Cells - Fundamental Unit Flashcards
In what ways can cells differ?
- Size (e.g. bacterial cell X frog egg), shape (e.g. neuron X paramecium), chemical requirements (e.g. require O2 X needs more molecules X O2 is toxic), function (e.g. creating hormones X mechanical work of muscles), level of specialization (e.g. one cell X multicellular organism)
Since defining life can be difficult - what kind of characteristics do we usually look for?
- Highly organized structures (x inanimate objects)
- Homeostasis
- Reproduction
- Start simple -> grow and develop further
- Take energy and matter from the environment and transform it
- Respond to stimuli
- Capacity to adapt to environment
Despite infinite variaty of cells - on bichemical level they share the same: molecules, chemical reactions -> what in this case is Central Dogma?
Central dogma refers to the fundamental information exchange that happens within cells. Specifically: DNA made up of chain of 4 monomers called nucleotides -> information gets TRANSCRIBED into polymer (combination of monomers) called RNA -> subset of RNA molecules is TRANSLATED into polymer called PROTEIN.
What can be said about proteins?
- Dictate the behavior of cells
- Build up from amino acids
- All organisms use the same 20 aminoacids linked in different sequence => giving them a different 3-dimensional shape = conformation
Why can’t viruses reproduce by themselves?
Because they don’t have the energy and molecular machinery required for replication
What is the biochemical principle of evolution (sexual and non-sexual reproduction)?
During reproduction DNA has to be copied and cell divided -> BUT sometimes mutations occur in the daughter cells that could change the offsprings to:
- worse (eliminated)
- better (favoured)
- neutral i.e. mutation present but still viable (tolarated)
Plus sexual reproduction (e.i. combination of different cells) also deals with shuffling of genetic cards
NOTE: all cells likely have the same ancestor that gave basis to the cellular mechanisms
How come we can get such variety in cells e.g. neuron X osteocytes?
Although all cells of the organism share the same whole DNA sequence (= cell’s GENOME) they are capable of choosing genetic instructions relevant to them and “ignoring” the others depending on certain cues e.g. signaling molecules in the surrounding
What was meant by spontaneous generation and cell theory? How was cell theory supported?
Spontaneous generation proposed that life can arose from nothing while cell theory argued that living cells are formed only via growth and division of existing cells
Pasteur: He used a closed flask and brought the water inside to boil (to get O2):
-> one flask never opened
-> one that was opened
=> only the opened one produced cells i.e. contamination was needed, life doesn’t grow from nothing
How could we see cells and their components?
- Stain cells with dyes that color a particular components (=organelles) differently
- e.g. fluorescence microscope (now could make even single ribosome visible) - Use the fact that components have different reflecitve indexes
- The best technique now = electrone microscope
- can even make plasma membranes, and internal membranes (of organelles) visible
What does the division into eukaryotes and prokaryotes mean?
Eukaryotes are organisms WITH nucleus that encases their DNA (Greek “eu” = “well/trully”, “karyon” = “nucleus”)
- usually bigger, more elaborate (although can also live alone e.g. yeast)
Prokaryotes do NOT have nucleus (Greek “pro” = “before”)
- no organelles, just cytoplasma and DNA
- rapid division and growth -> better ability to resist being killed by antibiotic
What can you remember about prokaryotes? What kind of organelles are connected to bacteria and how?
- some live alone X some join i chains, clusters
- expanded to all kinds of habitats e.g. puddle X human body
- may satisfy their needs in various ways
- living on organic or inorganic substances
- Some organelles are thought to have developed from bacteria that was living inside ancestor of current cells e.g. mitochondria, chloroplasts
- NOTE: at this point the cooperation is so intertwind that they wouldn’t survive without their “host” cell
- NOTE: the two became one organism due to a symbiotic relationship they established before living inside the cell
What 2 classes do we encounter in prokaryotic cells?
