cell structure Flashcards

Question

the endomembrane system consists of

Answer 1

the nuclear envelope, rough and smooth endoplasmic reticulum (ER), the Golgi apparatus as well as the cell's plasma membrane, and includes the vesicles that bud off these membranes for intracellular transport exocytosis and endocytosis.

Answer 2

small, spherical vesicles that is surrounded by a single membrane. appear as darkly staining spherical bodies under electron microscope. contain hydrolytic enzymes such as lipases, proteases and nucleases. contents of lysosomes are acidic as the enzymes have a low optimum pH of 5.

Answer 3

1. digestion of pathogens / materials ingested by phagocytosis / endocytosis 2. degradation of worn-out organelles during autophagy 3. autolysis 4. for the breakdown of extracellular content

Answer 4

after the cell carries out phagocytosis / endocytosis, the pathogen / materials are contained within a phagosome / endosome. fusion of the lysosome with the phagosme / endosome results in the formation of secondary lysosomes where ingested materials are digested.

Answer 5

(dont need exact wording just need understanding) Endocytosis is a general term for the cellular process in which substances are brought into the cell by engulfing them in a vesicle formed from the plasma membrane. Phagocytosis is a specific type of endocytosis, and the two terms are related but not interchangeable

Answer 6

worn-out organelles within a cell are fused with lysosomes, forming autophagosomes. enzymes in the lysosomes break down the organelles. the soluble products are absorbed into the surrounding cytoplasm where they may be used in the construction of new organelles.

Answer 7

upon injury or infection, hydrolytic enzymes in lysosomes are released, leading to self-destruction of the cell.

Answer 8

the sperm releases its hydrolytic enzymes by exocytosis to digest the sheath of nutrient cells surrounding the ovum, to facilitate fertilisation

Answer 9

appears under EM mostly as rod-shaped or cylindrical (but may be dumbbell or spherical) vary in size, diameter within the range 0.5-1.5μm and length about 2.5-10μm consists of a double membrane separated by an extremely narrow fluid-filled space called intermembrane space. Smooth outer membrane: Highly permeable to small solutes but blocks passage of proteins and other macromolecules Highly convoluted inner membrane which forms cristae (singular: crista): Irregular series of partitions to increase the surface area for enzyme (ATP synthase) and protein (of electron transport chain) attachment needed for cellular respiration (oxidative phosphorylation) Intermembrane space: Temporary storage of protons to generate a proton gradient for electron transport chain The membranes enclose the mitochondrial matrix which is semi-fluid and finely granular. It is the site of Krebs cycle during aerobic respiration and site of fatty acid oxidation. The matrix contains circular mitochondrial DNA (mtDNA) and 70S ribosomes, which are characteristic of prokaryotes (refer to B. Prokaryotes). These enable mitochondria to be semi-autonomous whereby they can grow and divide independently of the cel

Answer 10

site of aerobic respiration for ATP synthesis

Answer 11

by moving through the cell by cytoplasmic streaming

Answer 12

Biconvex discs / lens-shaped Enclosed by a double membrane collectively known as the chloroplast envelope The outer and inner membranes are separated by a very narrow fluid-filled intermembrane space. Outer membrane – This is a smooth, permeable membrane that allows small molecules and ions to pass freely. However, larger molecules require transport proteins. Inner membrane – This membrane is less permeable and contains specific transport proteins that regulate the movement of substances such as metabolites, ions, and proteins into and out of the chloroplast. Thylakoid membrane are found in the stroma, inside the chloroplasts. It is a system of flattened membranous sacs where the light-dependent reactions of photosynthesis occur, including the processes involving photosystems I and II, electron transport chain, and ATP synthesis. Thylakoids form stacks known as grana (singular: granum), and the thylakoid connecting the grana is known as the inter-granal thylakoid / lamellae. The fluid surrounding the thylakoid membrane is the stroma, which contains the chloroplast circular DNA, 70S ribosomes, starch grains and enzymes.

Answer 13

site of photosynthesis, where light-dependent reactions of photosynthesis occur on the thylakoid membrane and light-independent reactions occur in the stroma

Answer 14

filled with cell sap, an aqueous solution of dissolved food materials, ions, waste products and pigments. enclosed by single membrane known as tonoplast.

Answer 15

1. Stores reserves of important organic compounds (eg. protein storage in seeds) 2. Stores inorganic ions. e.g. K+ and Cl- 3. Disposal sites for metabolic by-products e.g. calcium oxalate crystals / latex, that would endanger the cell if they accumulated in the cytosol 4. May contain pigments that colour the cells. e.g red and blue pigments of petals that help attract pollinating insects to flowers, red onion. 5. May help protect the plant against predators by containing compounds that are poisonous or unpalatable to animals such as alkaloids. 6. Plays a role in plant growth by absorbing water and elongating the cell

Answer 16

usually very much smaller and less permanent than plant vacuole small vacuoles are often called vesicles and may contain engulfed solids or liquids

Answer 17

1. Food vacuoles: Formed by phagocytosis, e.g. in the case of intracellular digestion by some protozoa and macrophages 2. Contractile vacuoles: Found in many freshwater protists to pump excess water from the cell (osmoregulation) e.g. Paramecium had contractile vacuoles that pump excess water out of the cell.

