A2 Flashcards
Homeostasis
maintaining of a consistent internal environment even if the external environment changes
primordial soup
(hypothetical) water-based sea of simple monomers such as amino acids. This is thought to be the origin of living compounds
Vesicle
Any small bubble of fluid surrounded by a phospholipid bilayer
Compartmentalisation
Separation of functions into specific regions of the cells, allowing multiple distinct metabolic functions to occur at the same time
Coalescence
Phospholipids naturally arranging themselves to come together and form a ring-like structure
Three principles of cell theory
- All organisms are composed of one or more cells
- Cells are the smallest unit of life
- All cells come from pre-existing cells
Organic vs inorganic compound
Organic: generally complex carbon based compound, made in living organisms
Inorganic: don’t have to contain carbon (most don’t), found inside and outside living organisms
What did the Miller-Urey experiment demonstrate?
Inorganic gases can react to create organic compounds within conditions similar to early Earth.
How does the structure of fatty acids contribute to vesicle formation?
Phospholipids in an aqueous solution form a barrier to create a vesicle. This may have happened in primordial soup and creates cell membranes of early cells.
Requirements to be considered living
metabolism
growth
reproduction (independent)
response to stimuli
homeostasis
movement
nutrition
What is a cell?
Smallest unit of life
What is needed to create a living functional cell?
Catalysis: a catalyst that speeds up chemical reactions
Self-replication of molecules
Self-assembly of monomers into polymers (e.g. condensation reactions)
Compartmentalisation
- eukaryotes: organelles
- prokaryotes: ribosomes
Examples of how cells fulfill criteria for being living
Homeostasis -> regulates H2O balance
Metabolism (ability to carry out chemical reactions using ATP) -> cellular respiration happens in each cell
Reproduction/self-replication -> cell replication/mitosis
Examples of how viruses fail to meet the criteria for living
Homeostasis -/> no internal environment
Metabolism -/> does not use ATP
Reproduction/self-replication -/> needs a host
Conditions of the Miller Urey experiment
Inorganic gases: methane, ammonia, hydrogen
Vert hot ocean with water (due to high temperatures and lots of UV penetration)
Electrical activity (through an electrode)
= mimics conditions of Early Earth
Process of Miller Urey experiment
A lower chamber (the ocean) is heated, to mimic the hihg temperatures of Early Earth.
This produces water vapour that travels into the upper chamber. This upper chamber is filled with inorganic gases (methane, ammonia, hydrogen), which mixes with the H2O vapour. An electrode hits this upper chamber, to mimic lightning.
This goes through a condenser.
Proucts of the Miller Urey experiment.
Amino acids + carbon hydrogen chains, as well as water vapour. This combination is dubbed primordial soup. This contributed to evidence that biomolecules could spontaneously form under Early Earth’s conditions.
What does spontaneous vesicle formation provide evidence for?
Explains how all membranes arrived.
What is the process of spontaneous vesicle formation?
Amphipathic phospholipids spontaneously form a vesicle due to hydrophobic interactions
Ribozymes
Special type of RNA that can act as a catalyst. Has a role in protein synthesis
Protocell
General term for any unit contained by a membrane that is completing a cellular reaction
Radioactive isotope
Unstable form of an element that emits radiation
Half life
Length of time it takes for half of a radioactive isotope to change into another stable element
Index fossils
Distinctive, widespread and abundant fossils that is limited to a specific geological time
Hydrothermal vents
Places where hot water emanates from beneath the ocena floor. Formed when cracks of the crust of the seabed expose seawater to rocks below
Unique properties of RNA that suggest it could be an ideal first genetic material
Can spontaneously form from monomers as it is a simpler structure than DNA
Self-replicating properties
Can catalyse chemical reactions
Sequence of major stages in the evolution of life
Abiotic chemical compounds e.g. methane
Small organic compounds e.g. primordial soup
Polymers (aids by RNA catalysis)
Membranes (due to amphipathic nature)
Protocell
True cell with organelles
Last Universal Common Ancestor
Common ancestor to all currently living things. i.e. from before all prokaryotes and eukaryotes branched off
Relative dating of fossils
Whether the fossil is comparatively older or younger than nearby fossils absed on their placement in the rock
Absolute dating of fossils
Determining a specific age of a fossil in years, using carbon dating and knowledge of half lives
What is the RNA World Hypothesis?
Evolutionary theory that RNA was the initial genetic material, and evolved into DNA and proteins. This is contrasted by the Central dogma, which states DNA -> RNA -> proteins
Specific hypothesised details of RNA World Hypothesis
Within primordial soup, RNA easily self assembled. This is because of its simple structure. The RNA can then act as a catalyst for DNA replication (which requires many enzymes) and protein synthesis (ribozymes in RNA still do this).
