Week 5 - Cell Structure & Function

Question 1

What 5 key features characterize living organisms?

Answer 1

Living organisms are characterized by:

1. cell membranes
2. metabolic processes
3. genetic material (DNA)
4. the ability to grow and reproduce
5. responses to environmental stimuli.

Question 2

What is the significance of protocell membranes in early life forms?

Answer 2

Protocell membranes allowed for compartmentalization, enabling distinct biochemical processes, such as ATP production and photosynthesis, which contributed to the early evolution of life and the alteration of Earth’s atmosphere

Question 3

What distinguishes prokaryotic cells from eukaryotic cells?

Answer 3

Prokaryotic cells are simpler, lack a nucleus, and have DNA in a nucleoid region. Eukaryotic cells are more complex, containing a membrane-bound nucleus and various organelles that perform specialized functions

Question 4

What are the main points of cell theory? (3)

Answer 4

Cell theory states that:

All living organisms are composed of one or more cells.
The cell is the basic unit of life.
All cells arise from pre-existing cells.

Question 4

Describe the basic structure of cell membranes:

Answer 4

Cell membranes are composed of a lipid bilayer containing proteins, carbohydrates, and cholesterol, which provide structural integrity and facilitate communication and transport

Question 5

What is the role of ribosomes in a cell?

Answer 5

Ribosomes are responsible for synthesizing proteins by translating messenger RNA (mRNA) into amino acid sequences, either free in the cytoplasm or bound to the endoplasmic reticulum

Question 6

How do light microscopes enhance cellular visualization?

Answer 6

Light microscopes utilize glass lenses to magnify specimens using visible light, allowing for the observation of cellular structures at resolutions up to 200 nm, though they cannot visualize viruses

Question 7

What are the functions of the endoplasmic reticulum (ER)?

Answer 7

1. The rough ER synthesizes proteins
2. while the smooth ER is involved in lipid synthesis and detoxification processes.
3. Both types of ER are continuous with the nuclear envelope.

Question 8

From smallest to biggest cell size:

Answer 8

Bacteria is the smallest, then
yeast,
RBC,
ferns,
nitella (algae)

Question 9

Explain the process of ATP synthesis in mitochondria

Answer 9

ATP synthesis in mitochondria occurs during oxidative phosphorylation, where a proton gradient is created by electron transport. Protons flow back into the mitochondrial matrix through ATP synthase, generating ATP.

Question 10

Describe the structure and function of chloroplasts:

Answer 10

Chloroplasts have a double membrane and contain thylakoid membranes stacked in grana, where photosynthesis occurs. They convert CO₂ and water into sugars using light energy, facilitated by chlorophyll

Question 11

What is the role of peroxisomes in cellular metabolism?

Answer 11

Peroxisomes are involved in the oxidation of fatty acids and the breakdown of hydrogen peroxide using catalase, helping to detoxify harmful byproducts of metabolism

Question 12

How do nuclear pores regulate material transport?

Answer 12

Nuclear pores are selective channels in the nuclear envelope that allow certain proteins and RNA molecules to enter or exit the nucleus, thus controlling the flow of genetic information

Question 13

What happens during DNA replication prior to cell division?

Answer 13

During DNA replication, the double helix unwinds, and each strand serves as a template for synthesizing new complementary strands, resulting in two identical DNA molecules for daughter cells.

Question 14

What types of plastids exist, and what are their functions?

Answer 14

Types of plastids include
1. chloroplasts (for photosynthesis),

2. amyloplasts (for starch storage),
3. chromoplasts (for pigment synthesis)

Question 15

What distinguishes transmission electron microscopy (TEM) from scanning electron microscopy (SEM)?

Answer 15

TEM involves passing electrons through a thin sample (70-100 nm) to create detailed internal images, requiring staining with heavy metals.

In contrast, SEM scans a beam of electrons across the sample surface, capturing the topography and composition in black and white, focusing on surface details rather than internal structures.

Question 16

What are the typical resolutions achieved by electron microscopes?

Answer 16

Electron microscopes can achieve resolutions below 0.5 nm. TEM can resolve structures with a wavelength of 0.004 nm and a resolution of 0.05 nm, making them about 4000 times more powerful than light microscopes.