Answer 18

nucleus, endoplasmic reticulum, Golgi apparatus, lysosome, mitochondria, chloroplast, vacuoles

Answer 19

ribosomes, centrioles, cytosol, cytoskeleton, cellulose cell wall

Answer 20

1. free ribosomes, which are suspended in the cytosol 2. bound ribosomes, which are attached to rough endoplasmic reticulum

Answer 21

Consists of 2 subunits – a small subunit and a large subunit. Ribosomes are composed of ribosomal proteins and rRNA. rRNA is synthesized in the nucleolus of eukaryotic cells. This is also the site where ribosomal RNA and proteins assemble into ribosomal subunits.

Answer 22

site of polypeptide synthesis during translation

Answer 23

at the free ribosomes

Answer 24

at the bound ribosomes on the rough ER

Answer 25

rRNA genes transcribed to give rRNA in the nucleolus. Ribosomal protein genes are transcribed in the nucleus to give mRNA in the nucleus. mRNA is translated at free ribosomes in the cytoplasm. Ribosomal proteins are transported into the nucleolus via nuclear pores. Ribosomal proteins and rRNA assemble in the nucleolus to form separate small and large subunits. The subunits assemble on mRNA during translation.

Answer 26

Found in animal cells and lower plant cells (e.g. algae and mosses) but absent in higher plant cells. Located next to the nucleus. Found within a region known as the centrosome during nuclear division.

Answer 27

Exist as a pair of rod-like structures, positioned with their longitudinal axis at right angles to each other Cylinder is made up of 9 triplets of microtubules arranged in a ring.

Answer 28

organise spindle fibres during cell division of animal cells

Answer 29

contains water (90%), organic molecules, inorganic ions and waste products (CO2) as well as many enzymes.

Answer 30

Store vital chemicals and site of certain metabolic pathways e.g. glycolysis, fatty acid synthesis, translation

Answer 31

microtubules, intermediate fibres, and microfilamets

Answer 32

maintain cell shape, anchor organelles, and cause cell movement

Answer 33

made of globular protein tubulin (α-tubulin and β-tubulin) tubulin tube may elongate by adding tubulin units to one end straight, hollow fibres about 25nm in diameter may occur singly or in bundles may dissociate or reassemble to build microtubules elsewhere in the cell

Answer 34

made of globular protein actin solid structures (not tubular) with diameter about 5-7nm which appears as a helix of two intertwining actin chains may occur as bundles in the cytoplasm may dissociate or reassemble to build microfilaments elsewhere in the cell

Answer 35

made of diverse proteins within the keratin family solid structure with diameter of about 10nm may occur as bundles in the cytoplasm more stable than microtubules and microfilaments to enforce cells and organise tissue

Answer 36

cellular support tracks for organelle movement (involves protein known as kinesin and dyenin) cellular movement -- formation of cilia and flagella for motility separation of chromosomes during nuclear division deposition of cellulose

Answer 37

cellular support localised contraction of cells, such as the pinching of cell into two during cell division muscle contraction cytoplasmic streaming - important in moving organelles such as mitochondria and chloroplast

Answer 38

structural role: provides mechanical strength to cells and tissues fixes the location of certain organelles e.g. nucleus sits within a cage of intermediate filaments

Answer 39

External to plasma membrane Consists of cellulose fibres embedded in an amorphous polysaccharide matrix of pectin/lignin Permeable to water and solutes

Answer 40

To provide mechanical support for plant cell and to the plant (especially herbaceous plants) As water enters the cell osmotically, the cell wall resists expansion and an internal pressure is created which provides turgidity for the cell and the plant. The strength may be increased by the presence of lignin in the matrix between the cellulose fibres.

Answer 41

peptidoglycan cell wall, plasma membrane, genetic material, 70S ribosomes

Answer 42

plasmids, capsule, flagella, pili

Answer 43

Peptidoglycan consists of parallel polysaccharide chains made of alternating units of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM), cross-linked in regular fashion by short peptide chains. Bacteria can be classified as gram positive or gram negative based on the structure of their cell walls.

Answer 44

gram positive bacteria: - Have a thick layer of peptidoglycan and no outer membrane - Stained blue-purple by gram stain gram negative bacteria: - Have a thin layer of peptidoglycan and an outer membrane / envelope. - Stained red by gram stain

Answer 45

confers the cell rigidity and shape prevents the cell from lysis when it absorbs water via osmosis

Answer 46

similar to that of the eukaryotic cells

Answer 47

mesosome (only in some bacteria) and photosynthetic membranes (only in photosynthetic bacteria)

Answer 48

infoldings of the cell membrane which are formed in some bacteria during binary fission

Answer 49

- facilitate the separation of the two daughter molecules of DNA after replication. - increase the surface area for enzymatic reactions that are associated with respiration.

