Chapter 3: Structure and Function of the Cell

Question 1

Briefly explain the transcription in protein synthesis.

Answer 1

Transcription is transcribing the DNA into a message in a cell.

1. RNA polymerase binds to a promoter with the help of proteins called transcription factors.
2. RNA polymerase then initiates mRNA synthesis at the start codon, moves downstream along the gene in a process called elongation, synthesizing the mRNA strand as it goes. In RNA it will have Uracil instead of Thymine which is the one that pairs with Adenine in DNA.
3. Once polymerase reaches another special sequence called the terminator, then the enzyme detaches from the gene and the DNA is returned to its original state. mRNA is now produced with the information encoded in the gene.
4. After few modifications during RNA processing, the mRNA will leave the nucleus into the cytoplasm where it will find a ribosome where translation occurs.

Question 2

Explain genetic code.

Answer 2

set of rules that relate the base triplet sequence of DNA to the corresponding codons of RNA and the amino acids they specify.

Question 3

Explain nucleotide

Answer 3

it is the repeating units of nucleic acid with each consisting of a nitrogenous base, a pentose sugar, and a phosphate group.

Question 4

Explain sense strand

Answer 4

It is the strand readable on the RNA or the coding side. However, proteins involved in making RNA reads the antisense strand in order to create the sense strand for the mRNA.

Question 5

Explain antisense strand

Answer 5

It is the non-coding side strand. When making the RNA, the proteins involved in making RNA reads the antisense strand in order to make the sense strand for the mRNA.

Question 6

Explain introns

Answer 6

a segment of DNA or RNA molecule within the gene that do not code for parts of a proteins.

Question 7

Explain exons

Answer 7

a segment of DNA or RNA molecule located between regions that do code for segments of a protein.

Question 8

Explain termination

Answer 8

it is when the RNA polymerase reaches the terminator and the enzyme detaches from the transcribed RNA molecule and the DNA strand.

Question 9

Explain the difference between mitosis and meiosis.

Answer 9

Meiosis is the reproductive cell division that occurs in the gonads, it produces gametes in which the number of chromosomes is reduced by half. While mitosis is a cell division that produces two genetically identical cells, each with the same number and kind of chromosomes as the original cell.

Question 10

What are the three main parts of an animal cell?

Answer 10

Plasma membrane, cytoplasm, nucleus

Question 11

Plasma membrane

Answer 11

It forms the cell’s outer boundary and separates the cell’s internal environment from the outside environment.

It is also a selectively permeable barrier, allowing the passage of some things and not others. It also plays a role in cellular communication.

Question 12

Cytoplasm

Answer 12

It contains all the cellular contents between the plasma membrane and the nucleus.

Question 13

What is a cytosol?

Answer 13

It is the fluid portion of the cytoplasm

Question 14

Describe organelles

Answer 14

A subcellular structures embedded in the cytosol, having characteristics, shapes, and specific functions.

Question 15

Nucleus

Answer 15

large organelle that contains DNA in molecules called chromosomes

Question 16

Describe the structure of the plasma membrane.

Answer 16

Its basic structural framework is the lipid bilayer that is composed of lipid molecules such as the phospholipid (75%), cholesterol (about 20%) and glycolipids (about 5%), and lipids with attached carbohydrate groups.

Question 17

What is the function of the cholesterol in the plasma membrane?

Answer 17

it gives stability to the membrane

Question 18

What is Glycocalyx? give its 3 functions.

Answer 18

Fatty acid “tails,” which are hydrophobic hydro carbon chains

Question 19

What does selectively permeable mean?

Answer 19

Only allows the passage of some things and not others depending on some factors such as the size. Larger and polarized molecules have a great difficulty entering; therefore in need of assistance getting through.

Question 20

Give the 6 membrane proteins and give their functions.

Answer 20

1. Ion channel (Integral) - allows specific ion to move through water-filled pore.
2. Carrier (Integral) - carries specific substances across membrane by changing shape. They are also known as transporter.
3. Receptor (integral) - recognizes specific ligand and alters cell’s function in some way.
4. Enzyme (integral and peripheral) - catalyzes reaction inside or outside cell, depending on which direction the active site faces.
5. Cell-identity marker (glycoprotein) - distinguishes your cells from anyone else’s (unless you are an identical twin).
6. Linker (Integral and peripheral) - Anchors filaments inside and outside the plasma membrane, providing structural stability and shape for the cell. May also participate in movement of the cell or link two cells together.

Question 21

Describe the membrane’s fluidity.

Answer 21

Exchange, meaning shifting from position to position.

Self-sealing, has the ability to seal itself.

Question 22

Give the 5 types of gradient across the plasma membrane.

Answer 22

Concentration gradient, electrical gradient, electrochemical gradient, membrane potential, resting membrane potential

Question 23

describe what is a passive process.

Answer 23

passive processes moves down a connection gradient or electrical gradient using own kinetic energy. From high to low or from positive to negative, does not use energy or ATP.

Question 24

Describe what the principle of diffusion means and what the 5 things composing it.

Answer 24

The principle of diffusion are factors that influence the diffusion rate of substances across plasma membranes.

Those factors are the steepness of the concentration gradient, temperature, mass of diffusing substance, surface area, diffusion distance.

Question 25

Describe what a simple diffusion is.

Answer 25

A substance moves across the lipid bilayer of the plasma membrane without the help of membrane transport proteins.

Question 26

Facilitated diffusion

Answer 26

has 2 types:

1. Channel-Mediated Facilitated diffusion - a solute moves down its concentration gradient across the lipid bilayer through a membrane channel.
2. Carrier-Mediated Facilitated diffusion - needs carrier or transporter to get across the membrane

Question 27

Osmosis

Answer 27

It is a type of diffusion, and also a passive process, where there is net movement of a solvent through selectively permeable membrane. In osmosis, water likes to move where the particles are more concentrated.

Question 28

Explain the process of osmosis.

Answer 28

During osmosis, water molecules pass through a membrane via 1) phospholipid bilayer and 2) aquaporins. Osmosis only occurs when a membrane is permeable to water but not permeable to certain solutes.

Question 29

What is hydrostatic pressure?

Answer 29

it is the pressure exerted by water (liquid) on a membrane, which forces water molecules to move to either left or right until equilibrium is reached.

Question 30

What is osmotic pressure?

Answer 30

it is the pressure exerted by a fluid with impermeable solute (the higher the solute, the higher the pressure); it is the pressure needed to counteract osmosis.

Question 31

Tonicity

Answer 31

A solutions ability to change the volume of cells by altering their water content.

Question 32

Describe what is an active process.

Answer 32

• Active processes needs cellular energy to drive substances against concentration or electrical gradient (uphill) using ATP.
• Many polar or charged solutes can’t diffuse across the membrane
• low to high concentration if we wish

Question 33

What are the two sources of energy for active transport?

Answer 33

1. Primary Active Transport

- energy from hydrolysis of ATP drives solutes across the membrane