Final Flashcards
Sources of carbon for organisms
- requirements
Organic material is needed for cell activities – carbohydrates, proteins, lipids and nucleic acid
Carbon may originate from:
1. Autotrophic nutrition – carbon dioxide; “auto” cells are self-sufficient; humans can’t do this
a. Photoautotrophs – photosynthetic producers
• Plants, algae, & prokaryotic photosynthesis bacteria (cyanobacteria)
• Need water and minerals from soil and carbon dioxide from the atmosphere
2. Heterotrophic nutrition – Use preformed organic carbon sources
a. Consumers – live on compounds produced by photoautotrophs (they can’t cook)
• Decomposition – fungi and bacteria
• Direct consumption – eating other consumers/producers
Origins of photosynthesis
Began in cyanobacteria (photosynthetic bacteria)
• Early earth atmosphere had no o2 – cyanobacteria produced o2 to allow other organisms to live and evolve
Cyanobacteria – highly folded plasma membrane
a. Many pigments – can harvest light energy and convert to chemical energy/glucose
b. Same structure of the chloroplast membrane – endosymbiotic theory
- Chloroplasts were photosynthetic bacteria
- Cyanobacteria got trapped inside larger cell – created photosynthetic euks
Photosynthesis as a series of redox reactions
- where does o2 originate & water splitting
- potential energy
6Co2 + 6h2o + solar energy -> 6o2 + c6h12o6
Co2 is reduced, h2o is oxidized
- Electrons move h2o -> co2 and form glucose
- Oxygen is an oxidizer – co2 has more than h2o
Glucose is reduced
Oxygen is produced
a. Uses water as a reactant and a product
Water in product -> split to form O2 and 2e- for glucose
a. Two water molecules requires per a O2
- O2 originates in h20
- Initially thought o2 came from co2
b. Experimentation showed
- co2 oxygen -> glucose and water
- h2o oxygen -> oxygen gas waste
Potential energy
a. Photosynthesis
i. Increases from h2o (low) to glucose (high) – endergonic reaction (+G)
• H2o is the ultimate donor – low energy electrons
• Energy from sunlight lifts energy of electrons – increases potential energy
b. ETC
- Decreases from glucose (high) to h2o (low) – exergonic reaction (-G) to synthesize ATP
plants structures
- how many chloroplasts
- fluid of stroma
Chloroplasts – in euks; the site of photosynthesis
a. 30-40 chloroplasts/cell – lots of power for photosynthesis
- 1mm3 leaf = 500,000 chloroplasts
- Concentrated in mesophyll – middle tissue leaf structure
b. Double membrane
- Stroma – innermost liquid; thick fluid
c. Thylakoid – stacked within stoma; form grana/granum
- Membrane – contain chlorophyll pigments
• Pigments – green colour; absorb solar energy
• Analogous to the internal membranes of photosynthetic prokaryotes – structures are arranged differently
Energy drives photosynthesis
- Glucose – assembled from 2 3C intermediates
- H2o and o2 – waste products
Stomata – regulate entering of CO2 enters and exiting of O2 by opening and closing
Xylem – vessels transport H2O throughout; absorbed by the roots
Phloem – vessels that transport sugar to the roots & other nonphotosynthetic structures
Light reaction
- where does it occur
- what is the energy source - how does it act
- pigments & types of pigments
- photosystems
occurs within thylakoid membranes
Photo stage: solar energy (sunlight) -> chemical energy (ATP)
i. Light absorbed by chlorophyll is used to power the transfer of electrons from water to NADP+ -> NADPH + H+
Sunlight – electromagnetic radiation
- Light – travels in waves; has electrical and magnetic properties
a. Wavelength – the distance between crests; inversely related to energy - Visible light – 380nm to 750nm; seen as colour; drives photosynthesis
a. Behaves like it’s composed of photons
- Photon – has a fixed quantity of energy
b. Can be reflected, absorbed, transmitted
- Pigments absorb light energy – green colour is reflected (not absorbed)
c. Green – not able to be absorbed to perform work
Pigments – absorbs light energy; excite an e- to higher orbital
- Absorption of a photon – boosts the electron to an excited higher energy state
a. Energy of absorbed photon – must be exactly equal to the difference in energy between ground state and excited orbital
