A2 Flashcards
Define primordial soup
A solution of simple monomers including amino acids, and hydrogen and carbon chains. It is thought that the origin of living compounds began in this water based solution in the sea.
Define homeostasis
The maintainence of a consistent internal environment despite a changing external environment. It is an essential requirement of living organisms to maintain some constants.
Define vesicles
Vesicles are any small bubble of fluid surrounded by a phospholipid bilayer. Vesicles form automatically when phosphilipids are in water- this could model how cells could originate. Vesicles can also form by established membranes breaking off.
Define compartmentalisation
The seperation of functions for specific regions of the cell (organelles), allowing multiple distinct metabolic functions to occur at the same time.
Define coalescence
Coalescence is vesicle/ membrane formation. The natural coming together of things. In this context it refers to fatty acids/ phospholipids arranging themselves away from water, thus coming together and forming a ring.
How were the abiotic conditions of early Earth different from current conditions?
The abiotic conditions of early Earth allowed for spontaneous formation of compounds that occur now.
* The gases present included methane, ammonia and hydrogen sulfide- there was very little oxygen.
* There was high penetration of UV light (no ozone layer) leading to high temperatures.
* There was regular lighting
What are the requirements for something to be considered living?
- Metabolism
- Growth
- Reproduction (without a host)
- Respond to their environment
- Maintain homeostasis
- Use food for energy
What are the 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
What are the requirements necessary for cells to evolve?
- Catalysis (enzymes to speed up chemical reactions)
- Self-replication of molecules needed
- Self- assembly of those molecules into large polymers and structures/ organelles
- Compartmentalisation- functions assigned to organelles
What is the difference between an inorganic and an organic compound?
Organic- a generally complex carbon (and hydrogen) based compound- made in living organisms and play a crucial role in living processes
Inorganic- do not have to contain carbon (most do not) and are often found outside of living organisms as well as inside them- often simpler than organic
Explain the Miller-Urey experiment
- Wanted to test the hypothesis that inorganic gases could react (in early earth conditions) to create organic compounds.
- Tested this by creating 2 chambers, one with boiling water and one with gases (methane, ammonia, hydrogen) and electrodes to represent lightning
- The water vapour would travel though a tube and combine with the inorganic gases
- Once condensed into liquid, they found an aqueous solution containing amino acids and carbon hydrogen chains (primordial soup)
- This is evidence that there could have been spontaneous/ natural formation of biomolecules/ monomers in early Earth conditions.
Describe spontaneous vesicle formation
Phospholipids in aqueous solution naturally form a barrier to create a vesicle. If fatty acids were present in primordial soup, then this process could have created early cell membranes.
Define ribozymes
A special type of RNA that can act as a catalyst in protein synthesis. There is evidence they were the first catalyst, before protein based enzymes.
Define protocell
The general term for any unit contained by a membrane that completes cellular action. Thought to be the origin of life. They are likely the ancestors of modern cells, before compartmentalisation and self-replication to become ‘true cells’
What is a radioactive isotope?
An unstable form of an element that emits radiation, this radiation can be measured. Radioactive isotopes are used to date fossils by comparing the original amount to the current amount as it degrades steadily.
Define half-life (of a radioactive isotope)
The length of time it takes for a half of a radioactive isotope to turn into another stable element. This is known for the element, and used to date fossils, most commonly with C-14.
What are index fossils?
Distinctive, widespread fossils that are abundant but limited to a certain geological time. These can be used to compareto other fossils using the location in the rock layers.
What are hydrothermal vents?
Places where hot water come from beneath the ocean floor. They form cracks in the seabed which exposes the water to magma heated rocks. They are extremely hot and have low oxygen, but some organisms still live there
What is the RNA world hypothesis?
For primordial soup to progress to polymers through self-assemly, a catalyst is needed. The RNA world hypothesis states that RNA could have been the catalyst, and pre-dated DNA
What is the evidence for the RNA world hypothesis?
RNA is:
* A simple, single stranded nucleic acid
* Can spontaneously form from monomers
* Easily assembled
* Can act as a catalyst- we know this because of ribozymes currently doing this
* Can be used to make proteins and DNA
* Has self-replicating properties
What does LUCA stand for?
Last Universal Common Ancestor
What is the sequence of the major stages of the evolution of life?
- Abiotic chemical compounds existed
- Led to the creation of small, organic compounds (primordial soup)
- Assembled into polymers (aided by RNA catalysis)
- Membranes spontaneously formed
- Protocells exist
- Compartmentalisation
- A true cell with organelles form
What is LUCA?
The last common ancestor to all currently living organisms
What is the evidence for shared ancestry (LUCA)
- Universal genetic code
- Same biomolecules and metabolic processes
- 300 genes were tracked that are shared between all living organisms- genes involved in anaerobic processes (absence of oxygen)
Where is LUCA found?
