Cell theory 1

Question 1

What are the possible spots for accumulation of complex C-compounds and life formation?

Answer 1

hot springs (terrestrial) and hydrothermal vents (ocean)

Question 2

Prebiotic period vs period after the first life conditions (O2, CO2, CH4, UV radiation levels, temperature, natural disasters)

Answer 2

prebiotic: low, high, high, high (no ozone layer), high (greenhouse gases), intense meteorite bombardment and frequent lightning storms, after: increased, everything else decreased

Question 3

Exceptions to the general definition of life

Answer 3

1| Mature erythrocytes (no nucleus, no DNA)
2| Aseptate fungal hyphae (continuous rows of fused cells)
3| Mule (sterile, reproduction impossible)

Question 4

Steps the life (1st cell) formation

Answer 4

1| Inorganic into simple organic compounds, Miller-Urey experiment (primordial soup)
2| Simple organic compounds (monomers) into polymers (mixture of monomers on hot clay, rocks, sand -> polymers)
3| Spontaneous formation of plasma membrane (coalescence of phospholipids) around the cell
4| Self-replicating molecules (basis of inheritance)

Question 5

Why is RNA the presumed first genetic material (benefits vs weakness)

Answer 5

capable of both storing genes and self-replication without enzymes (unlike DNA) – some types of RNA can act as catalysts
however has less storing capacity than DNA and is more often subject to mutations

Question 6

LUCA

Answer 6

the most recent population from which all (eukaryotic) organisms on Earth share a common descent

Question 7

What is the evidence for the existence of LUCA

Answer 7

1| The universality of genetic code
2| All life shares a common mechanism of transcription and translation
3| Certain genes are distributed across all organisms (e.g. instructions for DNA replication)

Question 8

Approaches used to estimate the dates of the 1st cells and LUCA (because microbes don’t leave fossils)

Answer 8

biochemical evidence and phylogenetic comparison

Question 9

Describe biochemical evidence (first evidence of life)

Answer 9

chemicals produced by cellular processes that provide evidence of past or present life. The earliest evidence of life dates to 3.42 billion years ago in the form of stromatolites (layers of sediment laid down by microbes, Australia) – LUCA near hydrothermal vents (genomic analysis) genes proposed to belong to LUCA are involved in the use of H2 as an E source

Question 10

Describe phylogenetic comparison (LUCA)

Answer 10

comparing the genome (genomic sequences) of different species to develop a timeline for evolutionary divergence – the number of differences between the genomes of two species is proportional to the time since they diverged from a common ancestor. Scientists established the original LUCA genome by searching for genes present in both prokaryotic domains (bacteria and archaea) - 355 genes are proposed to have originated directly from LUCA

Question 11

What is the molecular clock (example)?

Answer 11

the estimated time of evolutionary divergence using genomic comparisons (the mutation grade of DNA/RNA/proteins) based on the assumption that there is a direct correlation between the number of sequence differences and the time since two species diverged, e.g. if a gene mutates at 1 base pair per 100 000 years rate and 2 species have 6 differences in a gene sequence, divergence occurred 600 000 years ago

Question 12

When did LUCA’s evolution into archaea and bacteria happen?

Answer 12

at any point between 2 to 4 billion years ago – based on phylogenetic comparisons and the molecular clock

Question 13

What is magnification?

Answer 13

the number of times an object is magnified (how much smaller/larger is the image than the real specimen). As magnification increases, FOV decreases

Question 14

How is magnification calculated?

Answer 14

(image size)/(actual size)

Question 15

What is resolution?

Answer 15

the ability of a microscope to show two close objects separately, depends on the wavelength of the rays that pass through the spectrum (e- have a shorter wavelength so EM has a higher resolution)

Question 16

What is the scale bar?

Answer 16

a line added to the micrograph to show the actual size of the structure

Question 17

Compare LM and EM (what passes through the specimen, FOV, magnification, resolution, colors, type of specimen)

Answer 17

LM: beam of light, larger, up to 500x, 0.25 microm apart, visible, alive
EM: beam of electrons, smaller, up to 500 000x, 0.25 nanom apart, black-white, dead

Question 18

What are the two types of EM?

Answer 18

TEM (transmission electron microscope) for the interior and SEM (scanning electron microscope) for the surface of cells

Question 19

Freeze-fracture EM

Answer 19

physically breaking apart frozen biological samples through the weakest point of the cell – structural details exposed by the fracture plane are visualized by deposition of Pt-C to make a replica for examination in the EM

Question 20

Cryogenic EM

Answer 20

structures of proteins, nucleic acids, and other biomolecules – studying how they move around and change as they perform their functions (alive)

Question 21

Cell theory

Answer 21

1| Cells are the basic units of life (nothing smaller than the cell can survive independently)
2| All living things consist of cells
3| New cells come from pre-existing cells by the process of cell division

Question 22

Discrepancies (exceptions) to the cell theory

Answer 22

1| Striated (skeletal) muscles – more than 1 nucleus per cell – long cells, around 30 mm
2| Giant algae, Actabularia – single-celled organism but up to 20 cm long
3| Aseptate Funghi – fungal hyphae (narrow thread-like structures) are made up of rows of cells usually separated with septa but some funghi lack this septa (multinucleated)

Question 23

Functions of life

Answer 23

metabolism, response, nutrition, excretion, reproduction, growth, homeostasis, movement

Question 24

How did anucleate and multinucleated adapt their structure to fit their function?

