Topic 1 Cell Biology Flashcards

Question

Outline the difference between eukaryotic and prokaryotic cells. ## Footnote 1.2

Answer 1

* Cytoplasm is divided into compartments by single or double membranes to form organelles in eukaryotic cells * eukaryotes have a nucleus whereas prokaryotes do not ## Footnote Understanding: Eukaryotes have a compartmentalized cell structure.

Answer 2

* **Structure**: Double membrane structure with pores; contains an inner region called a nucleolus * **Function**: Stores genetic material (DNA) as chromatin, where DNA is replicated and transcribed to form mRNA ## Footnote Draw the ultrastructure of eukaryotic cells based on electron micrographs.

Answer 3

* **Structure**: consists of flattened membrane sacs, called cisternae. Attached to the outside of these cisternae are ribosomes * **Function**: synthesize protein for secretion from the cell ## Footnote Draw the ultrastructure of eukaryotic cells based on electron micrographs.

Answer 4

* **Structure**: An assembly of vesicles and folded membranes located near the cell membrane * **Function**: processes proteins brought in vesicles from the rER ## Footnote Draw the ultrastructure of eukaryotic cells based on electron micrographs.

Answer 5

* **Structure**: spherical with a single membrane. They are formed from Golgi vesicles. They contain high concentrations of protein, which makes them densely staining in electron micrographs. * **Function**: contain digestive enzymes, used to break down ingested food in vesicles or break down organelles in the cell ## Footnote Draw the ultrastructure of eukaryotic cells based on electron micrographs.

Answer 6

* **Structure**: double membraned, inner membrane forms cristae. * **Function**: They produce ATP for the cell by aerobic cell respiration. ## Footnote Draw the ultrastructure of eukaryotic cells based on electron micrographs.

Answer 7

* **Structure**: appear as dark granules in the cytoplasm (80S) * **Function**: synthesize protein ## Footnote Draw the ultrastructure of eukaryotic cells based on electron micrographs.

Answer 8

* **Structure**: double membraned, stacks of thylakoids, which are fattened sacs of membrane. * **Function**: produce glucose, Starch grains may be present inside chloroplasts if they have been photosynthesizing rapidly. ## Footnote Draw the ultrastructure of eukaryotic cells based on electron micrographs.

Answer 9

* **Structure**: single membrane with fluid inside * **Function**: **vacuoles** (absorb foods from outside and digest them inside vacuoles), **vesicles** (small vacuoles used to transport materials inside the cell) ## Footnote Draw the ultrastructure of eukaryotic cells based on electron micrographs.

Answer 10

microtubules * **Structure**: small cylindrical fibres * **Function**: moving chromosomes during cell division centrioles * **Structure**: two groups of nine triple microtubules * **Function**: form an anchor point for microtubules during cell division ## Footnote Draw the ultrastructure of eukaryotic cells based on electron micrographs.

Answer 11

* **Structure**: whip-like structures projecting from the cell surface, flagella (one and larger), cilia (many and smaller) * **Function**: used for locomotion ## Footnote Draw the ultrastructure of eukaryotic cells based on electron micrographs.

Answer 12

Exocrine gland cells in the pancreas secrete digestive enzymes into a duct that carries them to the small intestine where they digest foods. * a lot of ribosomes, mitochondria, and rER * needed to created proteins (enzymes) for its function * plasma membrane, mitochondrion, nucleus, rough ER, golgi apparatus, vesicles, lysosomes ## Footnote Application: The structure and function of organelles within exocrine gland cells of the pancreas.

Answer 13

The cell type that carries out most photosynthesis in the leaf is palisade mesophyll. * **chloroplast**, cell wall, plasma membrane, mitochondrion, vacuole, nucleus * photsynthesizes thus needs chloroplast ## Footnote Application: The structure and function of organelles within palisade mesophyll cells ofthe leaf.

Answer 14

* Consist of a polar head (hydrophilic) composed of a glycerol and a phosphate molecule * Consist of two non-polar tails (hydrophobic) composed of fatty acid (hydrocarbon) chains * Because phospholipids contain both hydrophilic (water-loving) and lipophilic (fat-loving) regions, they are classed as **amphipathic** ## Footnote Understanding: Phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules.

Answer 15

* When phospholipids are mixed with water the phosphate heads are attracted to the water but the hydrocarbon tails are attracted to each other, but not to water. * Become arranged into double layers: * **Hydrophobic hydrocarbon tails facing inwards** towards each other and the **hydrophilic heads facing the water on either side** ## Footnote Understanding: Phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules.