Question 17

8. Describe the three molecular-level techniques used for localizing specific molecules:

Answer 17

Fluorescent Dyes: These dyes bind to DNA or cellular components, allowing visualization under specific light conditions.

Immunocytochemical Labeling: Antibodies are used to bind specific proteins; the attached fluorescent markers allow visualization of these proteins within cells.

Genetic Tagging with Fluorescent Proteins: This involves fusing genes encoding fluorescent proteins to target genes, enabling the production of fluorescent-tagged proteins for observation under a light microscope.

Question 18

9. How did fluorescent genetic tagging contribute to cystic fibrosis research?

Answer 18

Researchers used fluorescent genetic tagging to locate the CFTR protein responsible for cystic fibrosis. This technique allowed them to confirm the protein’s location and functionality on the apical surface of epithelial cells, providing insights into the disease’s mechanism.

Question 19

4. Describe the process of physical sectioning in microscopy:

Answer 19

Physical sectioning involves slicing samples into thin sections (1-5 nm thick) to allow light to pass through

Techniques include manual sectioning with a blade, using a microtome, or cryosectioning (freezing the sample before slicing)

Embedded samples in wax can also be sectioned using diamond or glass knives

Question 20

What are the advantages of confocal microscopy?

Answer 20

Confocal microscopy uses a laser to illuminate samples and a pinhole to filter out out-of-focus light, allowing for high-resolution, 3D imaging of thick samples

This technique enables researchers to observe dynamic changes in subcellular organizations at various depths within the sample

Question 21

What do we need to get a good image?

Answer 21

1. Magnification = the ratio/enlargement of image size to actual size
2. Resolution = minimum distance between two distinguishable points
3. Contrast = visible differences in the parts of the sample

Question 22

Orienting to the issue - 3 types of cuts:

Answer 22

Longitudinal section
Paradermal section
Transverse cross section

Question 22

What is the 5 step process for cell division?

Answer 22

Dna replication
Sort and align chromosomes
Chromosomes separate
The cytoplasm divides (cytokinesis)
The result is two genetically identical daughter cells (diploid)

Question 23

How are chromosomes arranged when NOT in cell division?

Answer 23

Chromosomes are almost fluid, not tightly woven in shapes
Easily move and reorganise themselves when not undergoing cell division

Question 24

What is evidence for mitochondria being from endosymbiosis?

Answer 24

1. Mitochondria have their own DNA and ribosomes, and can make their own proteins

Evidence: mitochondria is circle shaped = similar to bacterial DNA and ribosomes are more similar to bacterial ribosomes

Mitochondria and nucleus both have a DOUBLE MEMBRANE

Question 25

What are the 5 major things within a chloroplast?

Answer 25

1. Envelope = double membrane
2. Thylakoid membranes = folded system of internal membranes, contains RuBisCO
3. RuBisCO = most abundant protein on earth, helps with C02 reactions, ATP
4. Grana = forming stacks of internal membranes
5. Stroma = chloroplast matrix

Question 26

What type of image does TEM typically produce?

Answer 26

A) Surface detail images
B) Internal structural images
C) 3D images
D) Color images
Answer: B) Internal structural images

Question 27

Which type of microscope uses a laser to scan samples?

Answer 27

A) Light microscope
B) Transmission electron microscope
C) Scanning electron microscope
D) Confocal microscope
Answer: D) Confocal microscope

Question 28

What is a key characteristic of scanning electron microscopy?

Answer 28

A) Uses transmitted light
B) Provides high-resolution internal images
C) Examines surface topography
D) Requires staining with heavy metals
Answer: C) Examines surface topography

Question 29

What is the purpose of using heavy metals in TEM?

Answer 29

A) To improve contrast by blocking electrons
B) To enhance color in images
C) To strengthen the sample
D) To prevent contamination
Answer: A) To improve contrast by blocking electrons

Question 30

What is the resolution of a typical electron microscope?

Answer 30

A) 200 nm
B) 0.5 nm
C) 5 nm
D) 50 nm
Answer: B) 0.5 nm