Evidence for shared ancestry/Last Universal Common Ancestor
Universal genetic code
Same biomolecules
Same metabolic processes
Tracked ~300 shared genes
Why is it hypothesised that LUCA is in hydrothermal vents?
The ~300 shared genes were for anaerobic processes (occuring in the absence of O2). Therefore, LUCA may be found in a low oxygen environment. This low O2 environment, and other favourable conditions and many fossils, fits with Hydrothermal Vents
Most common substance for absolute dating of fossils
Carbon-14
5730 years half life
Cytology
Specific branch of biology focused on the study of the cell and all aspects related to cellular structure and function
Micrograph
Photo taken through a microscope
Micrometre compared to one centimetre
1 micrometre = 10^-4 cm = 10^-3 mm
Coarse v.s. fine focus on a microscope
Coarse makes larger adjustments to bring objects into focus
Fine makes small adjustments to add sharpness and clarity.
Contribution of cryogenic electron microscopy
Provides a resolution at 0.12 nanometres, allowing for the atoms within a protein to be visualised
Magnification
How many times larger the viewed image is than the actual image size
Resolution
How well you can differentiate two objects as separate (i.e. clarity and sharpness)
With a light microscope, what occurs when magnification increases?
Resolution decreases. Therefore, ideal magnification of a light microscope is 400-1000x, although some light microscopes can reach 2000x
What is the difference between electron and light microscopes in terms of resolution/magnification?
Electron microscopes can preserve resolution even at high magnifications. However, light microscopes decrease in resolution as magnification increases, usually working from 400-1000x
Formula for magnification
Magnification = image size/actual size
How to calculate magnification using a scale bar
Magnification = measured scale bar with ruler / given size on bar
What can light microscopes observe?
Living organisms. Both surface and internal (if thin).
Creates 2D images
What magnification do light microscopes work well with?
400-1000x. Some can go up to 2000x
What type of images do light microscopes create?
2D
Advantages of light microscopes
Can observe living organisms (see processes in action)
Can be in colour
Affordable (increases access)
Disadvantages of light microscopes
Poor resolution limits magnification
What is a scanning electron microscope (SEM)?
Electron microscope that uses a beam of electrons to scan outer surfaces of dead matter, creating detailed images of the exterior
What is a transmission electron microscope (TEM)?
Electron microscope that uses a beam of electrons through a very thin section of specimen that allows for internal structures to be viewed.
What can scanning electron microscopes observe?
Dead matter, detailed 3D images of surface.
Magnification of scanning electron microscopes
Up to 1,000,000x with great resolution
Advantages of scanning electron microscope
Higher magnification, 3D images
Disadvantages of scanning electron microscopes
Only black and white
Only non-living matter
Expensive
Type of images created by scanning electron microscopes
3D
What can transmission electron microscopes observe?
Dead matter, 2D images of internal structures
Magnification of transmission electron microscopes
Up to 1,000,000x with great resolution
Advantages of transmission electron microscopes
Higher magnification, has revealed organelle structure
Disadvantages of transmission electron microscopes
Must be very thin specimen (techniques required)
Non-living
Black and white only
Expensive
Advances to micrography
Freeze fracturing
Cryogenic electron microscopy
Use of fluorescent stain
Freeze fracturing
Technique that aids in viewing internal structures with an electron microscope.
Specimen is frozen and then broken at plane (i.e. fracture plane). Then, an etching of the plane is created and observed under an electron microscope
What scientific developments are a result of freeze fracturing?
Understanding the bilayer
Cryogenic electron microscopy
Protein structure is frozen on grid. The grid is placed under an electron microscope. Pattern of electron transmission reveals the structure of protein down to atoms. Software is used ot create a 3D image
What scientific developments are a result of cryogenic electron microscopy?
Detailed understanding of protein structure
Fluroescent stain
Fluroescent stain binds to a cellular component (only binds with specific ones). This is observed with a fluroescent light via microscopes with UV lights.
What scientific developments are a result of fluroescent stain?
Bright images of cellular structures
Immunofluoresence
Technique that uses antibodies with flurosence added. Antibodies are matched to bind to certain target molecules and give them a viral glow once bound
What scientific developments are a result of immunoflourescence?
