Hair like extensions which stick out from the surface of the cell. Each one is made up of a cylinder containing nine microtubules arranged in a circle and two microtubules in a central bundle.
How are cilia and flagella able to move?
Using energy from ATP
What is the function of flagella?
Used to move the whole cell
<p>What is the function of cilia? What kind of cells at they found on?</p>
<p>Found on ciliates epithelial cells where their sweeping movements move substances like mucus across the surface of the cells.</p>
What is the cytoskeleton made up of? What is its importance?
The network of protein fibres found inside a cell. Made up of actin and tubulin.
Importance: provides mechanical strength, aids transport within the cell, enables cell movement.
What is the highest poss. magnification of a light microscope? and resolution?`
x1500
200nm
Define magnification
the number of times an object is enlarged
what is resolution?
the clarity of an image- the ability to distinguish between 2 close points
what is an advantage of using a light microscope as opposed to an electron microscope?
living processes, such as movement/cell division, are visible. Cheaper as when using an electron microscope the specimen has to be stained with heavy metals such as gold to prevent electrons from passing through.
maximum magnification of a transmission electron microscope? and resolution?
x300,000
0.5nm resolution
What are the main principles of electron microscopy? (e.g preparation of specimen)
- specimen is finely section e.g. to a few nm thick
- it is stained with heavy metals to prevent electrons from passing through
- specimen supported on a fine mesh grid through which electrons can pass through
- placed in a small chamber in a vacuum to prevent gas molecules scattering the electron beam
- electrons reflected by the specimen are focused using an electromagnet
- an electron micrograph is formed on the screen - black and white
magnification and resolution of a scanning electron micrograph
LEIGHWAY
150,000x
10nm
calculating magnification: magnification =
image size / actual size
describe 3 differences between prokaryotic and eukaryotic cells
prokaryotic: no membrane-bound nucleus, naked DNA (e.g. strand), 70s ribosomes, cell wall always present and made of peptidoglycan, plasmids present
eukaryotic: membrane-bound nucleus, linear DNA, cell wall may be present and made of cellulose/chitin, may have flagellae
what are the function of nuclear pores?
allow substances to exit the nucleus, e.g. mRNA to be synthesised/ribosomal units - but too small to allow DNA to exit (protected)
connects to rough endoplasmic reticulum in some places
Describe briefly to movement of proteins terminating in their secretion?
mRNA leaves nuclear pores, synthesised by ribosomes in the RER, pinched off in a vesicle, moved to Golgi apparatus where they are modified (addition of carbohydrate) and packaged, enclosed in another vesicle, moved through the cytoplasm and fused with the cell membrane to secrete the protein in exocytosis
what is the fluid mosaic model of cell membranes made up of?
phospholipid bilayer (hydrophilic heads made up of glycerol and phosphate group towards extracellular fluid/cytoplasm, 2 hydrophobic fatty acid tails away) containing intrinsic and extrinsic proteins. branched carbohydrate chains attached to some proteins/lipids forming glycoproteins/glycolipids
what is the function of cholesterol in the cell membrane?
regulates the fluidity of the membrane, forces water-soluble materials to pass though intrinsic proteins.
What are the functions of phospholipids in the cell membrane?
form a bilayer. Barriers to water/water-soluble molecules and ions and a passage for lipid soluble molecule such as steroid hormones. Flexibility - can move, break and rejoin
What are the importances of glycoproteins and glycolipids?
- receptor sites for hormones
- receptors for neurotransmitters
- act as antigens in cell recognition
- glycoproteins act as enzymes (!)
- cell adhesion to form tissues
- cell stability - form H bonds with surrounding water molecules to keep the cell in a fixed positionish if needs be
what are 3 functions of cell membranes? within cell & cell surface
- Permeable - control the exit/entry of substances to the cell/organnelle
- compartmentalisation within tissues (individual cells have their own membranes) maintains optimal surface area : volume ratios for maximum uptake of nutrients/expulsion of wastes
- compartmentalisation within cells (membrane-bound organnelles) - nuclear membrane protects DNA from enzymes in cytoplasm, hydrolytic enzymes contained in lysosomes protects rest of cell from its hydrolases and acidic pH. Allow specific different reactions within the cell to be isolated from each other.