- Low oxygen environment
- Other favourable conditions
- HYDROTHERMAL VENTS
- How do we know this? old fossils were found there
What is relative fossil dating?
Relative fossil dating considers whether a fossil is older or younger than nearby fossils, based on the placement in rock in relation to an index fossil (lower is older)
What is absolute fossil dating?
Absolute fossil dating attempts to determine an age of the fossil in years. This relies on carbon dating using the half-life of radioisotopes of carbon
Define cytology
Cytology is a branch of biology focused on the study of the cell, including cell structure and function. It heavily relies on the use of microscopes.
Define magnification
The increase in an objects image size compared to its actual size. How many times larger the viewed image is than the actual image
How do you calculate magnification?
Magnification= measured scale bar with ruler/ given size on bar
Define resolution
The minimum distance between two points/ objects at which they can be distinguished as two seperate objects.
What is a micrograph?
The image taken through a microscope to show the view of the microscope (light or electron).
Describe the process of freeze fracturing
- Cell is frozen
- Cell is broken at a plane known as the fracture plane
- Create an etching of the plane
- Observe the etching under an electron microscope
What has freeze fracturing helped us understand?
Freeze fracturing is how we have come to understand the bilayer
Describe the process of cryogenic electron microscopy (cryo-EM)
- A protein solution is frozen on a grid (in ethanol)
- The grid is placed in an electron microscope
- The pattern of the electron transmission reveals the structure of the protein, down to the atoms
- The software creates a 3D image
Describe the process of using flurescent stains
- Flurescent stain is added to the cells
- The stain sticks to a cellular component
- These are observed with a flurescent light with a UV light microscope
What has cryo-EM helped us understand?
Allowed for detailed understanding of protein structure
What has flurescent stains helped us understand?
Helped us see bright images of cellular structure
Describe the process of immunoflurescence
- Antibodies to specific proteins are added- these antibodies have flurescence attached to them
- The presence of proteins can be determined by observing flurescence under a UV light microscope
What has immunoflurescence helped us understand?
It allows for visualisation of specific proteins (present or not)
What is the difference between a scanning electron microscope and a transmission electron microscope?
SEM: uses a beam of electron to scan outer surfacer of the specimen, gives a detailed 3D image of surface
TEM: beams electrons through a thin section of specimen, allows internal structures to be viewed
What are the benefits of light microscopes?
- Can observe living organisms and their processes
- Can view surface and some internal structures (2D only)
- Can be in colour- important for viewing pigments etc
- Affordable and accessable
What are the disadvantages of light microscopes?
- Poor resolution which limits magnification- can only magnify up to 2,000x (most 400x to 1,000x)
- This means they cannot view organelles
What are the advantages of electron microscopes?
- Higher magnification- up to 1,000,000x with strong resolution
- SEM: shows 3D external imagr
- TEM: can reveal organelle structure
What are the disadvantages of electron microscopes?
- Black and white images only
- Specimens have to be non-living
- Very expensive
- TEM: requires a thin plane of specimen
Define prokaryotic
Simple unicellular organisms, e.g bacteria. Small and simple, lacking complex organelles (no compartmentalisation)
Define eukaryotic
Larger, more compex cells that make up plants, animals, fungi and protists. All DNA is contained within a nucleus. Also contains membrane bound organelles with unique functions
What is peptidoglycan?
A carbohydrate and protein polymer that makes up prokaryotic bacteria cell walls. note: only bacteria, archae have a cell wall made of different polymers
What features are common to all cells?
- Cell membrane/ phospholipid bilayer
- DNA
- Ribosomes
- Cytoplasm
Explain the structure and function of a capsule (bacteria)
Some bacteria have an additional thick layer outside the cell wall. Made of polysaccharides.
Used for adhesion to other organisms structures e.g teeth, hair
Explain the structure and function of pili (bacteria)
Small hair structures outside the cell wall.
Can be used to attach onto other organisms. Also plays a role in the sexual reproduction of bacteria. Pili allow 2 bacteria cells to join and exchange DNA
Explain the structure and function of flagella (bacteria)
Some bacteria have flagellum or flagella. A whip like tail.
Used for movement. note: can also be present in eukaryotes
Explain the structure and function of plasmids (bacteria)
Plasmids are additional small rings of DNA not connected to the main chromosome. They are non-essential and replicate seperately.
They often contain helpful adaptive genes e.g antibiotic resistance.
Note: can be transferred between bacteria
What is the difference between gram positive and gram negative bacteria?