b. Excited state is very unstable – electron will drop back to ground state very quickly
i. Will emit photon if energy is not harvested – will be lower in energy than absorbed photon
- Some energy is lost as heat
- Emitted photon – creates fluorescent/light
c. When energy is harvested – used to fix carbon
Accessory pigments – allow absorption of an increased number of wavelengths
- Creates expanded absorption spectra and less waste
- Small structural differences between pigments – allow for increased absorption
3 types of pigments – each has a characteristic absorption spectrum
- Chlorophyll a – participates directly in the light reactions
a. Engages and delivers the energy – ultimate receiver of satellite pigments
b. Blue green – is reflected - Chlorophyll b – accessory pigment
a. Absorbs light in its spectra & sends to chlorophyll a
b. Olive green – reflected - Carotenoids – accessory pigments
a. Absorbs light in its spectra & sends to chlorophyll a
b. yellow/orange – reflected
c. Serve as photo-protectants – protects from UV radiation (can cause skin cancer)
i. Absorb and dissipate energy – DNA and other delicate molecules are preserved because energy is absorbed before it reaches them
ii. Energy would have otherwise damaged other pigments or react with oxygen
- Anti-oxidant properties
Photosystems – reaction center complexes within thylakoid membranes; consists of a pair of chlorophyll a molecules and light harvesting complexes
- Light harvesting complexes – have pigments a, b, and carotenoids bound to different proteins
a. Increased quantity and variety – allows light energy harvesting to occur over a greater surface area and an increased spectrum of absorption
i. Act as antenna
b. Photons are absorbed by pigments – transferred between pigments until chlorophyll a pair is reached in reaction center complex - Chlorophyll a absorbs light energy – boosts electron to a higher energy state
a. The electron is transferred to a primary electron acceptor
i. Redox reaction – primary electron acceptor is reduced
- Electron does not drop back down
ii. Converts light energy to chemical energy - Electron from chlorophyll a pair has been lost when excited
a. Water is split
- 1h20 -> 2H+ + 2e- + ½ o2
b. These 2 e- replace what’s been lost in chlorophyll a pair
Light reaction process
- how is atp produced
- potential energy difference
- products and reactants
- what allows water to split
- where else is NADPH used
**P680 and P700 are essentially identical but associate with different pigment proteins altering their electron distribution
Photosystem II – functions first
1. P680 – absorbs photons of light at 680nm wavelength
a. energy is passed pigment to pigment
i. Pigment electrons are excited – energy released excites nearby electrons when electron falls
2. Chlorophyll a pair is reached
a. P680 is excited -> P680* & transfers electrons to the primary electron acceptor
b. H2O splits into 2H+, 2e- and O (1/2 an O2) – enzyme catalyzes
i. O combines with another to form O2 – releases o2 gas as waste
ii. 2 e- are used to replace 2 e- that were excited from P680 by transfer of energy through pigments
3. Excited P680* electrons are transferred via ETC to photosystem I
a. Carriers in ETC – plastoquinone, cytochrome complex, and plastocyanin
i. Exergonic transfers (-G) as e- falls from excited state
ii. Energy released is used to pump H+ into thylakoid space/lumen – builds up proton gradient
iii. ATP synthase is on the lateral side – synthesizes ATP as H+ flow through
- Chemiosmosis
- 6 H+ per water molecule splitting = 1.5 ATP:
4 H+ pushed across cytochrome complex
2 H+ released from splitting of water
- Moves ATP into stroma
b. Plastocyanin passes to P700
Photosystem I
- Light harvesting complex excites electrons in chlorophyll a pair P700 forming P700*
a. Same process as PSII
b. P700* passes the electrons to an electron acceptor - Lost electrons of P700 are replaced with the electrons moving from PSII down the electron transport chain
a. Originates from h2o in PSII - Excited electrons from P700* move down a second electron transport chain
a. Transfers to ferrodoxin
i. No proton gradient is being created
b. Transferred to NADPH reductase – in stroma
i. Protons are transferred to NADP+ -> NADPH
