Life at the Cellular level

Question 1

What is a cell and why are they small?

Answer 1

A cell is the basic unit of all life

Cells are small to:

• help with the efficiency of the cell’s absorption and waste expulsion processes
• allows fast communication from the nucleus to other organelles
• the cell can be regulated while the conditions for diffusion are still ideal
• are easier to replicate and replace when damaged

Question 2

Explain the major differences between prokaryotes and eukaryotes

Answer 2

Prokaryotic cell
–	Bacteria
–	Lack Nuclear membrane
–	No Mitochondria
–	No membrane bound structures

Eukaryotic cell
–	Human cells
–	Multicellular animals and plants
–	Nucleus with membrane
–	Membrane bound structures

Question 3

Describe cell differentiation and its role in cancer

Answer 3

Cellular differentiation is the process where a cell changes from one cell type to another. Differentiation occurs numerous times during the development of a multicellular organism as it changes from a simple zygote to a complex system of tissues and cell types. Differentiation continues in adulthood as adult stem cells divide and create fully differentiated daughter cells during tissue repair and during normal cell turnover.

In cancer cells:

• Divide with out any control, able to pass through various checkpoints in the cell cycle.
• Fail to coordinate with normal cells
• Fail to differentiate into specialized cells
• Displace and replace the normal cells if not stopped

Question 4

Describe the structures found in all cells

Answer 4

Cells are divided into 2 compartments

• Nucleus
• Cytoplasm - contains cytosol and organelles

Question 5

Define the role of the nucleus

Answer 5

Nucleus contains DNA, Nucleoprotein and some RNA

Question 6

Define the role of the nucleolus

Answer 6

The Nucleoli serve as sites for ribosomal RNA synthesis and ribosomal assembly.

Question 7

Define the role of the endoplasmic reticulum

Answer 7

Interconnecting network of membranous tubules, vesicles and flattened sacs (cisternae)

Two forms:
• Rough ER (Studded appearance due to ribosomes)
• Smooth ER

Rough ER synthesises and secretes/packages proteins

Smooth ER is responsible for lipid biosynthesis, membrane synthesis and repair

Question 8

Define the role of the ribosome

Answer 8

Protein factories of the cells

Minute cytoplasmic organelles with 2 subunits.

Question 9

Define the role of the golgi apparatus

Answer 9

• Stack of flattened vesicles which package and process secretory proteins.
• Also synthesise complex polysaccharides

Question 10

Define the role of the lysosome

Answer 10

• Membrane bound organelles
• Act as cellular stomachs
• Contain amorphous granular materials which are used to break down bacteria and debris.

Question 11

Define the role of the peroxisome

Answer 11

Small membrane bound organelles
Contain enzymes:

• Catalase – Regulates hydrogen peroxide conc.
• Oxidases – Involved in Beta-oxidation of long chain fatty acids

Question 12

Define the role of the mitochondrion

Answer 12

Mobile, cigar shaped organelles
• Permeable outer membrane containing porin
• Folded inner membrane – Cristae
• Filled with amorphous matrix
• Needed for oxidation + Krebs Cycle

Question 13

Define the role of the flagellum and cilia

Answer 13

Cilia and eukaryotic flagella are both made of microtubules

o Cilia—short, usually many present, move with stiff power stroke and flexible recovery stroke. For example, cilia line the bronchus to remove microbes and debris from the lungs.
o Flagella—longer, usually one or two present, movement is snakelike. E.g. enables motility in sperm.

Question 14

Describe the structure and function of the plasma membrane

Answer 14

The cell membrane is made up of a phospholipid bilayer.
o They are Dynamic (constantly formed and maintained, or dismantled and metabolised depending on needs of cell.
o Very flexible due to fatty acids (may rupture if over stretched)
o Insulators (hydrophobic hydrocarbon tails)

Functions
• Selective barrier
• Detects chemical messengers and signalling molecules from surrounding cells or other organs
• Contains membrane proteins (some span the membrane, others are embedded in the membrane) e.g. integral or peripheral

Question 15

Define the role and constituents of the cytoskeleton

Answer 15

This provides strength and support, while also allowing for cell motility.

o Microfilaments – Fine strands of actin ( G and F actin subunits also found in non-contractile cells). In small intestine, Microfilaments form Microvilli.
o Microtubules - Larger than microfilaments, can form cilia (9 pairs of microtubules)

Question 16

Define the 10 major elements used to construct human biomolecules.

Answer 16

O, H, C, N, Na, Cl, K, Ca, S, P

Question 17

State the importance of chemical functional groups and molecular configuration and conformation in determining biomolecular function

Answer 17

Functional groups can affect how the molecule acts around others. E.g. OH groups allow for H bonds and soulubility in water. S groups allow di-sulphide bridges.

Configuration – The fixed arrangement of atoms in a molecule eg. Cis/Trans

Conformation – The precise arrangement of atoms in a molecule (free rotation etc.)

Question 18

List and give examples of the five kinds of chemical reaction occurring in living organisms.

