Cells Progress Test 1 Flashcards
Characteristics that define life
MRS H CHARG
M Metabolism
R Reproduction
S Sensitivity
H Homeostasis
C Cellular organisation H Heredity A Adaption through evolution R Response to stimuli G Growth and Development
Scale of life extends from ( largest units to smallest)
m, cm, mm, um (micrometres), nm (nanometres)
Natural selection
A selective force acts on variation, triggering a change
3 Domains of life
Bacteria, Eukarya, Archaea
Endosymbiosis theory
The theory that 2 organelles in eukaryotes (mitochondria and chloroplasts) are derived from bacteria.
Endosymbiotic process
Eukaryotic cells were believed to have evolved from prokaryotic cells. The proposed ancestors of mitochondria were oxygen using, non photosynthetic prokaryotes. Proposed ancestors of chloroplasts were photosynthetic prokaryotes. Eukaryotic cells ancestors engulfed these prokaryotes and instead of breaking them down they were instead maintained. Overtime the they formed a relationship with the cell and became an organelle and dependent of the host. However both chloroplasts and mitochondria contain their own DNA and ribosomes and are able to make some proteins.
Prokaryotic cells contains which 2 domains
Bacteria and archaea
Differences between eukaryotic and prokaryotic cells
(Main) Eukaryotic cells contain membrane bound organelles but prokaryotic cells do not.
Eukaryotic cells contain DNA in a nucleus which is bound by a double membrane, prokaryotic cells contains DNA in a concentrated region which is not membrane bound called the nucleoid.
Macromolecules
Formed by polymerisation of smaller building blocks which join by covalent bonds.
4 Macromolecule types
Polysaccharides (complex carbohydrates), nucleic acid, proteins and lipids
4 Carbohydrate levels
Monosaccharides (single unit), Disaccharides (2 units joined together), oligosaccharides and polysaccharides (both complex carbohydrates)
2 Monosaccharide types and functions
- Hexose monosaccharides (6 carbons) - Building blocks in polymerisation to form larger / more complex carbohydrates by joining in a linear fashion.
- Pentose monosaccharides (5 carbons) - Don’t polymerise but are apart of larger molecules.
Disaccharides structure
Two monosaccharides joined together
Oligosaccharides structure
Several (3-10) monosaccharides joined together
Eukaryotic and prokaryotic cell size
Eukaryotic cells 10 - 100 um
Prokaryotic cells less than 5 um
Natural selection 4 requirements
- Variation: between members of a population
- Inheritance: traits passed genetically through replicating organisms
- Selection pressures: some individuals reproduce more than others based off these
- Time: successful variations accumulate over many generations
Polysaccharides structure and types
Many (>10) monosaccharides joined together.
3 key types :
Starch (in plants) - made up amylose and amylopectin
Glycogen (in animals) - has a more branched structure
Cellulose (in plants) - monomers are stacked to form a different structure
3 Functions of carbohydrates
- Energy storage molecules such as starch and glycogen
- Structure eg cellulose in cell walls
- Cell to cell recognition eg carbs on cell membrane recognise other cells and anything else around them
Nucleic acid structure
5 bases (adenine, thymine, guanine, cytosine and uracil) combine with sugars and a phosphate group to form a nucleotide. Repeating nucleotides make up the polynucleotide.
Difference between DNA and RNA
- RNA contains uracil instead of thymine bases.
- Sugar in DNA is deoxyribose whereas in RNA its ribose (which has an extra hydroxide group in second carbon position)
- RNA is a single stranded polymer chain whereas DNA is a double stranded polymer chain.
Purine bases and structure
Adenine and Guanine
2 ringed structure
Pyrimidine bases and structure
Cytosine and Thymine
Single ringed structure
Protein definition
Molecules by which cells perform their functions in the whole organism. They are the functional unit of the cell. Proteins are polymers of amino acids.
Protein functions (8)
- Structural
- Storage
- Contractile
- Catalytic
- Transport
- Toxic
- Regulatory
- Protective
Lipids characteristics
Lipids are the only macromolecules which are not polymers. They are heterogenous meaning they are all structurally different. They are hydrophobic - water hating. Lipids are made up of the building blocks glycerol, fatty acids and hydrocarbon rings.
