Topic 2 - Cells Flashcards
Outline the cell theory
- All living organisms are composed of cells
- Cells are the smallest unit of life
- Cells only come from pre-existing cells
What are the evidence for the cell theory?
- Cell organelles cannot survive outside of the cell
- Observations of cells during division
- Spontaneous generation of life from biological organisms smaller than cells is impossible
What are the functions of life unicellular organisms carry?
- Metabolism
- Response
- Homeostasis
- Growth
- Reproduction
- Nutrition
What are the relative sizes of molecules, cell membranes, viruses, bacteria, organelles, and cells?
- molecules 1 nm
- thickness of cell membranes 10 nm
- viruses 100 nm
- bacteria 1 µm
- organelles up to 10 µm
- most cells up to 100 µm
Explain the importance of the surface area to volume ratio as a factor limiting cell size
The rate of heat/waste production and resource consumption of a cell is proportional to itse volume, whereas the rate of exchange of materials and energy (heat) is proportional to its surface area. Thus, cells with more surface area per unit volume are able to move more materials in and out of the cell.
Do multicellular organisms show emergent properties?
Yes.
How do cells differentiate to carry out specialised functions?
They express some of their genes but not others, thus making every cell specialised to its action.
How are stem cells different from regular cells?
They retain the capacity to divide and have the ability to differentiate along different pathways to any kind of cell.
Outline the therapeutic use of stem cells
- Parkinson’s and Alzheimer’s diseases by replacing dead brain cells
- Diabetes by replacing malfunctional pancreatic cells to produce insuln
- Tissue-specific stem cells that can be used to regrow different tissues around the body
Draw and label a diagram of a prokaryote
What is the function of a prokaryotic cell wall and what is it made of?
It protects and maintains the shape of the cell. It is composed of a carbohydrate-protein called peptidoglycan. Some bacteria have an additional layer of polysaccharide which makes the bacterium possible to adhere to teeth, skin, and food.
What is the function of a plasma membrane?
It controls the movement of materials in and out of the cell and plays a role in binary fission.
What is the function of cell cytoplasm?
It occupies the complete interior of the cell and cellular processes occur in it.
What is the function of pili?
They are used for attachment, for example in joining bacteria in the transfer of DNA.
What are flagella?
They allow cell motility in prokaryotes.
What are ribosomes?
Sites of protein synthesis.
What is a nucleoid?
Controls a prokaryotic cell and reproduction. (Contains naked DNA)
What is binary fission and what happens during it?
Prokaryotic cells’ way of dividing. The DNA is copied, the two daughter chromosomes attach to opposite sides, and the cell divides into two.
Draw and label a diagram of an animal cell
What is the function of free ribosomes, where are they found, and what are they composed of?
They carry out protein synthesis and are found either in the cytoplasm or attached to rough ER. They are made of RNA and protein. NB: ribosomes of eukaryotic cells are larger and denser than of prokaryotic cells.
What is endoplasmic reticulum (ER)?
An extensive network of tubules and channels that extend almost everywhere in the cell.
What is rough endoplasmic reticulum (rER)?
Usually located near the nuclear membrane. Its structure enables transportation of materials. Ribosomes are attached to the surface of rER.
What is smooth endoplasmic reticulum (sER)?
Tubules that have different enzymes on its surface. Functions include:
- production of membrane phospholipids and cellular lipids
- production of sex hormones
- detoxification of drugs (in the liver)
- storage of calcium ions
- transportation of lipid-based compounds
- aid the liver in releasing glucose
What are lysosomes and where do they come from?
Structures that lack internal structures that arise from Golgi. Fuse with old and damaged organelles within the cell to recycle nutrients. Also takes part in phagocytosis.
What is Golgi apparatus and its sides?
Carries out collection, packaging, modification, and distribution of materials synthesised in the cell. Cis side receives products from rER and trans side sends off materials in vesicles. Very important in glandular cells.
Describe mitochondria
They have their own DNA. Have a double membrane, smooth on the outer side and folded (cristae) on the inner side. Cristae provide large surface area. Inside of the organelle is filled with matrix. Produces ATP. Also produces and contains its own ribosomes.
Describe the nucleus
Basically controls the cell and without it the cell cannot reproduce. Contains DNA in the nucleolus. Produces ribosomes in the nucleolus.
Describe chloroplasts
Very similar to mitochondria. Double membrane, contains its own DNA, includes grana, thylakoids, and stroma. Granum = stack of thylakoids, thylakoid = absorbs sunlight, stroma = the fluid inside
What are vacuoles?
Storage organelles that are included in the transport of nutrients.