- some are folded (e.g. microvilli) to increase surface area in specialised cells
- cell signalling thanks to glycoproteins
- site for attachment of enzymes
describe diffusion of materials across the cell membranes
the passive movement of small molecules from a region of high concentration to one of low concentration down a concentration gradient.
Passive - no ATP requires.
Results in an equilibrium - equal conc. of substance either side of the membrane
describe facilitated diffusion across the cell membrane
The passive movement of large molecules/charged ions through specific channel proteins in membranes.
These materials cannot pass through the hydrophobic phospholipid tails.
Describe osmosis across cell membranes
passive movement of water from a region of higher water potential to one of lower water potential through a partially permeable membrane - down a water potential gradient. Water can move through the phospholipid bilayer or in larger quantities via aquaporin proteins in the cell membrane
what is the effect of solutes dissolved in water on its water potential? what is the water potential of pure water?
Solutes dissolved in the water lower its water potential as they are charged and attract water molecules. Pure water is given a water potential of 0.
What happens when animal cells are placed in a solution of lower water potential? and plant cells?
animal cells will lose water and shrink, plant cells will lose water and the cell becomes plasmolysed - the cell membrane shrinks away from the cell wall
what happens when animal cells are placed in a solution of higher water potential? and plants?
animal cells will gain water, swell and burst (lysed). Plant cells not rupture with excess water thanks to their cell walls - they are incapable of unlimited expansion, and are turgid and rigid when fell of water - contributing to the support of the plant.
Describe active transport of materials across the cell membrane
The movement of molecules or ions against a concentration gradient e.g. low to high conc.
ATP required to open up the relevant transporter proteins in the cell membrane, allowing them to bind to the molecule or ion.
Describe endocytosis across cell surface membranes
The uptake of particles that are too large to pass through the cell membrane/bulk transport.
Phagocytosis - uptake of particles, pinocytosis - uptake of liquids.
ATP required - membrane extends around the particle/liquid and fuse together to form a membrane-bound vacuole, the contents of which are digested via hydrolyses in a lysosome.
describe exocytosis across cell membranes
secretion of large materials/bulk from the cell.
Secretory materials are formed in the RER and/or the golgi bodies and are packaged into secretory vesicles, which fuse with the cell surface membrane releasing their contents to the outside.
Requires ATP.
Effect of high temperatures on membrane permeability:
Increased permeability as:
- more kinetic energy causes phospholipids to vibrate
- gaps form between them
- protein channels also vibrate - tertiary structure may unravel, changing their shapes and leaving gaps
- gaps mean larger molecules can pass through
Effect of low temperatures on membrane permeability:
Decreased permeability as:
- less kinetic energy so phospholipids and proteins pack together more tightly leaving smaller gaps between them
- molecules and ions move more slowly
- respiration is slower, so less ATP is made
- meaning less active transport, endocytosis and exocytosis
- molecules and ions move more slowly
Effect of low temperatures on membrane permeability:
Decreased permeability as:
- less kinetic energy so phospholipids and proteins pack together more tightly leaving smaller gaps between them
- molecules and ions move more slowly
- respiration is slower, so less ATP is made
- meaning less active transport, endocytosis and exocytosis
- molecules and ions move more slowly
Describe normal body cells in terms of their chromosomes
Diploid - have two sets of chromosomes, one set of 23 from each parent so a total of 46
These CAN be (not in mitosis) arranged in homologous pairs which are the same shape and size and carry the same typed of genes. Homologous pairing occurs in meiosis.
What is mitosis used for and why?
growth, repair and asexual reproduction - produces genetically identical cells
What is different about meiosis compared to mitosis?
- type of cell division that halves the chromosome number from diploid to haploid
- produces genetically varied cells
- homologous pairs form
- used for sexual reproduction to form gametes
What is the order of stages in mitosis?
Prophase, metaphase, anaphase, telophase.
Interphase is NOT part of mitosis
Describe what happens during interphase
- DNA replication occurs forming 2 identical chromatids
- organnelles replicate
- build up of ATP
- protein synthesis
- growth of cell
Describe main events during early and late prophase:
Early:
- chromosomes condense and supercoil - now visible
- DNA condenses
- centrioles migrate to opposite poles
Late:
- chromosomes now clearly visible as 2 chromatids joined by a centromere
- nucleolus breaks down
- spindle fibres form at the poles of the cell from the centrioles
Describe main events of metaphase:
- nuclear envelope breaks down
- spindle fibres extend across the cell
- chromosomes line up at the equator, each attached to the spindle fibres by its centromere
Describe the main events of anaphase:
- centromeres split into 2
- spindle fibres contract, pulling chromatids to opposite poles thus separating the identical DNA copies
Describe the main events of early and late telophase:
Early: - chromatids reach the poles - spindle fibres break down Late: - new nuclear membranes form - chromatids disappear - new nucleoli form
Describe cytokinesis in animal cells
Microtubules line up in centre of cell between the 2 nuclei.