Lipid functions
- Structural – Plasma membrane contains cholesterol and phospholipids
- Regulatory – lipid soluble hormones
- Energy – Triacylglycerol (stored fat)
5 things cells must do
- Obtain raw materials
- Remove waste products
- Manufacture cellular materials
- Generate energy
- Control mechanism - regulate these processes
Organelles purpose
- Provide special conditions for specific processes
- Keep incompatible processes apart
- Allow specific molecules to be concentrated. Membrane bound compartments allow the formation of concentration gradient.
- Package substances for transport or export
Plasma membrane function
Provides a semi-permeable barrier, which controls movement of substances into and out of the cell. This limits the size of the cell because the surface area to volume ratio must be optimal for diffusion to occur at the necessary rate to sustain life.
Plasma membrane structure
Formed by a phospholipid bilayer.
Hydrophilic heads interact with the aqueous environments inside and out of the cell. The Hydrophobic lipid tails come together to form the inside of the membrane. This allows lipid soluble molecules to pass through and stops the movement and hydrophilic molecules.
Fatty acids in plasma membrane affect on fluidity
The composition of fatty acids in the plasma membrane affects its fluidity. Unsaturated tails are kinky whereas saturated tails pack together. Therefore unsaturated fatty acids make the membrane more fluid.
Cholesterol function in cell membrane
Cholesterol is a fluidity buffer, resisting changes in the membrane fluidity due to changes in temperature. At high temperature the cholesterol stabilises the lipid molecules adjacent to it so their movement is restricted. At lower temperatures, it hinders the close-packing of phospholipids, lowering the temperature at which the membrane solidifies.
Simple diffusion
Passive movement of substances driven by a concentration gradient. No energy is required. Lipid soluble substances can cross the hydrophobic interior.
Facilitated diffusion
Passive movement driven by a concentration gradient. and so no energy is required. Hydrophilic molecules which require a transport protein (channel or carrier) can pass through the hydrophobic core.
Osmosis
Form of facilitated diffusion where water molecules are moved across the plasma membrane through channels called aquaporins. (Cells will osmoregulate to prevent swelling or shrinking).
Active Transport
Movement of substances against the concentration gradient. Energy is required. Allows internal concentration to be different to the concentration of surroundings.
Co-transport
Indirect active transport where one substance is pumped across the membrane using ATP energy. The concentration gradient is then used to power the movement of a second substance against its concentration gradient.
5 Membrane proteins and their roles
- Signal Transduction, messages relayed from ECM to inside of the cell.
- Cell recognition, proteins can recognise other cells.
- Intercellular joining, proteins are able to join cells together.
- Linking cytoskeleton and ECM, can help cells stay where they need to be.
- Transport.
Endomembrane system
A series of organelles that work together to synthesise, package, label and ship proteins and molecules.
Nuclear envelope function
Controls the entry and exit for the nucleus.
Smooth endoplasmic reticulum function
- Detoxification (breakdown drugs / toxins)
- Lipid synthesis
- Metabolism of carbohydrates
- Calcium storage
(The amount of SR is changed depending on demand).
Rough endoplasmic reticulum function
- Main role = protein synthesis. Membrane bound proteins synthesised in the ribosomes will enter the lumen (interior) of the rER. They will then be processed and folded. They will then leave the ER and travel to the golgi in their own vesicle.
(Rough due to ribosomes)
Golgi apparatus function
Receives, modifies, sorts and ships proteins.
Vesicles from the ER will arrive at the cis face and processed vesicles will leave at the trans face.
-Glycosylation involves adding carbohydrates to proteins.
- Sorting proteins involves adding molecular markers to proteins to ensure they accumulate in correct vesicles.
- Directing vesicles involves adding molecular tags to vesicles to direct them to correct location.
Vesicles function
Transport things around the cell.
Lysosomes function
- Degrade proteins, carbohydrates, lipids and nucleic acids and release products into cell.
- Digest unwanted cellular material (autophagy)
- Phagocytic vacuole
- Low ph allows function of hydrolytic enzymes
Endocytosis process
The process of taking things in at the plasma membrane.
Phagocytosis process
The process of taking in large food molecules. The cell membrane will form extensions which envelop the food particle and draw it in. This forms a phagocytic vacuole which is digested by lysosomes.
Pinocytosis process
The uptake of extracellular fluid. This is a nonselective process. The membrane will fold inwards allowing the ECF to flow in the forming vesicle which then pinches off the cell.
Receptor mediated endocytosis process
A form of pinocytosis, but uses receptors expressed on the cell membrane to select for solutes that may be present at low concentration in the ECF.
Exocytosis process
Transports material out of the cell or delivers it to the cell surface.