- Electrons are higher energy than water they originated on – excited by photons
- NADPH is in stoma
ii. Phosphorylated electron carrier – we also use to make fats in cells
Reactants
i. Sunlight
ii. H2o
iii. NAD+
iv. ADP
Products in this stage
- Oxygen gas – waste
a. Water is split into 2 H+ and 2e-
b. 2 water molecules form an o2 gas molecule - NADPH – reactant for dark reaction in stoma
- ATP – reactant for dark reaction in stoma
a. Produced via photophosphorylation (chemiosmosis) – NOT oxidative - NO glucose
Cyclic electron flow and ATP synthase
- which photosystem
- what is not produced
Uses only photosystem I
Uses ferredoxin to move e- back to cytochrome complex – exergonic transfer used to push H+ into lumen
Recycles electron to produce ATP
No o2 or NADPH created – electrons do not fall
Lift -> energize -> collect -> come down -> lift
Calvin cycle
- purpose
- when it takes place
- metabolism
- products
carbon fixation step; occurs in stroma
Converts co2 to glucose
i. CO2 + ATP + NADPH -> C6H12O6
Light and dark reactions both take place in daylight
i. Dark reactions do not require light**
Anabolic cycle (TCA is catabolic)
i. Requires energy as ATP
ii. Requires a source of reducing power as -> NADPH
Doesn’t directly produce glucose
- Produces (3C) glyceraldehyde 3 phosphate (G3P) -> 2 G3P forms glucose
a. 3 turns = 1 G3P
- 3 co2 are fixed
b. 6 turns = 1 glucose
3 phases of calvin cycle
- potential energy
- where else is G3P and NADPH used
Phase I: carbon fixation
- Ribulose bis-phosphate (RuBP) fixed onto CO2
a. RuBP (5C) – must be present in cell for dark rxns to begin; must be replaced at the end
i. 5C RuBP + Co2 = 6C molecules
- Unstable – immediately splits into 2 (3C) 3-phosphoglycerate
- 3PGA – phosphate is on 3rd carbon - Fixation is catalyzed by RUBISCO – enzyme; most abundant protein on Earth
Phase II: reduction
1. 3PGA accepts a phosphate from ATP -> forms 1,3 bis-phosphoglycerate
a. Each consumes 1 ATP – 2 ATP per fixed carbon
i. Energy and phosphate – ATP from light reaction
b. 1,3 indicated placement of phosphate (carbon 1 and 3)
2. 1,3 bis-phosphoglycerate -> accepts 2 electrons from NADPH & releases one phosphate group
a. Each molecule: 1 NADPH -> NADP+ H+ (2 e-)
b. Forms glyceraldehyde 3-phosphate -> increased potential energy
i. Also formed in glycolysis
c. Only carbon that is fixated can be contributed to G3P
i. Only 1/6 net gain
- 3 cycles for 1 G3P
- 6 cycles for 2 G3P = 1 glucose
ii. 36 carbons per 6 cycles
- 6 carbons per glucose
- 30 carbons from RuBP – 5C x 6 cycles = 1 glucose
(30 carbons/5 = 6 RuBP)
- Recycling 1 5C RuBP – requires 1 ATP
(6 ATP per glucose)
iii. 15 carbons from RuBP per 3 turns
3. Per glucose
a. 12 ATP from 3PGA -> 1,3 bisPGA
b. 6 ATP from recycling RuBP
c. 12 NADPH from 1,3 bisPGA -> G3P
4. Per G3P
a. 6 ATP from 3PGA -> 1,3 bisPGA
b. 3 ATP from recycling RuBP
c. 6 NADPH from 1,3 bisPGA -> G3P
Phase III: ribulose bis-phosphate regeneration
- Per G3P
a. 5 G3P x 3 carbon -> rearranged to 3 (5C) RuBP
b. Requires 3 ATP - Per glucose
a. 10 G3P x 3 carbon -> rearranged to 6 (5C) RuBP
b. Requires 6 ATP
Photorespiration
On hot days the stomata are closed to prevent water loss -> decreases co2 uptake and photosynthetic yield
o Accumulation of o2 gas due to light reactions – o2 is not leaving
Photorespiration – RUBISCO binds o2
1. C3 plants – make G3P first in dark reaction; normal photosynthesis
a. Ex. rice and wheat
b. When binding o2 -> produces 2 carbon compounds
• Leaves the chloroplast
• Peroxisomes and mitochondria rearrange compound -> is immediately broken down
- Consumes O2 -> releases CO2
2. Occurs because RUBISCO can bind o2 or co2
a. Wasteful – decreases photosynthesis
• Consumes co2 instead of fixing it – decreases carbon fixation material
• Consumes o2 instead of releasing
• Does not generate ATP -> consumes ATP
• Does not produce sugar
Alternatives to carbon fixation
C4 plants – produce 4 carbon intermediates first instead of G3P
- Used in many plants – unique leaf anatomy is needed
- Two cells required
a. Mesophyll Cells – loosely arranged between the bundle sheath cells and the leaf surface
i. Meso is middle – fills the middle space of leaf
- Most common area for photosynthesis
- Most plentiful cell
