Chapter 3

Question 1

what is a cell?

Answer 1

the basic living unit of all organisms
- complex living structures
- cells have many characteristics in common but they are also specialised to perform specific functions
- highly organised unit
- the smallest units of life

Question 2

organelles

Answer 2

• within in cells
• perform specific functions
• number and type of organelles within each cell determine the cell’s specific structure and function

Question 3

nucleus

Answer 3

is a large organelle containing the cells genetic material
- genetic material is organised into 23 pairs of chromosomes which consist of DNA and proteins and coiled by chromatin
- contents of the nucleus is separated from the rest of the cytoplasm by a nuclear envelope
- nuclear envelope consists of an outer membrane and an inner membrane with a narrow space between them
- nuclear pores which are passageways through which material can move into or out of the nucleus
- nucleoli are diffuse bodies with no surrounding membrane that are found within the nucleus

Question 4

cytoplasm

Answer 4

the living material surrounding the nucleus is called the cytoplasm
- contains many types of organelles
- cytoplasm is enclosed by the cell membrane (or plasma membrane)

Question 5

Four main functions of a cell

Answer 5

1. cell metabolism and energy use
2. synthesis of molecules
3. communication
4. reproduction and inheritance

Question 6

Cell metabolism and energy use

Answer 6

the chemical reactions that occur within cells are called cell metabolism
- energy release during metabolism is used for cell activities
- examples: synthesis of new molecules, muscle contraction, and heat production

Question 7

Synthesis of molecules

Answer 7

Cells synthesise various types of molecules, including proteins, nucleic acids, and lipids.
- the different cells of the body do not all produce the same molecule
- a cells structural and functional characteristics are determined by the types of molecules the cell produces

Question 8

Communication

Answer 8

Cells produce and receive chemical and electrical signals that allow them to communicate with one another
- Example: nerve cells communicate with one another and with muscle cells, causing muscle cells to contract

Question 9

reproduction and inheritance

Answer 9

Each cell contains a copy of the genetic information of the individual
- specialised cells (sperm cells and oocytes) transmit that genetic information to the next generation

Question 10

cell membrane? function? composed of?

Answer 10

Is the outermost component of a cell
- encloses the cytoplasm and forms the boundary between material inside the cell and material outside the cell
- semipermeable meaning they allow some substances to pass in or out of the cell

Functions:
1. supporting the cell contents
2. acting as a selective barrier that determines what moves into and out of the cell
3. playing a role in communication between cells

Made up of:
- phospholipids
- proteins

Contains other molecules:
- cholesterol
- carbohydrates

Question 11

substances outside the cell are called?

Answer 11

extracellular substances

Question 12

substances inside the cell are called?

Answer 12

cytoplasmic
- cytoplasmic material has a different composition than extracellular material, and the cell’s survival depends on maintaining the difference

Question 13

Fluid-mosaic model (structure of the cell membrane)

Answer 13

• the membrane is composed of a bilayer of phospholipids and cholesterol with proteins “floating” in the membrane
• the phospholipid bilayer is the base of the cell membrane
• cholesterol within the phospholipid membrane gives it added strength and stability by limiting how much the phospholipids can move
• protein molecules “float” among the phospholipid molecules and sometimes extend from the inner to the outer surface of the cell membrane
• carbohydrates may be bound to some protein molecules, modifying their function
• membrane proteins function as membrane channels, carrier molecules, receptor molecules, enzymes, or structural supports in the membrane

Question 14

phospholipid bilayer

Answer 14

• the polar, phosphate-containing ends of the phospholipids are hydrophilic and face the extracellular fluid and cytoplasm of the cell
• the non polar, fatty acids ends of the phospholipids are hydrophobic and face away from the fluid on either side of the membrane, toward the centre of the double layer of phospholipids
• the double layer of phospholipids forms a lipid barrier between the inside and outside of the cell
• the double layer of phospholipids has a fluid quality (they are not stationary and can move a bit)

Question 15

membrane channels and carrier molecules function

Answer 15

involved with the movement of substances through the cell membrane

Question 16

receptor molecules function

Answer 16

are part of an intercellular communication system that enables cel recognition and coordination of the activities of cells

Question 17

Where are substances like enzymes, glycogen, and potassium ions found in the cell?

Answer 17

found in greater concentrations inside the cell

Question 18

Where is Na+, Ca2+, and Cl- found in the cell?