Answer 18

1) Redox Reactions – Usually 2 electrons are gained or lost.
Eg. Glycolysis in muscles – Glucose -> Pyruvate -> Lactate

2) Making/breaking C-C bonds
Eg. Cleavage of Glucose in Glycolysis

3) Internal Rearrangements
Eg. Glucose-6-Phosphate -> Fructose-6-Phosphate in Glycolysis

4) Group Transfers
Eg. Transfer of phosphate groups in glycolysis

5) Condensation/Hydrolysis
Eg. Formation and breaking of nucleic acids and proteins by condensation and hydrolysis reactions respectively.

Question 19

Describe the general structures of nucleic acids

Answer 19

DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are polymers of nucleotides linked in a chain through 3’,5’ phosphodiester bonds.

A nucloetide = base + sugar + phosphate

There are 2 kinds of base in nucleic acids
– Pyrimidines (flat, single rings) – CTU
– Purines (flat, double rings) – AG

Question 20

Briefly describe life processes in terms of the Laws of Thermodynamics.

Answer 20

Energy can be converted from one form to another, but not created or destroyed.
All energy transformations ultimately lead to more entropy in the universe.
This is true for living organisms, even though the processes create more order, the heat created is released into the universe, creating more entropy

Question 21

Define metabolism, catabolism and anabolism, and describe, in outline, how they are interdependent.

Answer 21

Metabolism – The chemical processes in a living organism that allows food to be used for tissue growth. It is a mix of summative and degradative reactions (anabolism and catabolism respectively.)

Catabolism – Occur with -ve free energy, are spontaneous.

Anabolism- Occur with +ve free energy, are not spontaneous.

Energy obtained from catabolic reactions, is used up in anabolic reactions to produce more highly ordered compounds.

Question 22

Describe, in general terms, the structures and contributions to metabolic flow of ATP, ADP, NADP, NAD, FAD.

Answer 22

ATP/ADP acts as a free energy carrier, coupling anabolic and catabolic reactions using phosphate group transfers.

NADP/NAD and FAD are used in redox reactions as electron carriers.

Question 23

Define the general structures of polysaccharides

Answer 23

These are polymers of sugar monomers linked by glycosidic bonds (1-6 for straight, 1-4 for branches). Following all made from D-glucose:

Cellulose - very straight
Starch - branched
Glycogen - highly branched

Question 24

Define the general structure of lipids

Answer 24

Usually contain one or more long-chain fatty acid, which can either be saturated or non-saturated (ratios determine viscosity)

There are several classes of lipids, including:

Triacylglycerides/triglycerides
•	Storage lipids, “fat”
•	Non-polar
•	3 fatty acid chains linked to glycerol
Phospholipids
•	Similar to triglycerides,
•	Have ‘head’ group attached to glycerol
•	Polar

Question 25

Describe different types of stem cells

Answer 25

Multipoint - Cells that can differentiate into many cell types
Pluripotent - can differentiate into all cell types of the body
Totipotent - can make cells found in all the body, plus embryonic or placental cells.

Inner cell mass of blastocysts is also a source of embryonic stem cells. The blastocyst is a structure formed in the early development of mammal

Question 26

Describe apoptosis

Answer 26

Programmed cell death

Biochemical events lead to characteristic cell changes (morphology) and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, chromosomal DNA fragmentation, and global mRNA decay.

Question 27

Describe 6 plasma membrane functions

Answer 27

Transport
Intercellular joining
Enzymatic activity
Cell-cell recognition
Site for receptors
Attach to cytoskeleton and ECM

Question 28

Describe endocytosis and exocytosis

Answer 28

Endocytosis is a form of active transport in which a cell transports molecules (such as proteins) into the cell. Endocytosis and its counterpart, exocytosis, are used by all cells because most chemical substances important to them are large polar molecules that cannot pass through the hydrophobic plasma or cell membrane by passive means.

Exocytosis is a form of active transport in which a cell transports molecules (such as proteins) out of the cell

Question 29

Describe some cell adhesion molecules and their functions

Answer 29

Tight junctions - create a physical barrier to diffusion across layers of cells, seals gaps between cells to make an impermeable barrier

Gap junctions - channels linking the cytoplasm of two cells together to allow cell communication or signal transduction e.g. connexins

Adhesive junctions – includes adherens junctions, desimsomes and hemidesmisomes, which transmit stress through tethering to cytoskeleton are cell–cell or cell–matrix. Adherens junctions are defined as a cell junction where the cytoplasmic face is linked to the actin cytoskeleton

Question 30

Describe different methods of cell signalling

Answer 30

Contact dependent – does not require release of a signaling molecule, but instead uses direct physical contact between signaling molecules in the plasma membrane of one cell and receptors in the plasma membrane of the target cell.

Paracrine - is a form of cell-cell communication in which a cell produces a signal to induce changes in nearby cells, altering the behavior or differentiation of those cells.

Synaptic/neuronal - form of long distance signaling delivered quickly and specifically through the axons and nerve terminals of the neuron, using action potentials and neurotransmitters.

Endocrine - a hormone signaling molecule is released in the bloodstream to send a signal throughout the entire body.