Constitutive exocytosis
A continuous release of proteins as they’re synthesised. It is ongoing and unregulated.
Regulated exocytosis
Will only occur upon receiving a stimulus. Common for the release of hormones and neurotransmitters as we don’t want these released constantly.
Cytoskeleton functions and 3 components that makes it up
- Structure, helps maintain the shape of the cell
- Supporting the organelles
- Allows movement of organelles
Made up of microtubules, microfilaments and intermediate filaments.
How is the cytoskeleton dynamic?
It can rapidly disassemble and reassemble to allow rapid change in cell shape.
Microtubules structure and function
Coiled chain that forms a tube. Composed of tublin subunits (a protein). May radiate out of an organising centre (centresome).
Function:
- Resisting compression which helps to maintain cell shape.
- Provide motility for flagella and organelles, ( ATP powered motor units will walk organelles along microtubules providing a pathways for vesicles / organelles).
Microfilaments structure and function
Double chain coiled into a rope like structure. They are a chain of actin subunits (protein) which can form linear or 3 dimensional networks.
Function:
- Resist tension
- Cortical network is the arrangement of microfilaments under the plasma membrane. It helps to make this area less fluid in order to maintain surface tension and thus cell shape.
- Interacts with motor proteins for cell movements eg actin and myosin sliding = muscle contraction.
Intermediate filaments structure and function
Made up of a variety of proteins such as keratin in hair, lamins in the nucleus, neurofilaments in neurons. They are supercoiled into cables.
Function:
- Very strong but less dynamic cable which resists compression.
- Helps maintain cell shape and anchor organelles.
- May remain after cell has died.
- Form more permanent structures eg neurons.
3 types of cell junctions
- Tight junctions
- Desmosomes
- Gap junctions
Tight Junctions structure and function
Branching network of sealing strands.
Holds cells together very tightly, forming a seal.
Prevents movement of molecules and ions between cells so they are forced to cross the cell membrane to move into the tissue.
Desmosomes structure and function
Intermediate filaments acting like rivets between cells.
Attachment between sheets of cells such as muscles
Gap Junctions structure and function
Forms a ‘tunnel’ or pore between cells, a point of cytoplasmic contact.
Allows ions and small molecules to pass from cell to cell.
Allows rapid intercellular communication.
Extra Cellular Matrix
ECM is made up of proteins, particularly glycoproteins (proteins with added carbohydrates) and collagen. These sit in the proteoglycan complex matrix (proteins with extensive sugar addition). The proteoglycans trap water within the ECM which helps to resist compression and retain tissue shape.
Fibronectins (glycoproteins) attach cells to ECM
Integrins are membrane proteins which connect the cytoskeleton to the ECM, providing a communication link.
Cell wall structure
The primary and secondary cell wall is mainly made up of cellulose (polymer of glucose).
Primary cell wall 2 phases
- Crystalline phase = Cellulose highly organised in long ribbon like structures to form microfibrils.
- Non-crystalline phase = Made of pectin and hemicellulose as well as extensin proteins.
Pectin in cell wall
Pectin is a branched polysaccharide which binds with water and has gel like properties.
Hemicellulose in cell wall
Hemicellulose in a heterogeneous group of polysaccharides which has branching side chains. Thus it is not as strong as cellulose.
Extension in cell wall
Extension proteins cross-link the crystalline and non- crystalline matrix which dehydrates the cell wall. This reduces extensibility causing the wall to become rigid and strong.
Cell wall synthesis
Rosettes are a protein complex which push through the cell membrane. They move along the cortical microtubules which they are attached to on the inside of the cell. As the rosettes move along they will lay down cellulose, forming a cellulose microfibril above the plasma membrane. Thus the orientation of the cortical microtubules heavily impact the shape of the cell.
Polysaccharides ( pectin and hemicellulose ) are transported from the golgi to the membrane in vesicles. Extensin proteins from the rough ER are also transported to the membrane in vesicles. These substances will be released via constitutive exocytosis.
Middle lamella
At the top of the cell wall there is a pectin rich layer called the middle lamella which is a sticky layer between plant cell walls.
Cell wall functions
- Regulating cell shape (cell morphology), orientation of microtubules influences shape. Randomly orientated = cell expands equally in all directions. Orientated about 1 axis, cell expands in 1 direction.
- Structural Support, Protoplast (membrane and contents of cell) pushes against cell wall making it rigid and gives the plant structure when it has sufficient water.