Answer 18

found in greater concentrations in the extracellular fluid

Question 19

Passive membrane transport

Answer 19

• does not require energy
• includes diffusion, osmosis, facilitated diffusion

Question 20

Active membrane transport

Answer 20

• requires energy such as ATP
• includes active transport, secondary active transport, endocytosis, and exocytosis

Question 21

what is a solution composed of

Answer 21

solutes and the solvent

Question 22

what are solutes

Answer 22

substances dissolved in a predominant liquid or gas which is called the solvent
- in constant motion
- tends to move from an area where it is in higher concentration to an area where it is in lower concentration in solution

Question 23

concentration gradient

Answer 23

is the difference in the concentration of a solute in a solvent between two points divided by the distance between the two points
- when something moves down its concentration gradient this means that the solute is diffusing from an area of higher concentration toward an area of lower concentration of that specific solute
- when it moves up (or against) this means that the substances moves from an area of lower solute concentration to an area of higher solute concentration (this requires energy)

Question 24

osmosis

Answer 24

Is the diffusion of water across a semipermeable membrane, from a region of higher water concentration to one of a lower water concentration
- though water is polar, it is small enough to pass through the phospholipid molecules or through water channels
- osmosis is important to cells b/c large volume changes caused by water movement can disrupt normal cell functions
- osmosis occurs when the cell membrane is semipermeable and a concentration gradient for water exists across the cell membrane
- water follows solutes

Question 25

osmotic pressure

Answer 25

is the force required to prevent the movement of water across a selectively permeable membrane - is a measure of the tendency of water to move by osmosis - the greater the concentration of a solution, the greater is osmotic pressure

Question 26

process of osmosis across a selectively permeable membrane

Answer 26

1. osmotic pressure can be measure by placing a solution into a tube that is closed at one end by a selectively permeable membrane and immersing the tube in distilled water 2. water molecules move by osmosis through the membrane into the tube, forcing the solution to move up the tube 3. as the solution rises, the weight of the solution produces hydrostatic pressure, which pushes water out of the tube back into the distilled water surrounding the tube. Net movement of water into the tube stops when the hydrostatic pressure in the tube cases water to move out of the tube at the same rate at which it diffuses into the tube by osmosis. The osmotic pressure of the solution in the tube is equal to the hydrostatic pressure that prevents net movement of water into the tube.

Question 27

Hypotonic solution

Answer 27

has a lower concentration of solutes and a higher concentration of water relative to the cytoplasm of the cell - the solution has less osmotic pressure than the cell - if a cell is immersed in a hypotonic solution, water moves by osmosis into the cell where the solute concentration is greater, causing the cell is swell - if the cell swells enough it will rupture, a process called lysis

Question 28

Isotonic solution

Answer 28

When a cell is immersed in an isotonic solution, the concentrations of various solutes and water are the same on both sides of the cell membrane - the cell will neither shrink or swell

Question 29

Hypertonic solution

Answer 29

solution has a higher concentration of solutes and a lower concentration of water relative to the cytoplasm of the cell - the cell will shrink or crenation

Question 30

Facilitated diffusion

Answer 30

Is a mediated transport process, involving membrane proteins such as channels or carrier proteins, to move substances across the membrane - involves the movement of substances from an area of higher concentration to an area of lower concentration - does not require ATP

Question 31

Cell membrane channels and its two channel types

Answer 31

Consist of large protein molecules that extend from one surface of cell membranes to the other - several channel types each of which allows only certain substances to pass through - characteristics of an ion or molecule determine whether it can pass through a channel - these characteristics include: size, shape, and charge Two classes of channels: 1. Leak channels - constantly allow ions to pass through 2. Gated channels - limit the movement of ions across the membrane by opening and closing

Question 32

Carrier molecules

Answer 32

Protein that extends from one side of the cell membrane to the other; binds to molecules to be transported and moves them from one side of the cell membrane to the other - moves water-soluble molecules or electrically charged ions - exhibit specificity (antibodies and receptors work effectively only on particular antigens or ligands) Function: 1. A molecule to be transported binds to a specific carrier molecule on one side of the membrane 2. The binding of the molecule to the carrier molecule in the cell membrane causes the 3-dimensional shape of the carrier molecule to change, and the transported molecule is moved to the opposite side of the cell membrane. The transported molecule is then released by the carrier molecule, which resumes its original shape and is available to transport another molecule

Question 33

Active transport

Answer 33

is a process that utilises membrane proteins to move substances across the cell membrane from regions of lower concentration to those of higher concentration, against a concentration gradient - requires ATP - it can sometimes exchange one substance for another - sodium-potassium pump moves Na+ out of cells and K+ into cells which is essential in maintaining the resulting membrane potential

Question 34

Secondary active transport

Answer 34

involves the active transport of one substance across the cell membrane, establishing a concentration gradient, which then provides the energy for moving a second substance across the membrane

