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MCAT - Systems (Biology) > The Cell > Flashcards

The Cell Flashcards

1
Q 
What are most taxonomical classification systems based upon?
So what can you conclude about any two animals from the same class for example?
A

Based upon genetic similarity resulting from shared phylogeny, or evolutionary history.
So all mammals likely share a common genetic ancestor.

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2
Q

What is a likely mechanism of mitochondria evolution?

A

From a symbiotic relationship btwn aerobic prokaryotes and eukaryotes.

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3
Q

What is the cell wall of bacteria made of? (detail)

A

Peptidoglycan.

- consists of a series of disaccharide polymer chains with AAs. The chains are attached by an interbridge of more AAs, or via their own AAs.
* these crosslinks are targeted by antibiotics(ie, penicillin) --> which disrupts the cell wall, lyses the cell and kills bacterium
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4
Q

How can bacteria be classified?

A

via Gram Staining.

gram-negative: thin peptidoglycan cell wall located btwn its two plasma membranes

     - appear pink
     - permeability: outer membrane > inner membrane
     - has lipopolysaccharides-- works as protective barrier from Abs and antibiotics

gram-positive: thick peptidoglycan cell wall
- appears purple (bc thickness doesn’t let stain leak out)

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5
Q

What is the space btwn the cell wall and the plasma membrane?
What does it conatin?

A

Periplasmic space.

Contains proteins that help the bacteria acquire nutrition (eg, hydrolytic enzymes)

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6
Q

What some basic differences between prokaryotes and eukaryotes?
**

A

• Presence of complex membrane-bound organelles (they have things like smaller ribosomes though to translate proteins)
• Membrane-bound Nucleus:
- instead of a nucleus, proks have a single circular double stranded molecule of “naked” DNA. This joins with RNA and proteins to form a Nucleoid.
- euks have DNA coiled with histone proteins.
• Mitotic Division vs Binary Fission

Proks: mRNA does not undergo post-translational modifications.
Euks: mRNA undergoes splicing, addition of Pol-A tail and 5’ cap

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7
Q

What is Flagellar Propulsion on a gram-negative bacteria used for?

A

Flagellar Propulsion

  • long, hollow, rigid cylinders made from flagellin protein
  • rotate counterclockwise to propel bacterium in a single direction
  • rotate clockwise to make bacterium tumble (change orientation)
  • uses proton gradient energy
  • directed movement toward substances that will promote survival and growth = Chemotaxis
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8
Q

Bacteria do not undergo mitosis or meiosis, instead they undergo what?
Explain the process.

A

Binary Fission.

  • 2 DNA Pols begin at ORI on circle and move in opposite directions, making complementary DNA double stranded circles
  • the cell then divides resulting in 2 genetically identical daughter cells
  • exponential growth
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9
Q

Explain Conjugation

A
  • CONJUGATIVE plasmid (possesses gene for sex pilus) transferred via sex pilus
  • Can transfer an F plasmid = fertility factor because it codes for the sex pilus. A bacteria with the F factor is called F+, one without is F-
    - F factor can be in the form of an episome (=integrated in chromosome)
  • Can transfer the R plasmid: donates resistance to antibiotics.
    • if you prescribe multiple antibiotics at same time, you can develop super-bacterium which contain antibiotic resistances on 1+ R plasmids
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10
Q

What does it mean that a plasmid is extragenomic DNA?

A

= replicate independently from nuclear DNA

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11
Q

What is the cell wall of bacteria made of? (detail)

What are eukaryotic cell walls made of (if any)?

A

Peptidoglycan.

- consists of a series of disaccharide polymer chains with AAs. The chains are attached by an interbridge of more AAs, or via their own AAs.
* these crosslinks are targeted by antibiotics(ie, penicillin) --> which disrupts the cell wall, lyses the cell and kills bacterium

Euks: if plants = cellulose. If fungi= chitin

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12
Q

Explain Transduction

A

transfer of genetic material by a virus. Capsid of a virus mistakenly encapsulates host cell DNA instead of its own

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13
Q

What is Flagellar Propulsion on a gram-negative bacteria used for?

What are flagella made of in Euks?

A

Flagellar Propulsion

  • long, hollow, rigid cylinders made from Flagellin protein
  • rotate counterclockwise to propel bacterium in a single direction
  • rotate clockwise to make bacterium tumble (change orientation)
  • uses proton gradient energy
  • directed movement toward substances that will promote survival and growth = Chemotaxis

Euks: made of microtubules.