They contract, constricting the cytoplasm and pulling the cell membrane inwards to form a cleavage furrow.
Cell membrane fuses with itself, splitting the cell into 2
Describe cytokinesis in animal cells
Microtubules line up in centre of cell between the 2 nuclei.
They contract, constricting the cytoplasm and pulling the cell membrane inwards to form a cleavage furrow.
Cell membrane fuses with itself, splitting the cell into 2
Describe cell division by budding in yeast
mitosis -
bud/swelling forms from the original cell called a bud - replicated organelles move into this bud and it is pinched off by cytokinesis, separating it from the parent cell. new cell is genetically identical.
Describe cell differentiation
cells become specialised in structure to carry out a particular function
What are stem cells? Where are they found in animals vs. plants?
undifferentiated cells which can divide repeatedly to form other specialised cells.
In bone marrow in humans, stem cells can form erythrocytes and neutrophils.
Meristem cells in the cambium of plants can form xylem vessels and phloem sieve tubes.
Describe how erythrocytes are specialised to perform their function
- Bioconcave disc for large surface area for uptake of O2/CO2
- no nucleus/mitochondria = more space for haemoglobin to carry O2/CO2
- lots of haemoglobin protein which combines temporarily with O2 or CO2
- small : fits through narrow blood capillaries and gets close to body cells
Describe how neutrophils are specialised to perform their function (phagocytosis)
- multilobed nucleus for engulfing
- granular cutoplasm: grains contain lysosomes containing lysin enzymes to digest bacteria
- many mitochondria for movement to ‘chase’ pathogens
Describe how epithelial cells are specialised to perform their function (lining/exchange of materials)
- squamous
- cilliated
- form a single layer of cells
- squamous consists of a single layer of flattened cells
- ciliated epithelium consists of a single layer of rectangular cells with cilia on (also some goblet cells between them which secrete mucus to trap particles which the cilia waft away
Describe how sperm cells are specialised to perform their function
- many mitochondria to produce ATP via aerobic respiration: provides energy for swimming
- acrosome: specialised lysosome with enzymes in it to break down the membrane surrounding the egg and fertilise it
- plasma membrane had receptors that bind to the egg cell membrane to allow fertilisation to occur
- nucleus contains 1 set of chromosomes - haploid - which fuses with egg nucleus to form a diploid zygote
- long undulipodium to propel itself
Describe how palisade cells are specialised to perform their function
- cylindrical shape allows many cells to fit below the upper epidermis = large surface area for light absorption
- thin cellulose walls for short diffusion/osmosis distance
- walls, cell surface membrane and cytoplasm are all transparent to allow passage of light
- vacuole pushes chloroplasts to the edges allowing maximum light absorption
- vacuole provides store of water for light dependent stage
- vacuole maintains turgor pressure to support the cell
- many chloroplasts for photosynthesis
Describe how root hair cells are specialised to perform their function
- long lateral hair-like projection gives large surface area for uptake of water
- cytoplasm contains many mitochondria to to produce ATP to provide the energy required for active transport of ions into root hair cells (lowering water potential and causing water to follow by osmosis)
- large vacuole for storage of water and ions - organelles pushed to sides
Describe how guard cells are specialised to perform their function
- in pairs surrounding each stomatal pore in the leaf epidermis
- thick cell wall on one side causes guard cells to bend when turgid, opening the stomata - collapse slightly when flaccid to close the stomata
what is a tissue?
a group of specialised cells working together to carry out a particular function
what is an organ? organ system?
a group of different tissues working together to carry ut a major function
organ system: a collection of different organs which work together
what is cell signalling?
cooperation between cells, tissues, organs and organ systems: 1 cell type produces molecules (e.g. hormones) that affect the behaviour of other cells.
Animals also use electrical impulses carried by neurones.
