Anatomy of the Cell

Question 1

Composition of a Cell

Answer 1

water - 80%; protein - 15%; lipid 0 2.5%; carbohydrate - 1.5%; inorganic (sodium/phosphate etc.) - 1%

Question 2

Eukaryotic Cell

Answer 2

a cell with a true nucleus

Question 3

Common Features of Eukaryotic cells

Answer 3

outer membrane; inner cytosol; cytoskeleton; membrane bound organelles; inclusions.

Question 4

Plasmalemma (Cell Membrane)

Answer 4

separates the cytoplasm from the outside environment. Is a layer of amphipathic phospholipid molecules with hydrophilic heads at the outer and inner surfaces and hydrophobic fatty acid chains facing towards the middle of the 2 layers. Contains integral proteins which the cell inserts into the membrane and gives the cell its ability to exocytose and endocytose material through the cell membrane.

Question 5

Integral Proteins include

Answer 5

receptors; channels; transporters; enzymes; and cell attachment proteins.

Question 6

Exocytose

Answer 6

move material (molecules) out of the cell.

Question 7

Endocytose

Answer 7

substances are brought into the cell.

Question 8

Properties of Plasmalemma

Answer 8

Is fluid, changes shape easily; is selectively permeable, highly permeable to water, oxygen, small hydrophobic molecules, virtually impermeable to charged ions (eg. Na+).

Question 9

Organelles

Answer 9

Small, intracellular ‘organs’ with a specific function and structural organisation.

Question 10

Mitochondria (organelle)

Answer 10

energy production

Question 11

Rough Endoplasmic Reticulum (organelle)

Answer 11

protein synthesis

Question 12

Smooth Endoplasmic Reticulum (organelle)

Answer 12

cholesterol and lipid synthesis/detoxification

Question 13

Golgi Apparatus (organelle)

Answer 13

modification and packaging of secretions

Question 14

Lysosomes (organelle)

Answer 14

hydrolytic enzymes for intracellular digestion

Question 15

Nucleus (organelle)

Answer 15

contains genetic code

Question 16

Inclusions

Answer 16

dispensable and may only be present for a short time. Represent components that have been synthesised by the cell itself (pigment, glycogen stores, lipid droplets, presecretion product) or taken up from the extracellular environment (endocytotic vesicle).

Question 17

Cytoskeleton

Answer 17

function maintained by a set of filamentous cytosolic proteins, the cytoskeletal proteins. Three main types: Microfilaments composed of the protein actin; Intermediate filaments composed of six main proteins, which vary in different cell types; Microtubules composed of two tubulin proteins. These filamentous proteins attach to cell membrane and to each other by anchoring and joining proteins to form a dynamic 3D internal scaffolding.

Question 18

Microfilaments

Answer 18

Composed of fine strands of the protein actin. Actin molecules can assemble into filaments and later dissociate making them very dynamic

Question 19

Intermediate Filaments

Answer 19

bind intracellular elements together and to the plasmalemma. Different types divided into classes. Provide majority of structural integrity of cell.

Question 20

Microtubules

Answer 20

hollow tubules composed of alpha and beta tubulin subunits in alternating array. Can be assembled and disassembled. Originate from centrosome and include stabilising proteins, microtubule-associated proteins (MAPS). Are polar. Important in cilia, flagella and mitotic spindle - cell movement.

Question 21

Centrosome

Answer 21

microtubules radiate from this. Core of the centrosome contains a pair of centrioles which are composed of specialised microtubule segments.

Question 22

Red Blood Cell

Answer 22

7 microns in diameter

Question 23

Nucleus contains

Answer 23

chromosomes and is location of RNA synthesis. Both mRNA and tRNA are transcribed in the nucleus, and rRNA is transcribed in the nucleolus (a 1-3micrimetre diameter dense area within the nucleus).

Question 24

Nucleus is enclosed by

Answer 24

a nuclear envelope, a double membrane with small fluid filled space (perinuclear membrane) between inner and outer membrane.

Question 25

Euchromatin

Answer 25

DNA that is partially unwound, more dispersed, and actively undergoing transcription.

Question 26

Heterochromatin

Answer 26

DNA is highly condensed (clumped) and not undergoing transcription.

Question 27

Ribosomes

Answer 27

formed in the nucleus, required for protein synthesis. Each ribosome is made up of a small subunit - which binds RNA, and a large subunit - which catalyses the formation of peptide bonds.

Question 28

Endoplasmic Reticulum

Answer 28

Forms a network of interconnecting membrane-bound compartments in the cell. Two types; rough and smooth.

Question 29

Rough Endoplasmic Reticulum

Answer 29

Studded with ribosomes. Vital role in synthesis of proteins destined for insertion into membranes or for secretion. Cells relatively metabolically inactive have relatively little ER. Associated with protein synthesis and initiation of glycoprotein formation.

Question 30

Smooth Endoplasmic Reticulum

Answer 30

continues processing of proteins produced in the RER. SER plays vital role as site of synthesis of lipids. Most cells contain relatively little SER

Question 31

Golgi Apparatus (Complex)

Answer 31

composed of a group of flattened, membrane bound cisternae, arranged in sub compartments. Transport vesicles arrive from the SER/RER. Golgi cisterns function in the modification and packaging of macromolecules that were synthesised in ER (adds sugars, cleaves some proteins, sorts macromolecules into vesicles).

Question 32

Mitochondria

Answer 32

Composed of an outer and inner membrane. Inner membrane is folded to form cristae, which increase available surface area. Function in the generation of ATP, via oxidative phosphorylation, and in the synthesis of certain lipids and proteins. Contain their own DNA and system for protein production.

Question 33

Intracellular Junctions

Answer 33

specialised membrane structures which link cells together into a functional unit. Three types of junction: Occluding junction - link cells to form a diffusion barrier; Anchoring barrier - provide mechanical strength; Communicating junction - allow movement of molecules between cells.

Question 34

Occluding Junctions (also known as tight junctions or zonula occludens)

Answer 34

Prevent diffusion. Appear as a focal region of close apposition between adjacent cell membranes

Question 35

Anchoring Junction (also termed zonula adherens)

Answer 35

Two types: Adherent - attached to actin. Attaches skeleton of one cell to skeleton of another; Desmosome - very strong. Attached to intermediate filaments. Cells in epidermis are held together by thousands of desmosomes in every cell. Make skin strong.

Question 36

Junctional Complex

Answer 36

Close association of several types of junctions found in certain epithelial tissues.

Question 37

Communicating Junctions (often termed Gap Junctions)

Answer 37

Allow selective diffusion of molecules between adjacent cells. Each junction is a circular patch studded with several hundred pores, which were produced by connexon proteins. Found in epithelia, but also in some smooth muscle and in cardiac muscle, where it is critical for the spread of excitation.

Question 38

Endocytosis

Answer 38

Material from extracellular space can be incorporated into the cell by endocytosis. The cell membrane invaginates, fuses and the newly made endocytotic vesicle buds into the cell.

Question 39

Phagocytosis

Answer 39

Bacteria or larger particulate material from extracellular space can be incorporated into the cell by phagocytosis. Bacterium binds to the cell surface receptors, triggering extensions of the cell to engulf it forming a phagosome. This binds with a lysosome carrying digestive enzyme, producing a phagolysosome.