Answer 24

anucleate cells don’t have a nucleus (cannot transcribe DNA to make mRNA and synthesize proteins – erythrocytes to have more space for Hb to carry more O2) and multinucleate cells have multiple nuclei (more mRNA and proteins), e.g. skeletal muscle/aseptate fungi

Question 25

Common features and differences in prokaryotic and eukaryotic cells

Answer 25

common: plasma membrane, cytoplasm, DNA and ribosomes present
differences: size (eukaryotic much larger) and complexity (eukaryotic cells are compartmentalized (many differences arise from this fact like type of cell division, DNA structure…))

Question 26

All components of a prokaryotic cell

Answer 26

cell wall, plasma membrane, nucleoid, mesosome, thylakoids, pili, plasmoid, cytoplasm, flagellum, 70S ribosomes, capsule

Question 27

All components of a eukaryotic cell

Answer 27

cell wall (plant), plasma membrane, nucleus, chloroplast (plants), cilia, cytoplasm, flagella, 80S ribosomes, rough and smooth endoplasmic reticulum, Golgi apparatus, vesicles (lysosomes in animal, vacuole in plant), mitochondria, microtubules and microfibrils (cytoskeleton)

Question 28

Binary fission

Answer 28

means of asexual reproduction in prokaryotes, phospholipids get added to the existing plasma membrane, and the offspring produced is genetically identical to the parent cell, in ideal conditions happens every 20 minutes

Question 29

Cell wall function

Answer 29

provides shape, and allows the cell to withstand turgor pressure without bursting, the principal component of prokaryotic cell wall is peptidoglycan, of fungi chitin, and of plant cells cellulose

Question 30

Plasma membrane function

Answer 30

controls transport in/out of the cell (endocytosis and exocytosis), composed of phospholipids and proteins

Question 31

Nucleoid vs plasmoid

Answer 31

nucleoid is the region where circular, naked prokaryotic DNA is situated and a plasmoid is additional genetic info of the cell and it promotes variation

Question 32

Mesosomes

Answer 32

infoldings of the plasma membrane, it is the site of CR

Question 33

Pilli vs flagellum

Answer 33

pilli used for adhesion to the surface and in bacterial conjugation (sexual reproduction by the exchange of DNA between cells) and flagellum is a thread that moves the cell by propelling it through its aqueous environment

Question 34

Cytoplasm function

Answer 34

also called cytosol, it is a fluid substance and the site of all metabolic reactions (contains enzymes that catalyze many metabolic reactions)

Question 35

How are eukaryotic cells more complex than prokaryotic?

Answer 35

they are compartmentalized with internal membranes, meaning that they have organelles (each is specialized for a certain function)

Question 36

What are the advantages of being compartmentalized

Answer 36

1| pH, enzyme, and substrate levels can be kept at optimal levels for each specific process happening inside the cell (processes cannot intervene with each other)
2| Free radicals (mitochondria), peroxide, and other strong oxidizing agents cannot intoxicate/damage other parts of the cell
3| Organelles can be moved around the cell (mitochondria for example)

Question 37

Nucleus structure and function

Answer 37

the largest and heaviest organelle (animal) that controls the process of gene expression – it is surrounded by a nuclear membrane (phospholipid bilayer) with nuclear pores, contains nucleoplasm (= nucleolus + chromatin) – nucleolus contains densely packed DNA + RNA + proteins and chromatin 46 uncoiled DNA molecules associated with histones

Question 38

rER vs sER function (plus rER structure)

Answer 38

has a single membrane and is made out of cisternae (flattened membrane sacs) – it has bound ribosomes on cisternae – rER function is to refine proteins by giving them quaternary structure (prosthetics…) and sER function is the production of carbohydrates are lipids

Question 39

Golgi apparatus structure and function

Answer 39

made our of cisternae shorter and more curved than those in ER and has no ribosomes bound – its function is the final modification/refinement of proteins created in ER (packed into vesicles)

Question 40

Vesicles function and examples (plant and animal)

Answer 40

organelles with a single membrane with fluid inside which can be formed as a result of budding of GA or after endocytosis – e.g. in animals are usually non-permanent and small like lysosomes (lysozyme which is used in the internal digestion of damaged cells) and peroxisomes (catalase), and permanent and larger in plants like vacuole (largest organelle in plant cells, stores water and other juices with dissolved compounds (nicotine in tobacco)