Gram positive: thick layer of peptidoglycan as its cell wall
Gram negative: has a thin layer of peptidoglycan underneath an additional outer membrane
Explain the structure and function of cytoplasm
The interior of prokaryotic and eukaryotic cells. Made of cytosol with other cellular structures inside.
In prokaryotes, it performs many chemical reactions.
In eukaryotes, it contains the cytoskeleton to maintain shape
Explain the structure and function of the nucleus
The region of eukaryotic cells where DNA resides. It has a double membrane with a nuclear envelope- has pores to let mRNA leave.
Contains DNA organised into chromosomes and also a nucleolus that manufactures ribosome subunits
Explain the structure and function of the cytoskeleton
A network of filaments and microtubules that maintain cell shape, anchor organelles and aid in cell and organelle movement
Explain the structure and function of the rough endoplasmic reticulum
The Rough ER is an interconnected network of microtubules that extend from the nucleus throughout the cell. Has ribosomes on its surface.
Its role is to transport materials throughout the cell. It also develops proteins from ribosomes.
Explain the structure and function of the smooth endoplasmic reticulum
Network of microtubules like rough er- without ribosomes attached.
Involved in production and transport of lipids as well as detoxification and glucose management in liver cells, and calcium storage in muscle cells
Explain the structure and function of ribosomes
Are a non membrane-bound organelle. Made of rRNA and protein. Can be free-floating, in cytoplasm or bound to the rough ER.
Site of translation where polypeptides are formed.
Explain the structure and function of lysosomes
A single membrane vesicle of over 40 hydrolitic enzymes. Made by the golgi apparatus.
Aids in breaking down material that enters the cell, or can fuse with damaged organelles to recycle them
Explain the structure and function of the golgi apparatus
A set of flattened stacks (cisternae)
Collecting, packaging, modifying and distributing cellular products- mostly proteins and lipids.
The cis side faces the rough ER and collects materials. The materials move to the trans side which forms vesicles of material to transport out of the cell
Explain the structure and function of mitochondria
A rod-shaped organelle throughout the cytoplasm. Approx size of bacteria, with DNA and ribosomes inside. Have a folded inner membrane that creates a fluid filled inner space.
Site of aerobic cellular respiration.
Explain the structure and function of chloroplasts
Found in algae and plants. Similar in size to bacteria, with DNA and ribosomes. Has an inner and outer membrane and inner membrane stacks that absorb light.
Site of photosynthesis
Explain the structure and function of the centrosome
A structure in eukaryotic cells that aid in cell division. A pair of centioles that assemble microtubules to move chromosomes. Only in animals, but plants have a centrosome region that instead produces microtubules
Explain the structure and function of vacuoles
inc. difference between plants and animals
Storage organelles formed by the golgi apparatus.
Plants have a large central vacuole that stores water and creates turgidity
Animals have smaller, scattered vacuoles that contain food storage, or waste and toxins to be expelled
Explain the difference between ribosomes in prokaryotes and eukaryotes
Eukaryotes: larger and denser, 80S ribosomes
Prokaryotes: 70S ribosomes
Both: made of two seperate subunits that clamp together in translation
What functions must a unicellular organism carry out to be classified as living?
- Metabolism
- Growth
- Reproduction
- Respond to stimuli
- Homeostasis
- Nutrition
- Excretion
- Movement
What are plasmids?
ONLY IN PROKARYOTES
Plasmids are extra circles of DNA which contain additional adaptive DNA
What is an amyloplast?
ONLY IN PLANTS
Organelle for starch synthesis and storage
What are specialised cells and tissues?
Specialised cells are cells that have changed structure to carry out a specific function within a multicellular organism.
Clusters of the same specialised cells are known as specialised tissue.
What is cell differentiation?
Cell differentiation is the process where a stem cell turns off unneeded genes and only expresses relavent genes for its function to become a specialised cell.
Cell differentiation can be triggered by changes in environment, but is also a regular part of embryo development.
What are some characteristics of animal cells that make them unique from other eukaryotes?
- No cell walls (flexible and round shapes)
- Small and many vacuoles (perform many functions)
- Able to store carbohydrates as glycogen in specialised cells
- May contain flagella or cilia
- Have centrioles that form the centrosome
What are some characteristics of plant cells that make them unique from other eukaryotes?
- Cellulose cell wall (angular shape)
- Chloroplasts (for photosynthesis)
- Large, central vacuole (stores carbohydrates and water, creates turgidity)
- Store carbohydrates as starch in amyloplasts
- No cilia or flagella
- No centrioles but still forms centrosomes
What are some characteristics of fungal cells that make them unique from other eukaryotes?
- Chitin cell wall for flexible shape and protection
- No chloroplasts
- Many small vacuoles with different functions
- Store carbohydrates as glycogen
- Can have cilia
- No centrioles but form centrosomes
How are the specialised cell ‘hyphae’ atypical?