Answer 16

This model showed a bilayer of phospholipids in the center with proteins on both sides. 1. Calculated that there were twice as many phospholipids than would be needed for monolayer (must be a bilayer) 2. electron micrographs showed “railroad track” appearance (Proteins appear dark and phospholipids appear light) ## Footnote Skill: Analysis of evidence from electron microscopy that led to the proposal of the Davson-Danielli model.

Answer 17

**Assumptions:** * All membranes were the same thickness and would have a constant lipid-protein ratio * All membranes would have symmetrical internal and external surfaces ## Footnote Skill: Analysis of the falsification of the Davson-Danielli model that led to the Singer-Nicolson model

Answer 18

1.Freeze-etched electron micrographs * Fracture reveals an irregular rough surface inside the phospholipid bilayer * Refutes the point that they are only found on the outside of the membrane 2.Structure of membrane proteins * Proteins extracted found to be different in size and shape * Refutes uniform/continuous layer hypothesis * Proteins found to all have hydrophobic section )would embed in “tails”) * Refutes proteins found only on outer layer 3.Fluorescent antibody tagging * The membrane proteins of some cells were tagged with red markers and other cells with green markers. * The cells were fused together. Within 40 minutes the red and green markers were mixed throughout the membrane of the fused cell. * Membrane proteins are free to move within the membrane rather than being fixed in a peripheral layer. ## Footnote Skill: Analysis of the falsification of the Davson-Danielli model that led to the Singer-Nicolson model

Answer 19

1. Hormone binding sites 2. Immobilized enzymes with the active site on the outside 3. Cell adhesion to form tight junctions between groups of cells in tissues and organs. 4. Cell-to-cell communication (receptors for neurotransmitters) 5. Channels for passive transport to allow hydrophilic particles across by facilitated difusion. 6. Pumps for active transport which use ATP to move particles across the membrane. ## Footnote Understanding: Membrane proteins are diverse in terms of structure, position in the membrane and function.

Answer 20

Integral proteins * hydrophobic on at least part of their surface * embedded in the membrane * can be transmembrane Peripheral proteins * hydrophilic * not embedded in the membrane * Most of them are attached to the surface of integral proteins * Some have a single hydrocarbon chain attached to them which is inserted into the membrane, anchoring the protein to the membrane surface. Glycoproteins * have sugar units attatched to the outer surface of the membrane ## Footnote Understanding: Membrane proteins are diverse in terms of structure, position in the membrane and function.

Answer 21

* Myelin sheath around nerve cells insulate (18% protein content) * Most plasma membranes (50%) * Mitochondria (cell respiration) and chloroplasts (photosynthesis) -->75% ## Footnote Understanding: Membrane proteins are diverse in terms of structure, position in the membrane and function.

Answer 22

* Cholesterol is an amphipathic molecule (like phospholipids), meaning it has both hydrophilic and hydrophobic regions * Cholesterol’s hydroxyl (-OH) group is hydrophilic and aligns towards the phosphate heads of phospholipids * The remainder of the molecule (steroid ring and hydrocarbon tail) is hydrophobic and associates with the phospholipid tails ## Footnote Understanding: Cholesterol is a component of animal cell membranes.

Answer 23

* Fluid enough that the cell can move * Fluid enough that the required substances can move across the membrane * If too fluid however the membrane could not effectively restrict the movement of substances across itself ## Footnote Application: Cholesterol in mammalian membranes reduces membrane fuidity and permeability to some solutes.

Answer 24

* **Reduces membrane fluidity by restricting motion of phospholipids molecules** * **Disrupts tight packing of hydrophobic tails in the bilayer**, increase flexibility by **preventing the tails from crystallising** and hence behaving like a solid. * Reduces permeability to some solutes (hydrophilic) * Helps membranes curve into a concave shape (formation of vesicles during endocytosis) ## Footnote Application: Cholesterol in mammalian membranes reduces membrane fuidity and permeability to some solutes.

Answer 25

The membrane is principally held together by weak hydrophobic associations between the fatty acid tails of phospholipids This weak association allows for membrane fluidity and flexibility, as the phospholipids can move around to some extent ## Footnote Understanding: The fuidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis.

Answer 26

1. Part of the plasma membrane is pulled inwards 2. A droplet of fluid becomes enclosed when a vesicle is pinched off 3. Vesicles can then move through the cytoplasm carrying their contents ## Footnote Understanding: Vesicles move materials within cells.