- Prevents excessive water uptake, pressure of the protoplast on the cell wall limits the amount the protoplast can expand.
Vacuole function
Plants large central vacuole is surrounded by a single membrane which is very selective of what enters and exits the cell.
The vacuole gives the cell structure and shape as it will push the cytoplasm up against the cell wall, building internal pressure and providing rigidity. This also keeps organelles close to cell surface for optimal diffusion distance.
It can perform lysosome like functions in plants.
Secondary cell wall nature
Secondary cell walls are produced only in mature cells where growth has stopped. They’re composed of multiple layers and are much thicker and stronger than primary cell walls, providing more structural support.
Secondary cell wall structure
Composed of more cellulose and less pectin than in primary cell walls.
Also contain lignin, a complex polymer that provides strength and rigidity and acts to exclude water.
Plasmodesmata function
Connections between cells that enable cell to cell communication. They’re pores in the cell wall through which the cell membrane, rough ER and cytoplasm are continuous. They allow the movement of small molecules but not organelles.
Major 4 energy requirements of the cell
- Mechanical work eg. motor proteins
- Make new materials eg. cell division
- Transport eg. active transport
- Maintain order
Mitochondria structure and function
Mitochondria has a double membrane with the inner membrane being highly folded into folds called cristae. The space in between the 2 membranes is called the intermembrane space and the space inside of the inner membrane is called the matrix.
Mitochondria is the site for cellular respiration, the formation of ATP.
Respiration equation and 3 steps
Glucose + oxygen -> Water + carbon dioxide + ATP
- Glycolysis
- Pyruvate oxidation and citric acid cycle
- Oxidative phosphorylation
Glycolysis process
Occurs in the cytosol
Glucose is split to produce 2 pyruvate molecules. This also generates 2ATP and NADH (store of high energy electrons).
Pyruvate oxidation and citric acid cycle
Pyruvate travels to the matrix. It is then converted into Acetyl CoA. In doing so NADH and CO2 will be generated. Acetyl CoA will then enter the citric acid cycle. From this cycle energy will be released as ATP. NADH, FADH2 and CO2 will also be generated.
Oxidative phosphorylation Part 1 - Electron transport chain
NADH and FADH bring high energy electrons to the inner mitochondrial membrane. The NADH electrons will begin to move through the protein complexes embedded in the membrane. As the electrons move through, energy is generated to pump protons (H+) from the matrix across the inner membrane. As the protons accumulate in the intermembrane space, a concentration gradient is formed.
Once the electrons have moved through the protein complexes their energy will be used to combine oxygen and hydrogen ions to produce water.
Oxidative phosphorylation Part 2 - Chemiosmosis
The inner membrane contains the protein complex ATP synthase which spans right across the membrane. The proton gradient generated will cause the protons in the intermembrane space to move through this protein by chemiosmosis resulting in the synthesis of ATP. A phosphate group is added to ADP in the synthesis of ATP.
ATP importance
ATP is an energy carrier molecule.
It is coupled to reactions in the cell to drive energetically unfavourable processes that will not occur spontaneously.
It allows for the controlled release of high amounts of energy.
Chloroplast structure
Chloroplasts have a double membrane as well as a third membrane structure called the thylakoid membrane. This is highly folded and arranged into stacks called grana. Within these stacks, the intermembrane space is called the thylakoid space. Between the inner mebrane and grana there is a colourless fluid called stroma. The thylakoid membrane contains membrane proteins involved in the photosynthetic electron transport chain. Among these are protein complexes called photosystems which contain chlorophyll, a green pigment that absorbs light.
Photosynthesis equation and steps
CO2 + H2O - (light) -> C6H12O6 +O2
- Light Reactions
- Calvin Cycle
Photosynthesis Part 1 - Light Reactions
Light energy is absorbed by the chlorophyll in photosystem II and excites the electrons, causing the movement of 2 electrons through the photosystem. These electrons leave the photosystem and move through a cytochrome complex, losing some of their energy. The energy lost is used to pump hydrogen ions across the membrane into the thylakoid space. The electrons then continue to photosystem I where they will be re-excited (ie high energy restored) by the light energy absorbed by this photosystem. These electrons leave the photosynthetic electron transport chain and are stored in NADPH molecules.
In order to replace the 2 electrons which moved through the chain, electrons are drawn from water at photosystem II, producing O2 and H+ as a byproduct. This ensures a continual chain as long as there is water and light available.
The high concentration of protons in the thylakoid space forms a proton concentration gradient. Thus protons will move across the membrane through the protein complex ATP synthase, generating ATP.