Visualisation of specific proteins (i.e. whether present or not)
Prokaryotic cell
Simple and small cells that lack complex organelles
Eukaryotic cell
More complex cells that have membrane-bound organelles carrying out unique functions & all DNA is enclosed in a nucleus
Peptidoglycan
Carbohydrate and protein polymer that usually makes up the cell wall of prokaryotes
Features common to all cells
Cell membrane
DNA
Ribosomes
Cytoplasm
Gram positive bacteria
Has thick layer of peptidoglycan as cell wall
Gram negative bacteria
Has additional thin layer of membrane surrounding the thick layer of peptidoglycan
Examples of eukaryotic organelles
Nucleus
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
Golgi apparatus
Mitochondria
Difference between ribosomes of prokaryotes and eukaryotes
In eukaryotes, ribosomes are 80s and are larger and denser than the 70s ribosomes of prokaryotes.
Similarities between ribosomes of prokaryotes and eukaryotes
Both are made of two separate subunits that clamp together in translation
Functions that a unicellular organism must carry out to be classified as living
Metabolism
growth
reproduction
reponse to stimuli
homeostasis
nutrition
excretion
movement
Size difference between prokaryotes and eukaryotes
Eukaryotes are much larger
Features of all prokaryotic cells
Cell membrane
cell wall
DNA/nucleoid region
ribosomes
cytoplasm
Features of some prokaryotic cells
Plasmids
Flagellum
Capsule
Pili
Cytoplasms
Interior of the cell, containing the fluid cytosol. Provides internal space for chemical reactions (metabolic processes). Other cellular structures can exist within them
Ribosomes
Sites of translation where polypeptides are formed. No exterior membrane and made up of mRNA/protein
Pili
Small hair structures on the outside of a cell wall. Can be used for adhesion/attachment to other prokaryotic cells or to
facilitate DNA exchange (as a part of sexual reproduction)
Nucleoid region (prokaryotic cell)
One circular region where the DNA of a prokaryotic cell is found.
This DNA is free in the cytoplasm with no nucleus, providing instructions
Cell wall
Rigid external layer that is specifically designed to provide structural support and rigidity
Different cell wall materials across cell types
Bacteria (almost all have) = peptidoglycan
Plant = cellulose
Fungi (many have) = chitin
Do all prokaryotes have a cell wall?
Almost all esp. bacteria
Cell membrane
Phospholipid bilayer that allows transport in + out of the cell.
Therefore, it has a role in homeostasis, transport and cell communication
What organelle has a role in homeostasis?
Most important is the cell membrane
Capsule
Additional thick layer outside the cell wall, made up of polysaccharides.
Allows adhesion + protection
Some bacteria have
Do all prokaryotic cells have a capsule?
No, just some bacteria
Flagellum
Whip-like tail for movement/locomotion
Plasmids
Single circular rings of DNA that are not connected to the main chromosome. Not essential but helpful. Often contain additional adaptive DNA e.g. antibiotic resistance
Organelles specific to animal cells
Centrosomes and lysosomes
Organelles specific to plant cells (not animal cells)
Chloroplasts
Cell wall
Large central vacuole
Amyloplast
Organelles of animal cells
Golgi apparatus
Rough endoplasmic reticulum
Ribosomes
Plasma membrane
Nucleus
Smooth endoplasmic reticulum
Lysosomes
Centrosome
Cytoskeleton
Small vacuole
Cytoplasm
Mitochondria
Rough endoplasmic reticulum
Interconnected network of tubules extending from the nucleus throughout the cell with ribosomes on the surface. Transports polypeptides in cell
Two types of eukaryotic ribosome
Free or attached
Nucleus
Organelle in which DNA resides. Has a porous double membrane (nuclear envelope) that mRNA exits from.
Contains linear DNA wrapped around histones.
Contains a spherical structure that produces and assembles ribosomal subunits -> nucleolus
Smooth endoplasmic reticulum
Interconnected network of tubules that extend from the nucleus without ribosomes. Makes and transports lipids e.g. phospholipids, steroids
Lysosome
Single membrane vesicle full of hydrolytic enzymes to break down biomolecules
What type of cells are cytoskeletons found in?
All eukaryotic cells
Cytoskeleton
Network of filaments and microtubules that maintain cell shape, anchor organelles, aid in cell and organelle movement, etc.
Small vacuole
(Found in animal cells) Storage organelle formed by the Golgi Apparatus that stores H2O, food, wastes, etc.
Mitochondria
Rod-shaped organelle that performs aerobic cellular respiration.
Has its own DNA and ribosomes, as well as highly folded innner membrane
Centrosome (two centrioles)
Structure of animal cell that aids in cell division
Golgi apparatus
Set of flattened saccs (cisternae) that collect/packages/modifies/distributes cellular products
Organelles of plant cell
Chloroplast
Golgi apparatus
Rough ER
RIbosomes
Cell membrane
Mitochondria
Cell wall
Smooth ER
Nucleus
large central vacuole
Purpose of cell wall in plants
Protection and structure of cell
Purpose of large central vacuole
Storage organelle that stores water and other materials.