Answer 27

1. Proteins are synthesized by ribosomes and then enter the rough endoplasmic reticulum 2. Vesicles bud off from the rER and carry the proteins to the Golgi apparatus 3. The golgo apparatus modifies the proteins 4. Vesicles bud off from the Golgi apparatus and carry the modified proteins to the plasma membrane 5. Vesicles fuse with the plasma membrane 6. The contents of the vesicle are expelled 7. The membrane then flattens out again ## Footnote Understanding: Vesicles move materials within cells.

Answer 28

1. Part of the plasma membrane is pulled inwards 2. A droplet of fluid becomes enclosed when a vesicle is pinched off 3. Vesicles can then move through the cytoplasm carrying their contents ## Footnote Understanding: Vesicles move materials within cells.

Answer 29

Diffusion is the net movement of molecules from a region of high concentration to a region of low concentration * This directional movement along a gradient is passive and will continue until molecules become evenly dispersed (equilibrium) * Small and non-polar (lipophilic) molecules will be able to freely diffuse across cell membranes (e.g. O2, CO2, glycerol) ## Footnote Understanding: Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.

Answer 30

* Temperature (affects kinetic energy of particles in solution) * Molecular size (larger particles are subjected to greater resistance within a fluid medium) * Steepness of gradient (rate of diffusion will be greater with a higher concentration gradient) ## Footnote Understanding: Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.

Answer 31

Facilitated diffusion is the passive movement of molecules across the cell membrane via the aid of a membrane protein * from an area of high concentration to an area of low concentration through a selectively permeable membrane with the help of **protein channels**. ## Footnote Understanding: Particles move across membranes by simple difusion, facilitated difusion, osmosis and active transport.

Answer 32

The passive net movement of water molecules from an area of low [SOLUTE] to high [SOLUTE] through a selectively permeable membrane. ## Footnote Understanding: Particles move across membranes by simple difusion, facilitated difusion, osmosis and active transport.

Answer 33

* Solutions with a relatively higher osmolarity are categorised as hypertonic (high solute concentration ⇒ gains water) * Solutions with a relatively lower osmolarity are categorised as hypotonic (low solute concentration ⇒ loses water) * Solutions that have the same osmolarity are categorised as isotonic (same solute concentration ⇒ no net water flow) ## Footnote Skill: Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions.

Answer 34

Tissue osmolarity may be inferred by identifying the concentration of solution at which there is no weight change (i.e. isotonic) ## Footnote Skill: Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions.

Answer 35

* Active transport uses energy to move molecules **against a concentration gradient** * This energy may either be generated by the **hydrolysis of ATP** * **Active transport involves the use of carrier proteins (called protein pumps due to their use of energy)** 1. A specific solute will bind to the protein pump on one side of the membrane 2. The hydrolysis of ATP (to ADP + Pi) causes a conformational change in the protein pump 3. The solute molecule is consequently translocated across the membrane (against the gradient) and released ## Footnote Understanding: Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport

Answer 36

1. Three sodium ions bind to intracellular sites on the sodium-potassium pump 2. A phosphate group is transferred to the pump via the hydrolysis of ATP 3. The pump undergoes a conformational change, translocating sodium across the membrane 4. The conformational change exposes two potassium binding sites on the extracellular surface of the pump 5. The phosphate group is released which causes the pump to return to its original conformation 6. This translocates the potassium across the membrane, completing the ion exchange ## Footnote Application: Structure and function of sodium-potassium pumps for active transport.

Answer 37

1. At one stage during a nerve impulse there are relatively more positive charges inside. 2. This voltage change causes potassium channels to open, allowing potassium ions to diffuse out of the axon. 3. Once the voltage conditions change the channel rapidly closes again. ## Footnote Application: Structure and function of sodium-potassium pumps for active transport and potassium channels for facilitated difusion in axons.

Answer 38

Uncontrolled osmosis will have negative effects with regards to cell viability: * In hypertonic solutions, water will leave the cell causing it to shrivel (crenation) * In hypotonic solutions, water will enter the cell causing it to swell and potentially burst (lysis) ## Footnote Application: Tissues or organs to be used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis.

Answer 39

If we accept that humans evolved from pre-existing ancestral species, we can trace the origins of cells back through hundreds of millions of years to the earliest cells on Earth. ## Footnote Understanding: Cells can only be formed by division of pre-existing cells.

Answer 40

1. Broths were stored in vessels that contained long tubings (swan neck ducts) that did not allow external dust particles to pass 2. The broths were boiled to kill any micro-organisms present in the growth medium (sterilisation) 3. Growth only occurred in the broth if the flask was broken open, exposing the contents to contaminants from the outside **From this it was concluded that emergent bacterial growth came from external contaminants and did not spontaneously occur** ## Footnote Application: Evidence from Pasteur's experiments that spontaneous generation of cells and organisms does not now occur on Earth.