Photosynthesis Part 2 - Calvin Cycle
Fixation = 5 carbon molecules react with a CO2 molecule and splits into 2x 3 carbon molecules. Reduction = 3 carbon molecule is converted into a different 3 carbon molecule. NADPH and ATP from the light reactions are used to convert the 3 carbon molecule into a higher energy molecule called a 3 carbon sugar. One of these molecules leaves the cycle to be used to produce glucose. Regeneration = The other 3 carbon molecules will continue in the cycle and be converted back into the the 5 carbon molecule.
Nucleus structure and function
Nucleus is surrounded by a nuclear envelope which consists of an inner and outer membrane. Each membrane is a phospholipid bilayer. The membranes are continuous with the ER membrane. Spanning across these membranes are membrane proteins called nuclear pore complexes which control the movement of molecules into and out of the nucleus.
The Nucleus contains most of the cells genes and is the control centre of the cell.
Substances moving into and out of the cell
Moving out :
- mRNA = carries the information from the gene to ribosomes where the gene product is synthesised.
-tRNA = transfers the correct amino acids to the ribosomes based on the mRNA code.
- Ribosomal subunits = needed to build proteins
Moving in:
- Control signals = when to turn a gene on or off
- Building materials = building blocks needed to make RNA
- Energy for chemical synthesis
Nuclear Lamina
The inner surface of the nucleus is lined by the nuclear lamina. This is composed of intermediate filaments (permanent structures). This lining has 2 key functions:
- Maintain the shape of the nucleus
- Help organise the packing of the DNA.
Nucleolus
Only present within non-dividing cells.
It is responsible for making for making ribosomal RNA.
This combines with proteins to form ribosomes.
Organisation of DNA within the nucleus
DNA double helix is about 2nm in diameter.
DNA wraps around specific proteins called histones forming bead like structures called nucleosomes. This forms the 10nm fibre. Histones interact further to coil into a 30nm fibre. This fibre then loops to form a 300nm fibre. The formation of the nucleolus in non-dividing cells allows the DNA to unravel enough for transcription to occur.
During cell division the fibres condense into metaphase chromosomes which is what we see in karyotypes.
Euchromatin
DNA is less dense as it contains the genes which are actively being used by the cell. This is the state of an active gene as transcription factors do have access to the gene.
Heterochromatin
DNA is more dense as the genes are not being actively used by the cell. These appear darker spots in the nucleus. This is the state of an inactive gene as transcription factors do not have access to the gene.
Relationship between Euchromatin and Heterochromatin
The relationship is dynamic (constantly changing) depending on whats happening in the cell and which genes have been turned on or off. Thus different parts of the genome change between the forms.
Components of DNA
DNA is a polynucleotide comprised of repeating nucleotides connected by phosphodiester bonds. The phosphodiester bond is formed in a reaction between the 3’ OH group (OH group of the 3rd carbon on one nucleotide) and the 5’ phosphate group (attached to the 5th carbon of the next nucleotide). The 2 stands go in opposite direction but run parallel to each other so are said to be antiparallel. The stands form a double helix with the backbones forming the two ‘ribbons’ of the helix and the bases in the middle.
Semi-conservative DNA replication model
Each DNA stand in the double helix is used as a template for the synthesis of 2 new strands. Therefore the replicated DNA strands will contain one parental strand and one newly synthesised complimentary strand.
This is important for genetic variation as any mutations in the parental strands will be passed onto further generations.
2 ways which DNA can be repaired
- During replication using Exonuclease
2. After replication using Endonuclease
Exonuclease activity
An enzyme that can remove nucleotides only from the ends of DNA strands. During replication DNA polymerase III will check the newly inserted nucleotides against the template strand as it moves along in the 5’ to 3’ direction. If an incorrect base is detected, it will be removed by the 3’ to 5’ exonuclease activity. The correct base will then be inserted.
Endonuclease activity
An enzyme which can remove nucleotides from within the DNA strand. If an incorrect base is detected within the strand after DNA replication, the endonuclease enzyme can remove a large section of nucleotides including the error. DNA polymerase will then come along and use the 3’OH group to add nucleotides and fill the empty gap. In order to form a phosphodiester bond between the last newly inserted nucleotide and the neighbouring original nucleotide, a ligase enzyme will use the 3’OH group and 5’ phosphate group to form a bond.
PCR
A method of making a large numbers of copies of DNA so that there is enough material to work with.