Question 35

Cotransport

Answer 35

Transport of one substance across a cell membrane, could with the simultaneous transport of another substance across the same membrane in the same direction - the diffusing substances moves in the same direction as the transported substance

Question 36

countertransport

Answer 36

the diffusing substance moves in a direction opposite to that of the transported substance

Question 37

Vesicles

Answer 37

Large water-soluble molecules that cannot be transported by carrier molecules, small pieces of matter, and even whole cells can be transported across cell membranes in membrane-bound sacs called vesicles

Question 38

Endocytosis

Answer 38

is the uptake of material through the cell membrane by the formation of a vesicle - the cell membrane folds inwards to form a vesicle containing the material to be taken into the cell - the vesicle then moves into the cytoplasm - usually exhibits specificity, through the process of receptor-mediated endocytosis Steps in function: 1. the cell membrane contains specific receptor molecules that bind to certain molecules 2. when the specific molecules bind to the receptors, endocytosis is triggered. A vesicle begins to form, bringing the receptors and the bound molecules into the cell 3. The vesicles forms completely in the cytoplasm as its membrane separates from the cell membrane

Question 39

What are some molecules that can be taken into a cell by receptor-mediated endocytosis?

Answer 39

cholesterol and growth factors

Question 40

phagocytosis

Answer 40

is often used for endocytosis when solid particles are ingested - a part of the cell membrane extends around a particle and fuses so that the particle is surrounded by the membrane, that part of the membrane then pinches off to form a vesicle containing the particle - ingestion and digestion by cells of substances, such as bacteria cells, cell debris, and foreign particles - important for white blood cells to fight off infections

Question 41

Pinocytosis

Answer 41

is distinguished from phagocytosis in that much smaller vesicles are formed and they contain liquid rather than solid particles

Question 42

Exocytosis

Answer 42

is the release of substances from the cell through the fusion of a vesicle with the cell membrane

Question 43

Ribosome production

Answer 43

1. proteins produced in the cytoplasm move through the nuclear pores into the nucleus and to the nucleolus 2. These proteins are joined to ribosomal ribonucleic acid rRNA, produced within the nucleolus, to form large and small ribosomal subunits 3. The ribosomal subunits then move through the nuclear pores of the nuclear envelope into the cytoplasm 4. In the cytoplasm, one large and one small subunit join to form a ribosome during protein synthesis

Question 44

Ribosomes

Answer 44

are the organelles where proteins are produced - may be attached to other organelles - ribosomes that are not attached to other organelles are called free ribosomes

Question 45

Endoplasmic reticulum

Answer 45

a series of membranes forming sacs and tubules that extend from the outer nuclear membrane into the cytoplasm Rough ER: - ER with attached ribosomes - synthesize proteins for export from the cell Smooth ER: - ER without attached ribosomes - smooth ER is a site for lipid synthesis and detoxification of chemicals within cells - in skeletal muscle cells, the smooth ER stores calcium ions (Ca2+)

Question 46

Golgi apparatus

Answer 46

consists of closely packed stacks of curved membrane-bound sacs - it collects, modifies, packages, and distributes proteins and lipids manufactured by the ER - for example: proteins produced at the ribosomes enter the Golgi apparatus from the ER - in some cases the Golgi chemically modifies the proteins by attaching carbohydrate or lipid molecules to them, the proteins then are packages into vesicles that pinch off from the margins of the Golgi

Question 47

secretory vesicles

Answer 47

pinch off from the Golgi apparatus and move to the cell membrane - the cell membrane of a secretory vesicle then fuses with the cell membrane, and the contents of the vesicle are released to the exterior of the cell by exocytosis - secretory vesicles accumulate in the cytoplasm and are released to the exterior when the cell receives a signal

Question 48

lysosomes

Answer 48

are membrane-bound vesicles formed from the Golgi apparatus - contain a variety of enzymes that function as intracellular digestive systems Function steps: 1. Extracellular material is brought into the cell as a vesicle forms around the material 2. a lysosome forms at the Golgi apparatus 3. the lysosomes moves through the cytoplasm to the vesicle and fuses with it. the enzymes in the lysosomes are released into the vesicle 4. the lysosomal enzymes mix with the material in the vesicle, and the material is broken down

Question 49

peroxisomes

Answer 49

small, membrane-bound vesicles containing enzymes that break down fatty acids, amino acids, and hydrogen peroxide (H2O2) - hydrogen peroxide is a by-product of fatty acids and amino acid breakdown and can be toxic to a cell