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14
Q

Bacteria do not undergo mitosis or meiosis, instead they undergo what?
Explain the process.

How do Euks divide?

A

Binary Fission.

  • 2 DNA Pols begin at ORI on circle and move in opposite directions, making complementary DNA double stranded circles
  • the cell then divides resulting in 2 genetically identical daughter cells
  • exponential growth

Euks: mitosis

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15
Q

What are transposons?

A

Pieces of DNA that can jump from one place to another along genome using transposase to be removed and added

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16
Q

Nucleus

***

A
  • like the brain
    • compartmentalization and storage of genetic info other than in mitochondria
  • aqueous fluid inside called Nucleoplasm
  • wrapped in Nuclear Envelope= double phospholipid bilayer which has Nuclear Pores
    * DNA cannot leave nucleus, RNA can!
    • Nucleolus: center of nucleus where rRNA is transcribed and the subunits of the ribosomes are assembled
17
Q

What happens to a newly synthesized protein?

**

A

Depending on the protein’s final destination:
- translated on ribosome in cytosol and stay there (eg, enzymes of glycolysis, actin filaments in muscle)
OR
- from ribosome on outer surface of ER, feed into lumen of Endoplasmic Reticulum (ER) (eg, protein hormones like ACTH; bloodstream proteins like Albumin)

18
Q

Describe the Rough Endoplasmic Reticulum (ER)

**

A
  • a thick maze of membranous walls with some places where the ER lumen is contiguous with the outer layer of the nuclear envelope
  • synthesizes all proteins that do not belong in the cytosol!
  • has ribosomes on the cytosolic side where mRNA is translated
  • signal sequence may be present on mRNA which directs the protein to the ER membrane for the completion of translation, and are propelled into the ER lumen as they are created
  • *= movement of protein from cytosol to ER
19
Q

What is the Golgi Apparatus?
What is the process whereby newly synthesized proteins from the ER lumen go to it?
**

A
  • series of flattened membrane bound sacs whose major functions are PACKAGING and SECRETING proteins
  • Transport Vesicles bud off from the ER and carry them across cytosol to cis face of Golgi.
20
Q

What does the Golgi do with the vesicles it receives?
(Trafficking of Secretory Proteins)
**

A
  • organizes, concentrates and modifies the proteins as they are shuttled by transport vesicles like an assembly line from one compartment to the next
  • ex, glycosylation, removal of AAs
  • then the vesicles are expelled by the trans face of Golgi as secretory vesicles… the cell will release the proteins [SECRETORY]
    OR
  • then the vesicles will be released from Golgi to mature into lysosomes
    OR
  • they’ll be transported to other parts of cell (ex, mitochondria or back to ER)
21
Q

Transport and Fate of Lysosomal Proteins

***

A

ER lumen –> cis-Golgi –> trans-Golgi –> lysosome

  • lysosomes= membrane-bound vesicles containing hydrolytic enzymes which breakdown macromolecules (taken into the cell by endocytosis) via hydrolysis ideally in acidic conditions
  • they’ll use these to breakdown old or damaged organelles; or digest the incoming phagocytes
  • if they rupture, they kill the cell
  • they exist mostly in cells that are about to undergo apoptosis
22
Q

Trafficking of Secretory Proteins
How does this process actually aid the cell
***

A

ER lumen –> cis-Golgi –> trans-Golgi –>secretory vesicle

  • secretory vesicles contain enzymes, growth factors or ECM components
  • released through exocytosis (where the vesicle membrane is incorporated into the cell membrane) – so they supply the membrane with its integral proteins and lipids + membrane expansion
  • secretory vesicles are constitutively secreted (released continuously) OR they’ll be released in response to chemical or electrical stimuli (regulated secretion)
  • some proteins are activated within secretory vesicles (ex, Proinsulin cleaves to Insulin only after the vesicle buds off the Golgi)

** Endocrine Glands (ex, pituitary and pancreas) and the Liver use this secretion path! (like you’ll see that the cells in these organs have ER and Golgi and do this)

23
Q

How does Endocytosis aid the cell?

**

A

The newly formed vesicles (which have just taken some cell membrane) enter and go to Golgi for recycling of the membrane. So when secretory vesicles are made again, the cell membrane gets a fresh batch.