What happens if the large central vacuole is full in plant cells?
Gives turgidity/shape to the cell
Plant organelle that not all have
Amyloplast
Amyloplast
Plant organelle (not all have) that stores starch granules inside cell
Chloroplast
Organelle that has flattened membrane discs (thylakoids) to absorb sunlight for photosynthesis to make glucose.
Has inner and outermembrane, as well as own DNA and ribosomes
Specialised cells
Cells that change structure to carry out a specific function within a multicellular organism
Cell differentiation
Process by which a stem cell turns off unneeded genes and expresses only ones relevant to its function in order to become specialised
Characteristics of animal cells that make them unique from other eukaryotes
No cell wall, centrioles that form the centrosome, store carbohydrates in specialised cells, small and numerous vacuoles, may have flagella
Characteristics of plant cells that make them unique from other eukaryotes
Fixed cell wall shape, chloroplasts for photosynthesis, large central vacuole for storage, no flagella/cili, no centrioles
Characteristics of funal cells that make them unique from other eukaryotes
Protective and flexible cell wall, no chloroplasts, store carfbohydrates, no centrioles, occasionally have cilia
What allows for cells to differentiate in multicellular organisms?
Only some genes are expressed/used
Do animal cells have plastids?
No
Do animal cells have a cell wall?
No, which makes them flexible and round
Do animal cells have vacuoles?
Yes. Small and many - can have different functions
DO animal cells have centrioles?
Yes. They grow microtubules for mitosis
Cilia
Small, hair-like structures present on the surface of some animal cells. Used for trapped dust, pathogens and food
Do animal cells have cilia?
Lots do
Do animal cells have flagella?
Some have a flagella
Do plant cells have plastids?
Yes (chloroplasts and amyloplasts)
Do plant cells have a cell wall?
Yes, made of cellulose, which creates a fixed and angular shape
Do plant cells have vacuoles?
Yes, one large central vacuoles that stores all components
Do plant cells have centrioles?
No. They do have a centrosome region that grows microtubules
Do plant cells have cilia/flagella?
Rarely have either, as they make their own food source
Do fungal cells have plastids
No
Do fungal cells have a cell wall?
Yes made of chitin, which makes the fungal cells protective anf flexible
Do fungal cells have vacuoles?
Depends on fungal species, but either like animal (small and many) or plant (one central)
Do fungal cells have centrioles?
No, but they do have a centrosome region that grows microtubules
Do fungal cells have cilia/pili?
Rarely have either
Examples of atypical cells that break the ‘one nucleus per cell’ rule
Fungal hyphae
Phloem sieve tube element
Skeletal muscle cells
Red blood cells
SIgn that a cell is specialised
Lack certain crucial organelles
Fungal hyphae (atypical cell example)
Long one-cell-wide filaments with many nuclei, due to a loss of membrane between cells.
Produced by fungi, usually expand underground and play a role in cell absorption
Phloem sieve tube elements (atypical cell example)
Cells that form thin tubes to transport sugars in plants.
Lost all organelles, so have companion cells with a nucleus and mitochondria. These companion cells meet the needs of the sieve cells as well as their own
Skeletal muscle cells (atypical cell example)
Long tubular cells that can contract and relax with multiple nuclei. Have internal and external mitochondria / additional mitochondria
Fibres of long thin cells = best for contractions
How are skeletal muscle cells adapted for contraction?
Fibres of long thin cells = best for contractions
Red blood cells (atypical cell example)
No nucleus in order to reduce volume and thus, increase SA:V to allow more haemoglobin to be at the surface to carry more O2.
This is also seen with the biconcave shape
Are red blood cells considered to be cells?
No, as they lack the criteria
Endosymbiotic theory
Theory that an early eukaryotic ancestor engulfed a prokaryotic cell, which remained functional due to no enzymes to digest. The prokaryote functions inside the eukaryote, producing energy for the eukaryote to use. This makes this particular eukaryote the fittest of all cells. Overtime, due to natural selection, eukaryotes with this adaptation became the norm. The prokaryote became mitochondria first, and then later some cells gained a chlorplast through a similar process
Evidence for endosymbiotic theory
Both mitochondria and chloroplasts have:
Own 70s (prokaryote size) ribosomes -> not from parent cell
Double membrane -> outer one from host (gained when entering cell)
Own DNA. Circular like that of prokaryotes
Same size as prokaryotes
Self-replicate separate to cell
i.e. behave like a prokaryote
How do multicellular organisms develop specialised cells?