- Long, one cell wide filaments that fungi produce
- Usually expand underground and play a role in water absorption
* Can be connected by cell walls for easy transport but some have evolved to have no cell walls separating them creating a long cell with multiple nuclei
How are the specialised cell ‘phloem sieve tube elements’ atypical?
- Form thin tubes to transport sugar in plants with pores separating individual cells
- Have minimal cellular components and rely on a companion cell to perform functions and supply energy
How are the specialised cell ‘skeletal muscle cells’ atypical?
- Single long cells with multiple nuclei to aid movement
- Long tubular cells that can expand and contract
- Have extra mitochondria to meet energy needs
How are the specialised cell ‘red blood cells’ atypical?
- Made by bone marrow and when specialise, they lose their nucleus
- This allows for a flattened shape and an increased SA:V ratio
- More haemoglobin can be close to the surface to collect and transport oxygen
How does the endosymbiotic theory account for the origin of prokaryotic organelles?
- Proposes that early eukaryotic cell engulfed a prokaryotic cell
- The prokaryotic cell is not consumed and remains functional inside
- The prokaryotic cell aids in energy production which provides a survival advantage
- Over time, the prokaryotic cell self-replicates inside the cell to make mitochondria
- Same occured to make chloroplasts
What is the evidence for the endosymbiotic theory?
Chloroplasts and mitochondria have:
* Double membrane (outer membrane acquired from endocytosis)
* Own naked circular DNA
* Own 70S ribosomes
* Have ability to self-replicate seperately to the cell
What allows for cells to self-differentiate in multicellular organisms?
Preferential expression of genes mean cells become specialised with a unique appearence and function.
What is a virus?
A virus is a non living particle that infects cells and reproduces inside of them
Common features:
* Small size
* No growth
* Nucleic acid as genetic material- inserted into host cells
* Protein capsid as outer layer
* No cytoplasm, organelles or usually enzymes
* Many have spikes
What is a capsid?
A simple protein coat that contains the genetic material of a virus.
* Much simpler than a cell membrane
* Can be the outer layer of a virus, or they can have an envelope made of host cell plasma membrane- helps with cell recognition
What is a prophage?
The combined nucleic acid of the viral and host DNA.
This forms during the lysogenic phase of the viral life cycle.
This means that when cell division occurs, the whole prophage is replicated.
Explain the differences between an outbreak, an epidemic and a pandemic.
Outbreak- spread of infection isolated to a small geographic area
Epidemic- outbreak that moves more quickly and across more area than expected
Pandemic- an epidemic that crosses many countries or is even worldwide
What forms can the genetic material of viruses exist?
Viruses can have DNA or RNA as genetic material
* RNA viruses can use RNA directly, or transcribe it into mRNA
* Retroviruses reverse transcribe RNA into DNA
Explain the structure of the virus ‘bacteriophage lambda’
Bacteriophage lambda is a virus that invades E.Coli bacteria
Structure:
* Capsid
* DNA as genetic material
* Tall sheath and base plate with pins and tall fibres
Function:
Tall fibres attach to host cell and tail sheath has proteins that help get through the host cell membrane
Explain the structure of the virus ‘coronavirus’
Coronavirus is a virus that invades human cells, especially the respiritory tract.
Structure:
* Spherical shape
* Single stranded RNA as genetic material
* Has envelope as well as capsid
* Capsid attached close to RNA
* Spike proteins on envelope
Explain the structure of the virus ‘human immunodeficiency virus’
HIV is a virus that attacks helper T cells (white blood cells) of humans, progresses AIDS
Structure:
* Capsid coat and outer envelope
* Identical RNA strands copied into DNA by enzyme ‘reverse transcriptase’
* Has both protein and carbohydrate spikes
Explain the basic sequence of a lytic life cycle
- Virus attaches to host cell
- Virus inserts its DNA/ genetic material into the host
- Host cell uses DNA to make viral parts
- The viral parts assemble into viruses
- The new viruses lyse the host cell and the viruses are released
Cycle begins again
Explain the lysogenic life cycle of a virus
- The lysogenic cycle is longer than the lytic cycle- can integrate back to lytic cycle BUT IS NOT INCLUDED
- Involves the integration of the viral DNA into the host DNA without being used to make viral parts
- This means the viral DNA can spread slowly through cell division
- If the viral DNA is released from the host DNA (by factors such as UV exposure, chemicals), then the lytic cycle is initiated
How might viruses be an example of convergent evolution?
Viruses have a wide variety of structures (especially nucleic acids), which suggest common ancestry is unlikely
Instead, they have likely evolved seperately and similarities are a result of convergent evolution whereby adaptive features (e.g spikes for attachment) were independently evolved)