Compare prokaryotic and eukaryotic cells
naked DNA VS nucleus
free DNA VS enclosed DNA
no mitochondria VS yes mitochondria
70S ribosomes VS 80S ribosomes
no internal compartmentalisation VS organelles in eukaryotes
Compare plant cells and animal cells
maintained shape VS random shape
cell wall VS no cell wall
chloroplasts VS no chloroplasts
store starch VS store glycogen
Outline two roles of extracellular components
The plant cell wall maintains the cell shape, prevents excessive water intake, and holds the whole plant up against gravity.
Animal cells secrete glycoproteins that form the extracellular matrix, which functions in support, adhesion (cell-to-cell interaction), and movement.
Draw and label a diagram of the structure of a membrane
Integral proteins completely prenetrate the bilayer (control entry and removal of molecules from the cell)
Peripheral proteins attached to the surface
Cholesterol helps to regulate membrane fluidity and stability
Glycoproteins attached to peripheral proteins recognise similar cells and are involved in immune responses
How do the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes?
The properties cause the phospholipids to always align as a bilayer if there is water present. The phobic tail is repelled and therefore points inwards whereas the philic head is attracted and points outwards, forming a bilayer. The tails don’t strongly attract each other making the membrane fluid and flexible. This allows anymal cells to have a variable shape.
List the functions of membrane proteins
- Hormone binding sites
- cells have specific shapes that fit the hormone and attachment causes a change in shape - Enzymatic action
- catalyse chemical reactions - Cell adhesion
- glycoproteins hook together - Cell-to-cell communication
- glycoproteins - Channels for passive transport
- Pumps for active transport
What is diffusion?
The passive movement of particles from a region of high concentration to a region of low concentration
What is osmosis?
The passive movement of water molecules, across a partially permeable membrane, from a region of lower concentration to a region of higher concentration.
Explain passive transport across membranes by simple diffusion
Particles move from a region of high concentration to a region of low concentration
Explain passive transport across membranes by facilitated diffusion
Involves a membrane with specific carrier proteins that are capable of combining with the substance to aid its movement. The rate will level off when total saturation occurs.
Explain the steps of active transport with protein pumps (sodium-potassium)
- Protein binds to three Na ions
- Binding causes phosphorylation and ATP attaches to the protein
- Phosphorylation causes protein to change shape, thus expelling sodium ions. ADP is released and one phosphate remains
- Two K ions bind to the other site of the protein. This releases the phosphate group
- Loss of phosphate restores protein’s original shape and K ions are released to intracellular space
Explain endocytosis
Endocytosis is the intake of macromolecules. The plasma membrane pinches off to enclose macromolecules into a vesicle. The ends of the plasma membrane reattach due to hydrophobic and philic properties. Examples include phagocytosis and pinocytosis (intake of extracellular fluids).
Explain exocytosis and its steps
Essentially the reverse of endocytosis. Usually begins in the ribosomes of rER. There are four steps:
- Protein produced by ribosomes enters the lumen of rER.
- Protein exits the ER and enters the cis side of Golgi in a vesicle.
- The protein is modified in Golgi and exits on the trans side inside another vesicle.
- The vesicle fuses with the plasma membrane → secretion of the contents
Examples include pancreas cells producing insulin and neurotransmitters released at the synapses.
List the stages in the cell cycle
- Interphase (G1, S, G2)
- Mitosis
- Cytokinesis
Describe interphase
Composed of three major stages
- G1 = growth of the cell,
- S = replication of the DNA, increase in no. of mitochondria and/or chloroplasts
- G2 = cell growth and preparation for mitosis (organelles increase, DNA begins to condense, microtubules begin to form)
What are tumours the result of?
Uncontrolled cell division. Can occur in any organ or tissue.
List the stages of mitosis
(interphase)
- Prophase
- Metaphase
- Anaphase
- Telophase
Explain what happens in mitotic prophase
- Chromatin becomes more tightly coiled to form chromosomes
- Nuclear envelope disintegrates and nucleoli dissappear
- Mitotic spindle begins to form and is complete at the end of prophase
- Centromeres attach to the spindle fibres
- Centrosomes move toward opposite poles
Explain what happens in mitotic metaphase
- Chromosomes are aligned at the equator of the cell
- Centrosomes are at opposite poles
Explain what happens in mitotic anaphase
- Centromeres divide into two and the chromatids become chromosomes
- Chromosomes move toward opposite poles of the cell by shortening microtubules
- Chromosomes move centromeres first because they are the ones attached to the centrosomes
Explain what happens in mitotic telophase
- All chromosomes have arrived at the poles of the cell
- Nuclear envelopes begin to form
- Chromosomes start to form chromatin and nucleoli reappear
