Topic 2 - Cell Theory Flashcards

Question

2.3.2What is the function of ribosomes (eukaryotic cells)?

Answer 1

Site of protein synthesis. They translate RNA to produce proteins. Found either floating free in cytoplasm or attached to rough endoplasmic reticulum.

Answer 2

A system of membranes involved in the transport of materials between organelles studded with ribosomes and involved in the synthesis and transport of proteins destined for secretion

Answer 3

Site of hydrolysis / digestion / breakdown of macromolecules

Answer 4

Site of aerobic respiration, which produces large quantities of chemical energy (ATP) from organic compounds

Answer 5

Contains hereditary material (DNA) and thus controls cell activities (via transcription) and mitosis (via DNA replication)

Answer 6

- Both have a cell membrane - Both contain ribosomes - Both have DNA and cytoplasm Prokaryotes DNA circular and found in the nucleoid (in cytoplasm). Eukaryotes DNA is linear and found in nucleus. Prokaryotes have no membrane bound organelles, eukaryotes do. Prokaryotes have 70S ribosomes, eukaryotes have 80S ribosomes. Prokaryotes reproduce asexually through binary fission, eukaryotes reproduce asexually through mitosis or sexually through meiosis. Prokaryotes DNA - haploid Eukaryotes DNA - diploid Prokaryotic cells 1-5 micrometers Eukaryotic cells 10-100 micrometers

Answer 7

Animal cells only have a plasma membrane and no cells wall,whereas plant cells have both. Plants have chloroplasts and animals cells don't. Animals store glycogen as a carbohydrate resource, plants store starch. Animal cells do not usually contain vacuoles (if present they are small and temporary) whereas plant cells have large permanent vacuoles. Animal cells can change shale due to lack of a cell wall and are usually rounded, whereas plan cells have a fixed shape, maintained by the presence of a cell wall.

Answer 8

Plant cells The cell wall in plants is made from cellulose secreted from the cell, which serves the following functions: Provides support and mechanical strength for the cell (maintains cell shape) Prevents excessive water uptake by maintaining a stable, turgid state Serves as a barrier against infection by pathogens Animal cells The extracellular matrix (ECM) is made from glycoproteins secreted from the cell, which serve the following functions: Provides support and anchorage for cells Segregates tissues from one another Regulates intercellular communication by sequestering growth factors

Answer 9

Consist of a polar head (hydrophilic) made from glycerol and phosphate Consist of two non-polar fatty acid tails (hydrophobic) Arrangement in Membrane Phospholipids spontaneously arrange in a bilayer Hydrophobic tail regions face inwards and are shielded from the surrounding polar fluid while the two hydrophilic head regions associate with the cytosolic and extracellular environments respectively Structural Properties of Phospholipid Bilayer Phospholipids are held together in a bilayer by hydrophobic interactions (weak associations) Hydrophilic / hydrophobic layers restrict entry and exit of substances Phospholipids allow for membrane fluidity / flexibility (important for functionality) Phospholipids with short or unsaturated fatty acids are more fluid Phospholipids can move horizontally or occasionally laterally to increase fluidity Fluidity allows for the breaking / remaking of membranes (exocytosis / endocytosis)

Answer 10

Membrane proteins can act as hormone binding sites, electron carriers, pumps for active transport, channels for passive transport and also enzymes. In addition they can be used for cell to cell communication as well as cell adhesion.

Answer 11

The net movement of particles from a region of high concentration to a region of low concentration (along the gradient) until equilibrium

Answer 12

The net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration until equilibrium is reached

Answer 13

The plasma membrane is semi-permeable and selective in what can cross Substances that move along the concentration gradient (high to low) undergo passive transport and do not require the expenditure of energy (ATP) Small, non-polar (lipophilic) molecules can freely diffuse across the membrane

Answer 14

The plasma membrane is semi-permeable and selective in what can cross Substances that move along the concentration gradient (high to low) undergo passive transport and do not require the expenditure of energy (ATP) Larger, polar substances (ions, macromolecules) cannot freely diffuse and require the assistance of transport proteins (carrier proteins and channel proteins) to facilitate their movement (facilitated diffusion)

Answer 15

Active transport is the passage of materials against a concentration gradient (from low to high) This process requires the use of protein pumps which use the energy from ATP to translocate the molecules against the gradient The hydrolysis of ATP causes a conformational change in the protein pump resulting in the forced movement of the substance Protein pumps are specific for a given molecule, allowing for movement to be regulated (e.g. to maintain chemical or electrical gradients) An example of an active transport mechanism is the Na+/K+ pump which is involved in the generation of nerve impulses

Answer 16

Polypeptides destined for secretion contain an initial target sequence (a signal recognition peptide) which directs the ribosome to the endoplasmic reticulum The polypeptide continues to be synthesised by the ribosome into the lumen of the ER, where the signal sequence is removed from the nascent chain The polypeptide within the rough ER is transferred to the golgi apparatus via a vesicle, which forms from the budding of the membrane The polypeptide moves via vesicles from the cis face of the golgi to the trans face and may be modified along the way (e.g. glycosylated, truncated, etc.) The polypeptide is finally transferred via a vesicle to the plasma membrane, whereby it is either immediately released (constitutive secretion) or stored for a delayed release in response to some cellular signal (regulatory secretion = for a more concentrated and more sustained effect)