Answer 41

1. Non-living synthesis of simple organic molecules (Miller and Urey experiment showed that early earth conditions could form organic molecules) 2. Assembly of these organic molecules into polymers (deep sea vents have the right condition to form organic polymers) 3. Formation of membranes to package the organic molecules (if there were phospholipid like coumpounds, they could form an internal environment similar to the cell) 4. Formation of polymers that can self-replicate (RNA may have been the genetic material before DNA) ## Footnote Understanding: The frst cells must have arisen from non-living material.

Answer 42

**Mitochondria:** * Cell that respired anaeoribcally took in a bacterium that respired aerobically * bacterium supplied itself and the larger cell with ATP * Larger cell gets an advantage of respiring aerobically * Symbiotic relationship: The smaller cell gets supplied with food, larger cell gets energy from aerobic respirationfrom smaller cell. * Aerobic bacterium evolved into the mirochondria and larger cell evolved into heterotrophic eukaryotes **Chloroplast:** * Heterotrophic cell took in smaller photosynthetic bacterium * photosynthetic prokaryote eveolved into chloroplast and larger cell evolved into photosynthetic eukaryotics ## Footnote Understanding: The origin of eukaryotic cells can be explained by the endosymbiotic theory.

Answer 43

* They have their own genes, on a circular DNA molecule like that of prokaryotes. * They have their own 70S ribosomes of a size and shape typical of some prokaryotes. * They transcribe their DNA and use the mRNA to synthesize some of their own proteins. * They can only be produced by division of pre-existing mitochondria and chloroplasts. ## Footnote Understanding: Understanding: The origin of eukaryotic cells can be explained by the endosymbiotic theory.

Answer 44

The cell cycle is an ordered set of events which culminates in the division of a cell into two daughter cells. ## Footnote Understanding: Mitosis is division of the nucleus into two genetically identical daughter nuclei.

Answer 45

Mitosis is involved whenever cells with genetically identical nuclei are required in eukaryotes: during **embryonic development, growth, tissue repair and asexual reproduction.** ## Footnote Understanding: Mitosis is division of the nucleus into two genetically identical daughter nuclei.

Answer 46

Interphase - part of the cell cycle that does not involve division; majority of life cycle **G1 (Gap 1):** * Metabolic reactions * Increase volume of cytoplasm * Organelles produced and replicated * Proteins synthesised **S (Synthesis)** * DNA replicated **G2 (Gap 2)** * Metabolic reactions * Increase the volume of the cytoplasm * Organelles produced and replicated * Proteins synthesised **G0 (Gap 0)** * “Resting phase” * Temporary or permanent phase * Cells that do not divide * Carry out regular functions * Metabolic reactions ## Footnote Understanding: Interphase is a very active phase of the cell cycle with many processes occurring in the nucleus and cytoplasm.

Answer 47

Condensation occurs by means repeatedly coiling the DNA molecule to make the chromosome shorter and wider. This process is called **supercoiling.** ## Footnote Understanding: Chromosomes condense by supercoiling during mitosis.

Answer 48

the part of a chromosome that links sister chromatids ## Footnote Understanding: Chromosomes condense by supercoiling during mitosis.

Answer 49

Sister chromatids are duplicated chromosomes attached by a centromere After anaphase when the sister chromatids separate they should then be referred to as daughter chromosomes ## Footnote Understanding: Chromosomes condense by supercoiling during mitosis.

Answer 50

centrioles organise spindle microtubules ## Footnote Understanding: Chromosomes condense by supercoiling during mitosis.

Answer 51

Spindle microtubules (also referred to as spindle fibres) ## Footnote Understanding: Chromosomes condense by supercoiling during mitosis.

Answer 52

**Chromatin:** * loosely packed DNA within the nucleus as unravelled chromatin * DNA is organised as chromatin in interphase **Chromosome:** * DNA is condensed prior to division (via supercoiling) * DNA is able to be easily seperated and moved * During the process of mitosis (condense in prophase, decondense in telophase) ## Footnote Understanding: Chromosomes condense by supercoiling during mitosis.

Answer 53

* **DNA supercoils** and chromosomes condense (becoming visible under microscope) * Chromosomes are comprised of genetically identical **sister chromatids** (joined at a centromere) * Paired **centrosomes move to the opposite poles of the cell** and form microtubule spindle fibres * The **nuclear membrane breaks down and the nucleus dissolves** ## Footnote Skills: Identifcation of phases of mitosis in cells viewed with a microscope.

