Life at a cellular level

Question 1

What is a cell?

Answer 1

• The cell is the functional unit of all living things.

Question 2

Why are cells small?

Answer 2

• Smaller cells = larger surface area to volume ratio. This allows for gas exchange to happen more easily. Diffusion becomes easier.

Question 3

What are stem cells?

Answer 3

• Stem cells are cells that can differentiate into many cell type (multipotent) or all cell types of the body (pluripotent)

Question 4

What is cell differentiation?

Answer 4

• Cell differentiation: cells pass through a series of changes during development -> changes in gene expression is reflected in the alteration of cell structure and behavior.
  - > cell fusion is where small number of cell types undergo a process of cell fusion as part of their normal differentiation.

Question 5

How are cancer cells formed? (really really simply version)

Answer 5

• Cancer cells: divide with out any control, they fail to coordinate with normal cells and fail to differentiate into specialized cells. Cancer cells displace and replace normal cells if not stopped.

Question 6

How is the cell membrane involved in cellular transport?

Answer 6

• Cell membrane (plasma membrane) are selective barriers that detect chemical messengers and signaling molecules from surrounding cells or other organs.

Question 7

What is passive diffusion?

Answer 7

• Passive transport moves across a concentration gradient, or a gradual difference in solute concentration between two areas.
• Concentration gradient needed
• Lipid soluble molecules pass freely (non polar)

Question 8

What is facilitated diffusion?

Answer 8

-Facilitated diffusion (also known as facilitated transport or passive-mediated transport) is the process of spontaneous passive transport (as opposed to active transport) of molecules or ions across a biological membrane via specific transmembrane integral proteins.

• Concentraion gradient needed
• Requires carrier molecules

Question 9

What is endocytosis?

Answer 9

the taking in of matter by a living cell by invagination of its membrane to form a vacuole.

Question 10

What is exocytosis?

Answer 10

a process by which the contents of a cell vacuole are released to the exterior through fusion of the vacuole membrane with the cell membrane.

Question 11

What are the features of the mitochondria? (4)

Answer 11

• outer membrane contains pores
• Inner membrane has cristae
• Matrix contains binding sites for calcium and also most of the enzymes for oxidation of food molecules
• They have their own circular DNA, ribosomes (similar to bacterial ribosomes), they synthesise most of their own proteins and they self replicate

Question 12

What are the features of the nucleus? (4)

Answer 12

• Contains DNA nucleoprotein and some RNA
• Nucleoli are sites of ribosomal RNA synthesis and ribosomal assembly
• DNA tends to be one of two forms – heterochromatin or euchromatin
• Nuclear membrane (envelope) contains a phospholipid bilayer, encloses the nucleus, contains pores and is closely associated with the endoplasmic reticulum.

Question 13

What is the rough endoplasmic reticulum?

Answer 13

Rough endoplasmic reticulum: Is membrane bound, has ribosomes attached, protein modifications and transport coordinated by the RER and golgi apparatus.

Question 14

What is the smooth endoplasmic reticulum?

Answer 14

Smooth endoplasmic reticulum: Is used mainly to break down compounds (e.g drugs and glycogen) or synthesise compounds (e.g lipids) (mainly used for breakdown)

Question 15

What are lysosomes?

Answer 15

Lysosomes: Used to separate enzymes from the rest of the cell – used in autophagy (digestion of cells own materials) or digestion of engulfed particles (e.g bacteria)

Question 16

What are the 6 membrane functions?

Answer 16

1) transport
2) Enzymatic activity
3) Receptors for signal transduction
4) Intercellular joining
5) Cell-cell recognition
6) Attachment to the cytoskeleton and extracellular matrix

Question 17

How does the membrane carry out its function of transport?

Answer 17

Transport – protein spans the membrane which may provide a hydrophilic channel across the membrane that is selective for a particular solute – some transport proteins hydrolyze ATP as an energy source to actively pump substances across the membrane.

Question 18

How does the membrane carry out its function of enzymatic activity?

Answer 18

Enzymatic activity – Protein built into the membrane may be an enzyme with the active site exposed to substances in the adjacent solution. – in some cases enzymes in membrane act as a team that catalyze sequential steps of a metabolic pathway.

Question 19

How does the membrane carry out its function of receptors for signal transduction?

Answer 19

Receptors for signal transduction – membrane protein exposed to the outside of the cell may have a binding site with a specific shape that fits the shape of a chemical messenger such as a hormone. External signal may cause a conformational change in the protein that indicates a chain of chemical reactions in the cell

Question 20

How does the membrane carry out its function of intercellular joining?

Answer 20

Intercellular joining – Membrane proteins of adjacent cells may be hooked together in various kinds of intercellular junctions. Some membrane proteins (CAMs) of this group provide temporary binding sites that guide cell migration and other cell to cell interactions.

Question 21

How does the membrane carry out its function of cell-cell recognition?

Answer 21

Cell-cell recognition – Some glycoproteins serve as identification tags that are specifically recognized by other cells

Question 22

How does the membrane carry out its fuction of ‘attachment to the cytoskeleton and extracellular matrix’?

Answer 22

• Attachment to the cytoskeleton and extracellular matrix – Elements of the cytoskeleton and the extracellular matrix may be anchored to membrane proteins which help maintain cell shape and fix the location of certain membrane proteins. Others play a role in cell movement or bind adjacent cells together.

Question 23

What are the 5 roles of the cytoskeleton?

Answer 23

• Supports and maintains cell shape
• Holds organelles in position
• Moves organelles
• Involved in cytoplasmic streaming
• Interacts with extracellular structures to hold cell in place

Question 24

The cytoskeleton is made up of 3 different types of filament, what are they?

Answer 24

1) microfilament
2) Intermediate filament
3) Microtubules

Question 25

What are microfilaments?

Answer 25

Microfilament – made up of strands of the protein actin, often interact with strands of other proteins

Question 26

What are intermediate filaments?

Answer 26

Intermediate filaments – made up of fibrous proteins organized into tough, rope like assemblages that stabilize a cell’s structure and help maintain its shape

Question 27

What are microtubules?

Answer 27

• long hollow cylinders made up of many molecules of the protein tubulin. Tubulin consists of two subunits, alpha-tubulin and beta-tubulin

Question 28

What are the 4 types of junctions?

Answer 28

1) occluding junction
2) cell-cell anchoring junctions
3) Channel-forming junctions
4) Cell-matrix anchoring junctions

Question 29

What are tight junctions?

Answer 29

• create physical barrier to diffusion across layers of cells - Dependent on calcium

Question 30

What are Adhesive junctions? (2 sub-types)

Answer 30

1) Adherens junctions - link actin filaments between two different cells
2) Desmosomes - link keratin filaments in two different cells

Question 31

What are gap junctions?

Answer 31

Channels linking two cell cytoplasm together

Question 32

What are the 4 features of a prokaryotic cell?

Answer 32

• Bacterial cell
• Lack nuclear membrane
• No mitochondria
• No membrane bound structures

Question 33

What are the 4 features of Eukaryotic cells?

Answer 33

• Human cells
• Multicellular animals and plants
• Nucleus with membrane
• Membrane bound structures