Gene expression (i.e. turning genes on)
Virus
Non-living particle that infects cells and reproduces inside of them
Capsid
Simple protein that contains the genetic material of a virus.
Prophage
The combined nucleic acid of the viral DNA and host DNA
Outbreak v.s. epidemic v.s. pandemic
Outbreak = spread of infection isolated to a small geographic area
Epidemic = moves more quickly than expected and to more areas
Pandemic: epidemic crosses countries
In what forms can genetic material of viruses exist?
DNA
RNA
RNA transcribed to mRNA
RNA reversed transcribed to DNA
Features common to all viruses
Protein spikes
Nucleic acid
Protein capsid
Are viruses living?
No
Role of protein spikes in viruses
These protein spikes are a form of ID recognised by the host, allowing the virus to invade the host cell
What is a common feature of viruses (many not all)?
An envelope that surrounds the protein capsid. This envelope is a phospholipid bilayer and is the host cell’s membrane
Types of nucleic acid within viruses
DNA: either double or single stranded
RNA: either double or singl estranded
Host cell of bacteriophage lambda
E. Coli bacteria
Nucleic acid of bacteriophage lambda
Double stranded DNA
Structure of bacteriophage lambda
Has capsid and DNA, tail sheath, base plate with protein spikes and tail fibres
Life cycle of bacteriophage lambda
Can follow either lytic or lysogenic life cycle
Host cells of Coronavirus
Human respiratory cells
Nucleic acid of coronavirus
Single stranded RNA
Structure of coronavirus
Spherical shape, single stranded RNA as genetic material, envelope and capsid attached closely to RNA, spike proteins on the envelope.
What is Coronavirus an example of?
Zoonosis (transferred between species)
Host cell of Human Immunodeficiency Virus (HIV)
Human Helper T Cells (WBCs)
Nucleic acid of Human Immunodeficiency Virus
Two identical RNA strands that convert into DNAS
Structure of HIV
Two identical strands of RNA (that are copied into DNA) and the reverse transcripase enzyme within a capsid coat; outer envelope; glycoprotein spikes
Extra information about Human Immunodeficiency Virus
Is a retrovirus. If untreated, causes AIDS (acquired immunodeficiency syndrome)
Lytic cycle steps
Step one: attachment (virus attaches to host cell)
Step two: DNA penetration (virus inserts DNA into host cell)
Step three: DNA replication
Step four: transcription (DNA is transcribed to become mRNA)
Step five: translation of viral parts
Step six: assembly and lysis (viral parts assemble into viruses, placing pressure on the cell, which forces it to lyse and release virus)
How quickly will symptoms occur if a virus works in the lytic cycle?
Quickly
How is the lysogenic crycle different to the lytic cycle?
Involves integration of viral DNA into the host DNA without being used to make viral parts. Slowly spreads as the cell reproduces. If viral DNA is released from the prophage, the lytic cycle is initiated
Steps of lysogenic life cycle
Step one: attachment (virus attaches to host cell)
Step two: DNA penetration (virus releases DNA into the host cell)
Step three: integration (viral DNA combines with the hsot DNA to become a prophage)
Step four: cell division (mitosis or binary fission)
Could leave the prophage and enter the lytic cycle
Step five: DNA replication
Step six: transcription
Step seven: translation of viral parts
Step eight: assembly and lysis
Why might viruses be an example of convergent evolution?
Wide variety in viral structure so are likely to have evolved separately and lack a common ancestor. This is seen through the diversity in genetic material
All similarities are a result of convergent evolution (e.g. spikes for attachment)
Theories about where viruses come from
Viruses first hypothesis
Regressive hypothesis
Progress hypothesis
Virus first hypothesis
Viruses existed before cells. Cells evolved from them
Why is the virus first hypothesis weak?
Viruses have genetic diversity + primordial soup was the origin of cells
Regressive hypothesis
Viruses were once cells that lost structure and function, becoming reliant on a host
Progressive hypothesis
Cellular components escaped, evolving into a virus by gaining function
Antigenic shift
Two or more different viruses invade the same cell and recombine genetic material, leading to dramatic changes in a short amount of time.
Example of antigenic shift
Influenza
What is the result of antigenic shift?
Rapid new virus formation, with new spikes that are not recognised by memory cells
Antigenic Drift
Once a virus invades a host, mutations occur to the viral DNA within a host cell. These smaller genetic changes accumulate overtime, leading to a new virus that is no longer recognised.
Example of antigenic drift
HIV
Why did the influenza virus evolve so rapidly?
Antigenic shift
What contributes to the rapid evolution rate of HIV?
Antigenic drift