Answer 17

The membrane is principally held together by the relatively weak hydrophobic associations between phospholipids This association allows for membrane fluidity and flexibility, as the phospholipids (and to a lesser extent the proteins) can move about to some extent This allows for the breaking and remaking of membranes, allowing larger substances access into and out of the cell (this is an active process) Endocytosis The process by which large substances (or bulk amounts of smaller substances) enter the cell without travelling across the plasma membrane An invagination of the membrane forms a flask-like depression which envelopes the material; the invagination is then sealed off forming a vesicle There are two main types of endocytosis: 1. Phagocytosis The process by which solid substances (e.g. food particles, foreign pathogens) are ingested (usually to be transported to the lysosome for break down) 2. Pinocytosis The process by which liquids / solutions (e.g. dissolved substances) are ingested by the cell (allows quick entry for large amounts of substance)

Answer 18

The process by which large substances exit the cell without travelling across the plasma membrane Vesicles (usually derived from the golgi) fuse with the plasma membrane expelling their contents into the extracellular environment

Answer 19

The cell cycle is an ordered set of events that culminates in cell growth and division into two daughter cells It can roughly be divided into two main stages: Interphase The stage in the development of the cell between two successive M phases This phase of the cell cycle is a continuum of 3 distinct stages (G1, S, G2), whereby the cell grows and matures (G1), copies its DNA (S) and prepares for division (G2) Sometimes cells will leave the cell cycle and enter into a quiescent state (G0), whereby it becomes amitotic and no longer divides M phase The periods of nuclear division (mitosis) and cytoplasmic division (cytokinesis)

Answer 20

The cell cycle is controlled by a complex chemical control system that responds to signals both inside and outside of the cell Tumor suppressor genes produce proteins which inhibit cell division, while proto-oncogenes produce proteins that promote growth and division Mutations to these genes result in uncontrolled cell division, resulting in the formation of a tumour Tumours can grow in size which causes damage local tissue; they may also spread to other parts of the body (malignant tumours) Diseases caused by the growth of tumours are collectively known as cancers

Answer 21

Interphase is an active period in the life of a cell - many events need to occur before a cell can successfully undergo division: Protein synthesis: The cell needs to synthesise key proteins and enzymes to enable it to grow, copy its contents and then divide ATP production: The cell will need to generate sufficient quantities of ATP in order to successfully divide Increase number of organelles: The cell needs to ensure both daughter cells will have the necessary numbers of organelles needed to survive DNA replication: The genetic material must be faithfully duplicated before division (this occurs during the S phase) As none of these processes can occur during the M phase, interphase contains growth checkpoints to ensure division is viable G1: A checkpoint stage before DNA replication during which the cell grows, duplicates organelles, synthesises proteins and produces ATP S: The stage during which DNA is replicated G2: A checkpoint stage before division during which the copied DNA is checked for fidelity (mutations) and final metabolic reactions occur

Answer 22

Prophase DNA supercoils, causing chromosomes to condense and become visible under a light microscope As DNA was replicated during interphase, the chromosomes are each comprised of two genetically identical sister chromatids joined at a centromere The centrosomes move to opposite poles of the cell and spindle fibres begin to form between them (in animals, each centrosome contains 2 centrioles) The nuclear membrane is broken down and disappears Metaphase Spindle fibres from the two centrosomes attach to the centromere of each chromosome Contraction of the microtubule spindle fibres cause the chromosomes to line up separately along the centre of the cell (equatorial plane) Anaphase Continued contraction of the spindle fibres cause the two sister chromatids to separate and move to the opposite poles of the cell Once the two chromatids in a single chromosome separate, each constitutes a chromosome in its own right Telophase Once the two sets of identical chromosomes arrive at the poles, the spindle fibres dissolve and a new nuclear membrane reforms around each set of chromosomes The chromosomes decondense and are no longer visible under a light microscope The division of the cell into two daughter cells (cytokinesis) occurs concurrently with telophase

Answer 23

During interphase (the S phase) the DNA was replicated to produce two copies of genetic material These two identical DNA molecules are identified as sister chromatids and are held together by a single centromere During the events of mitosis (as described in 2.5.4), the sister chromatids are separated and drawn to opposite poles of the cell When the cell divides (cytokinesis), the two resulting nuclei will each contain one of each chromatid pair and thus be genetically identical

Answer 24

Growth: Multicellular organisms increase their size by increasing their number of cells through mitosis Asexual reproduction: Certain eukaryotic organisms may reproduce asexually by mitosis (e.g. vegetative reproduction) Tissue Repair: Damaged tissue can recover by replacing dead or damaged cells Embryonic development: A fertilised egg (zygote) will undergo mitosis and differentiation in order to develop into an embryo