- Bacteria and Archae
- on a molecular level completely different, archae can survive even more severe conditions than bacteria e.g. volcano
What is the function of nucleus in eukaryotic cells?
- enclosed in 2 concentric membrane that form NUCLEAR ENVELOPE (kept separate from the rest of the organelles)
- contains DNA - genetic information
What is the function and structure of mitochondria in eukaryotic cells?
- have 2 membranes: inner (extends and folds inside), outer
- harness energy from oxydation of food molecules e.g. sugars -> turns into adenosine triphospate (ATP)
- since it uses O2 and in process also produces CO2 we call it CELLULAR RESPIRATION
- since they have their own DNA they can reproduce by division
What is the function and structure of chloroplasts in eukaryotic cells?
- 2 surrounding membranes
- Internal stacks of membranes containing chlorophyll
- Photosynthesis - capture sun-light energy and use it for manifacturing sugar molecules
- release oxygen as by-product
- further can use these products in mitochondria to get ATP
- Have their own DNA, division
What other intracellular compartments can you think of and what are their functions?
- Endoplasmatic reticulum (ER) - complex of interconnected membranes which makes most of cell-membrane components and materials that will be later exported
- Golgi apparatus - modifies and packages molecules made in ER (that are mean to be later secreted or transported somewhere)
- Lysosomes - intercellular nutrient digestion, breaking down unwanted molecules (to be recycled or later released from the cell)
- Peroxisomes - enclosed vesicles in which hydrogen peroxide is used to inactivate toxic molecules
- Transport vesicles - allow exchange of molecules between organelles and outside of the cell
- done via endo- (towards inside) and exocytosis (going outside)
Which of these structures are present in both eukaryotes and prokaryotes: ribosomes, cytosol, mitochondria, chloroplasts, plasma membrane, endoplasmatic reticulum, nucleus
Answer: ribosomes, cytosol, plasma membrane
What is the largest cell compartment? What is its function?
Cytosol = a gel-like part of cytoplasm that is not contained within intracellular membranes
- includes densily crowded molecules -> provides space for the most fundamental chemical reactions e.g. breakdown of nutrients
How come the gelatenous cytoplasm doesn’t colapse on itself? Three types - function?
Cytoskeleton = criss-cross fine filament structure
- Actin filaments = thinnest, large numbers in muscle cells -> serve role in muscle contractions
- Intermediate filaments = strenghtening the cell
- Microtubules = thickest, in a dividing cell pull duplicated chromosomes apart and distribute them equally to daughter cells
=> all together give cell its shape, guides movement, equality in division
Is cytoplasm more static or dynamic - explain your answer.
Dynamic - there is constant reorganization of the filaments (can assemble and disappear within minutes), motor proteins move along filaments carrying organelles, molecules swept back and forth by thermal motion
What is the theory of eukaryotic cell development?
The predecessor of eukaryotic cell was likely a predator -> requires larger size, flexible membrane and cytoskeleton that can hold the cell despite its movement
- possibly why DNA is in nucleus - to segregate it from all the other physical and chemical forces
- likely engulfted bacteria ancestor of mitochondria and chloroplasts
NOTE: example predators - protozoans (could e.g. shoot paralyzing darts and devour its prey)
Look over the structures in the picture:
Model Organisms: which one is relevant for molecular biologists? What have we found out?
Escherichia coli = E. coli
- normally in gut of humans and other vertebrates
- easy to reproduce in lab environment
=> most of the knowledge about DNA replication and decoding of genetic instructions for proteins
Model Organisms: what is usually used as a simple eukaryotic cell
Saccharomyces cerevisiae = S. cerevisiae
- so called Brewer’s yeast, fangus (used for brewing beer and baking bread)
- immobile, has mitochondria but no chloroplasts -> same tasks as an eukarytic cell (considered to be similar to both animals and plants)
=> Used to study eukaryotic cell division, discovery of cell-division cycle genes (Cdc genes)