Answer 54

* **Microtubule spindle fibres** from both centrosomes **connect to the centromere** of each chromosome * **Chromosomes to align along the centre of the cell** (equatorial plane or metaphase plate) ## Footnote Skills: Identifcation of phases of mitosis in cells viewed with a microscope.

Answer 55

* Contraction of the spindle fibres causes genetically identical **sister chromatids to separate** * Sister chromatids seperate to become chromosomes * The genetically identical chromosomes **move to the opposite poles of the cell** ## Footnote Skills: Identifcation of phases of mitosis in cells viewed with a microscope.

Answer 56

* Once the **two chromosome sets arrive at the poles**, spindle fibres dissolve * **Chromosomes decondense** (no longer visible under light microscope) * **Nuclear membranes reform** around each chromosome set * **Cytokinesis occurs** concurrently, splitting the cell into two ## Footnote Skills: Identifcation of phases of mitosis in cells viewed with a microscope.

Answer 57

mitotic index= # of cells in mitosis/ total # of cells ## Footnote Skill: Determination of a mitotic index from a micrograph.

Answer 58

**Animal cells:** * Plasma membrane is pulled inwards around the equator * Forms a cleavage furrow (using proteins) * When the cleavage furrow reaches the centre, the cell is pinched apart into two daughter cells. **Plant cells: ** * Vesicles form in a row at the centre of the cell (equatorial plane) * The vesicles fuse together and an early cell plate begins to form within the middle of the cell * The cell plate extends outwards and fuses with the cell wall, dividing the cell into two distinct daughter cells ## Footnote Understanding: Cytokinesis occurs after mitosis and is diferent in plant and animal cells.

Answer 59

Cyclins are a group of proteins that control the progression of the cell cycle. 1. Cells cannot progress to the next stage of the cell cycle unless the specific cyclin reaches it threshold. 2. Cyclins bind to enzymes called cyclin-dependent kinases 3. These kinases then become active and attach phosphate groups to other proteins in the cell. 4. The attachment of phosphate triggers the other proteins to become active and carry out tasks (specific to one of the phases of the cell cycle). ## Footnote Understanding: Cyclins are involved in the control of the cell cycle.

Answer 60

* **Cyclin D:** Triggers cells to move from G0 to G1 and from G1 into S phase. * **Cyclin E:** prepares the cell for DNA replication in S phase. * **Cyclin A:** activates DNA replication inside the nucleus in S phase. * **Cyclin B**: promotes the assembly of the mitotic spindle and other tasks in the cytoplasm to prepare for mitosis. ## Footnote Understanding: Cyclins are involved in the control of the cell cycle.

Answer 61

An oncogene is a gene that has the potential to cause cancer * In a normal cell oncogenes are involved in the control o the cell cycle and cell division. * This is why **mutations in oncogenes can result in uncontrolled cell division and therefore tumour formation.** ## Footnote Understanding: Mutagens, oncogenes and metastasis are involved in the development of primary and secondary tumours.

Answer 62

Tumours are **abnormal cell growths resulting from uncontrolled cell division** and can occur in any tissue or organ * Diseases caused by the growth of tumours are collectively known as cancers ## Footnote Understanding: Mutagens, oncogenes and metastasis are involved in the development of primary and secondary tumours.

Answer 63

* Tumour cells may either remain in their original location (benign) or spread and invade neighbouring tissue (malignant) * **Metastasis is the spread of cancer from one location (primary tumour) to another, forming a secondary tumour** ## Footnote Understanding: Mutagens, oncogenes and metastasis are involved in the development of primary and secondary tumours.

Answer 64

**Several mutations must occur in the same cell** for it to become a tumour causing cell. The **probability of this happening in a single cell is extremely small.** Factors (other than exposure to mutagens) that** increase the probability of tumour** development include: * The **vast number of cells in a human body – the greater the number of cells the greater the chance of a mutation.** * The **longer a life span** the greater the chance of a mutation. ## Footnote Understanding: Mutagens, oncogenes and metastasis are involved in the development of primary and secondary tumours.

Answer 65

* Cigarette smoke contains chemical compounds known to be carcinogenic * There appears to be a **strong positive correlation between the frequency of smoking and the development of cancer** * The **risk of lung cancer** is strongly correlated with smoking, with ~90% of lung cancers attributable to tobacco use * Smoking also increases the risk of over a dozen other cancers, including mouth, stomach, liver, panceas and bowel ## Footnote Application: The correlation between smoking and incidence of cancers.