Question 50

Mitochondria

Answer 50

Are small organelles with inner and outer membranes separated by space - major sites for ATP production within cells - outer membranes have a smooth contour but the inner have numerous folds called cristae - the material within the inner membrane is the mitochondrial matrix and contains enzymes and mitochondrial DNA (mtDNA) - carry out aerobic respiration

Question 51

cytoskeleton

Answer 51

is the internal framework of the cell - consists of protein structures that support the cell, hold organelles in place, and enable the cell to change shape - These protein structures are microtubules, microfilaments, intermediate filaments

Question 52

microtubules

Answer 52

hollow structures formed from protein subunits - help support the cytoplasm of cells, assist in cell division, and form essential components of certain organelles such as cilia and flagella

Question 53

microfilaments

Answer 53

are small fibrils formed from protein subunits that structurally support the cytoplasm, determining the cell shape - some are involved with cell movement

Question 54

intermediate filaments

Answer 54

are fibrils formed from protein subunits that are smaller in diameter than microtubules but larger in diameter than microfilaments - provide mechanical support the cell - specific type if keratin which is a protein associated with skin cells

Question 55

Centrsome

Answer 55

specialised area of cytoplasm close to the nucleus where microtubule formation occurs - contains two centrioles which are normally oriented perpendicular to each other - each centriole is a small cylindrical organelle composed of microtubules organised into 9 triplets - each triplet consist of 3 parallel microtubules joined together

Question 56

cilia

Answer 56

project from the surface of cells - composed of microtubules - transport mucus upward and away from the lungs

Question 57

flagella

Answer 57

structure similar to cilia but are much longer - only one per cell - propels sperm cell

Question 58

microvilli

Answer 58

specialised extensions of the cell membrane that are supported by microfilaments - increase surface area of a cell - abundant on the surface of cells that line the intestine, kidney, and other areas in which absorption is an important function

Question 59

Gene expression

Answer 59

is the process by which information stored in the genes of DNA molecules directs the manufacture of the various proteins of our cells - DNA molecule consists of nucleotides joined together to form two nucleotide strands, these two strands are connected and resemble a ladder that is twisted around its long axis - sections of these DNA strands are called genes - gene expression involves transcription and translation

Question 60

Transcription

Answer 60

occurs in the nucleus - during this process information stored in a region of the DNA is used to produce a complementary RNA molecule, called messenger RNA (mRNA) - the mRNA molecules moves to ribosomes in the cytoplasm where translation occurs - during this process, the nucleotide sequence of the molecule is used to determine the composition of a polypeptide chain, a precursor to a protein

Question 61

transcription process

Answer 61

1. DNA determines the structure of mRNA through transcription. During transcription, the double strands of a DNA segment separate 2. DNA nucleotides of the gene pair with RNA nucleotides that form the mRNA. Each nucleotide of DNA contains one of the following organic bases: thymine, adenine, cytosine, or guanine; each nucleotide of mRNA contains uracil, adenine, cytosine, or guanine. The number and sequence of nucleotides in the DNA serve as a template to determine the number and sequence of nucleotides in the mRNA. DNA nucleotides pair only with specific RNA nucleotides 3. After the DNA nucleotides pair up with the RNA nucleotides, an enzyme catalyses reactions that form chemical bonds between the RNA nucleotides to form a long mRNA segment. Once the mRNA segment has been transcribed, portions of the mRNA molecule may be removed

Question 62

Information in mRNA is carried in groups of 3 nucleotides called?

Answer 62

codons

Question 63

translation

Answer 63

is the synthesis of proteins based on the information in mRNA - occurs at ribosomes - mRNA molecule produced by transcription pass through the nuclear pores to the ribosomes - during translation a ribosome binds to an mRNA - the ribosome aligns the mRNA with tRNA molecules so that the anticodons of tRNA can pair w the appropriate codons on the mRNA - an enzyme associated with the ribosome causes the formation of a peptide bond between the amino acids bound to the tRNAs - the ribosome moves down the mRNA one codon at a time, releasing one of the tRNA and allowing the next tRNA to move into position - a peptide chain is formed - translation ends when the ribosomes reaches the stop codon on the mRNA - the polypeptide chain is released and becomes folded to form the three-dimensional structure of the protein molecule

Question 64

differentiation

Answer 64

the process by which cells develop with specialised structures and functions - some portions of DNA are active and other are inactive

Question 65

apoptosis

Answer 65

programmed cell death; a normal process by which cell numbers within various tissues are adjusted and controlled - in a developing fetus apoptosis removes extra tissue - kills dangerous cells that are infected - regulated by specific genes