Answer 50

photosynthetic pigments e.g. chlorophyll

Answer 51

Bacteria have only 1 chromosome, which is a single circular double-stranded DNA containing only several thousand genes. Found in nucleoid region (not membrane bound). Associated with histone-like proteins Transcriptionally active genes are found in loosely coiled regions Transcriptionally inactive genes found in supercoiled regions

Answer 52

Are small, self-replicating circular DNA (contains its own origin of replication) occurring in addition to the chromosomal DNA They possesses only a few genes, which generally give extra survival advantage

Answer 53

E.g. genes which confer resistance to antibiotics E.g. F plasmid contains fertility factor gene which confers sex pili

Answer 54

Is a slimy secretions of certain bacteria. Usually consist of polysaccharides.

Answer 55

Can serve to unite bacteria into colonies. Also enable bacteria to stick to surfaces such as teeth, mud and rocks, and offer useful additional protection to the bacteria.

Answer 56

rigid and wave-shaped

Answer 57

many bacteria are motile due to one or more flagella cork screw motion of flagella facilitates movement of bacteria

Answer 58

Are surface appendages / fine protein rods projecting from the walls of some bacteria. Shorter and thinner than flagella

Answer 59

aid in attachment to specific cells or surfaces

Answer 60

Sex pili are involved in bridging two bacteria, thus allowing the donor bacteria to transfer DNA to the recipient bacteria. This results in conjugation, a form of horizontal gene transfer.

Answer 61

1. viral genome 2. capsid protein 3. envelope (present only in some viruses)

Answer 62

The viral genome is a molecule of nucleic acid (either DNA or RNA) that functions as the genetic material of the virus. It can be: - single or segmented - circular or linear - single-stranded or double-stranded The genes present on the viral genome are relatively few in number, ranging from 3-1000 depending on species.

Answer 63

codes for the synthesis of the viral components and viral enzymes required for replication.

Answer 64

The capsid is the protective protein coat enclosing the viral genome. Together, the structure is known as nucleocapsid. Capsids are formed from structural subunits called capsomeres, arranged in a precise and highly repetitive pattern around the nucleic acid. The information for proper assembly of proteins into capsomeres is contained within the structure of the proteins themselves, and the overall process of assembly is thus called self-assembly.

Answer 65

The capsid serves to protect and introduce the genome into the host cells.

Answer 66

viruses without envelope

Answer 67

viruses that have complex membranous structures surrounding the polyhedral or helical nucleocapsid

Answer 68

phospholipids and glycoproteins (for most viruses)

Answer 69

they are derived from host cell membranes by a process called budding. The envelope comes from the host cell’s nuclear membrane, ER, vacuolar membranes, or cell surface membrane. Although the envelope is usually of host origin, the virus does incorporate proteins of its own, often appearing as glycoprotein spikes, into the envelope.

Answer 70

the glycoprotein spikes function in attaching the virus to receptors on susceptible host cells (recognition).

Answer 71

viruses that only infect bacteria

Answer 72

1. Genome: dsDNA 2. Capsid: Capsomeres, Sheath, Base plate, Tail fibres 3. No envelope / Naked

Answer 73

obligate intracellular parasites

Answer 74

because they must invade a cell (host) to replicate and multiply. Viruses require the host’s machinery, e.g. ribosomes and enzymes, to synthesize their own genetic materials and proteins.

Answer 75

1. Lack of Cellular Structure: Viruses are not made of cells, which are considered the basic units of life according to cell theory. 2. No Metabolism: They do not carry out metabolic processes on their own, such as energy production or nutrient assimilation. 3. Dependence on Host: Viruses cannot reproduce independently. They need a host cell to replicate, which suggests they cannot sustain life processes autonomously. 4. No Response to Stimuli: Viruses generally do not respond to environmental stimuli in the way living organisms do.

Answer 76

1. Genetic Material: Viruses contain genetic material (DNA or RNA), which they use to direct the production of new virus particles within a host cell. 2. Evolution: They can evolve over time through mutations and natural selection, a characteristic of living organisms. 3. Reproduction: While they rely on a host, they do reproduce, producing numerous copies of themselves once inside the host cell.

Answer 77

according to cell theory, viruses are not considered cells.

Answer 78

1. Living organisms are composed of one or more cells: Viruses are not made up of cells. They lack the cellular structure found in living organisms, such as a plasma membrane, cytoplasm, and organelles. 2. The cell is the basic unit of structure and function in living things: Viruses do not have the structural components or functional independence of cells. They cannot carry out metabolic processes or reproduce on their own; they require a host cell to replicate. 3. All cells arise from pre-existing cells: Viruses do not come from other cells. Instead, they replicate by assembling new virus particles inside a host cell, which is a different mechanism from cellular division (e.g., mitosis or binary fission).

cell structure Flashcards

(102 cards)