24
Q

When you see smooth ER, what should you think about?

***

A

Lipid Metabolism and Storage; and Detoxification.
= portion of ER that lacks ribosomes
- (in smooth muscles, it’s called the Sarcoplasmic Reticulum)
Lipid Metabolism: in liver, triglycerides are made here and these lipids are stored as Adipocyte cells (contribute to energy storage and body temp) here.
Detoxification: it oxidizes foreign substances

25
Q

What are peroxisomes?

***

A

• organelles/vesicles in cytosol that collect peroxides

  • self-replicate
  • involved in the breakdown of hydrogen peroxide
  • inactivate toxic substances, regulate O2 concentration, etc.
26
Q

Mitochondria

***

A

• Site of ATP production
- according to the endosymbiotic theory, they evolved from a symbiotic relationship btwn ancient proks and euks
- so like proks, they contain circular DNA that replicates independently from nuclear DNA
• genes in mitochondrial DNA code for distinct mitochondrial RNA —> they have their own ribosomes!! —> can Self-replicate

  • but most proteins used for the self-replication process are coded for by nuclear DNA… Prime target for antibiotics that block translation of prokaryotic ribosomes, because it’ll block mitochondrial ribosomes –translation as well
  • mitochondrial DNA passed on from mother
27
Q

Inner and outer membrane structure of Mitochondria

**

A
  • like gram negative bacteria: mitochondria are surrounded by 2 phospholipid bilayers
  • inner membrane: invaginates (folds inward) to form cristae. Where ETC of aerobic respiration occurs
  • intermembrane space
  • outer membrane:
28
Q

Cytoskeleton general function in cell support and movement

**

A
  • anchors membrane proteins and other cellular components
  • moves compounds within the cell
  • moves cell
29
Q

Microfilaments: composition and role in cleavage and contractility
***

A
  • aka, actin filaments
  • smallest cytoskeleton group
  • protein subunit: actin monomer
    Reshapes the cell membrane:
  • interact with Myosin to cause skeletal muscle contraction in the sarcomere: they don’t change shape, but the myosin’s conformational change makes it pull the actin filaments (and thus, the Z disks) closer together which is contraction
    - same sort of thing in smooth muscles, just slower and longer
  • pinch the cytoplasm during cytokinesis (cleavage) via sarcomere-like organization creating a cleavage furrow in contractile ring
30
Q

Microtubules: composition and role in support and transport

A
  • made from globular protein alpha beta-Tubulin dimers. 13 long straight protofilaments of Tubulin come together to form the slanted microtubule
  • a singlet MT is unstable/dynamic (cytoplasm); doublets and triplets are stable (axonemal)
  • have a + (beta tubulin – binds GTP and GDP for hydrolysis) and - end (alpha)
  • can taxi things like secretory vesicles throughout the cell, or the chromosomes for mitosis
31
Q

What are Microtubule-Organizing Centers (MTOC)?
What is the major MTOC in animal cells?
How are MTs related to these?

A
  • required in order for MTs to be assembled. - end of MT attach to MTOC (exception: dendrites which have a mixed orientation of MTs) and it grows away from it at its + end.
  • major MTOC: Centrosome– composed of pair of Centrioles 90 degrees from each other, which function in the production of flagella and cilia but are not necessary for MT production. The centrioles are surrounded in pericentriolar material/matrix, and has MTs embedded within this matrix (but not touching the centrioles)
32
Q

What is the composition of Centrioles?

A

Made up of 9 triplets bound together to make a barrel/centriole

33
Q

Composition and function of cilia and flagella

A
  • specialized structures made from MTs
  • function: move fluid, causing the cell or nearby substances to move
  • composition: 9 MT doublets + 2 singlets – the doublets are connected by cross bridges made from Dynein which help the MTs to slide along their neighbours creating a whip action in cilia (moves the fluid laterally) or a wiggle action in flagella (moves fluid directly away from the cell up and down directions)
34
Q

Why might it be useful for a cell to be able to shift the fluid around it, other than for movement?

A
  • ex, in the respiratory tract, cilia move fluid and foreign substances so that they can be removed from the body
35
Q

Intermediate filaments, role in support

A
  • maintain cell shape/rigidity

- ex, Keratin

MCAT - Systems (Biology) (1 decks)

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