ii. Co2 accumulates here
iii. PEP carboxylase – enzyme combines 3C PEP with co2 -> forms 4C oxaloacetate
- Higher affinity for co2 that Rubisco
- No affinity for o2 – eliminates competition
iv. 4C oxaloacetate -> 4C Maltate
- Maltate is transported to bundle sheath cells via plasmodesmata
b. Bundle Sheath Cells – arranged around the veins of the leaf; vascular tissue that provides water
i. No oxygen is present
ii. 4C Maltate loses 1 carbon as co2 -> 3C pyruvate
- Co2 is used as a substrate for rubisco -> enters into Calvin cycle
iii. 3C pyruvate -> converted to 3C PEP & moved back into mesophyll
- Costs 1 ATP – keeps concentration of co2 in bundle sheath cells high
- High co2 concentration prevents rubisco from binding o2
CAM plants – photosynthesis adapted to hot climates (ex. cacti)
1. Stomata are open at night and closed during the day – all gas exchange occurs at night to conserve water
- Opposite of standard behavior
2. CO2 is taken into the leaf at night -> plant fixes co2 into organic acids
• Mesophyll cells -> store acids made at night in vacuoles until morning
3. During daylight – light reaction can occur
• Solar energy – required for ATP and NADPH production
• Organic acids release CO2 – enters Calvin cycle & used to produce glucose in the chloroplast
Fate of photosynthetic products
- how much carbs are produced a year by plants
- how is some energy lost
- how is it stored and what structure use it
Photosynthesis produces chemical energy and carbon skeletons – used to make all major organic molecules of plant cells (anabolism)
a. Glucose used for
- Fats
- AAs & protein
- Carbohydrates
- Nucleic acids
b. All had to come from co2
Chemical energy
a. 50% is consumed as fuel for cellular respiration
- Glucose enters into glycolysis
- Produces ATP
b. Some is lost to photorespiration – wasteful reaction with oxygen
Leaves are autotrophic
a. The remaining plant structures receive these organic carbon structures via the veins – usually as sucrose
- Used for cellular respiration and anabolic reactions
Products
1. Glucose – stored as starch & main ingredient of the plant cell wall
- Starch – storage form
- Cellulose – cell wall
2. Excess sugar – stored in the roots, seeds and fruits
a. Energy/carbon supply for heterotrophs – we use glucose to supply our carbon requirements
b Plants produce 160 billion metric tons of carbohydrates per year – ultimate producers
• One metric ton=1000kg
• Reduces greenhouse gases
3. O2 production
Cell division
- sexual vs asexual
- accuracy
- immune responses to errors
Most cell division serves to divide one parent cell into two identical daughter cells
1. Asexual reproduction – produces photocopies of cell; does not introduce any genetic variation unless there is an error made
a. Mitosis in eukaryotes
b. Binary fission in prokaryotes
2. Meiosis – exception; sexual reproduction
a. Parent cell divides into 4 daughter cells – cell splits twice
• 2 copies of 2 genetically non-identical cells
Cell division is always a highly accurate, highly complex process – sexual and asexual
1. Can otherwise create errors/variants
a. Differences are seen as changes in immune response – need different medication to treat different variants
b. Mutation – sometimes differences are not noticeable; severity depends on change
2. RNA viruses – covid
a. Do it with their own machinery – lots of errors and mutations
• We do not replicate RNA in this way
Chromosomes
- genome
- proks vs euks
- chromatin - activity and degrees of condensation
- chromosomes
- proteins present
- how many genes
- species
Chromosomes – DNA & associated proteins in a complex
Genome – total cellular DNA content
Proks vs Euks
1. Prokaryotes have one single circular DNA molecule/chromosome
2. Eukaryotes have many linear DNA molecules/chromosomes
a. includes DNA in mitochondria and chloroplasts
b. Humans – have 2 meters of genomic DNA; organized onto 46 chromosomes
• 250,000x cell diameter – must be coiled when separating
o Needs to be able to fit within the nucleus
• Must be able to replicate this DNA – also must be able to separate into two equal daughter cells
Chromatin – DNA & proteins; long and thin
- Proteins – allow the maintenance of cell structure; also assist with DNA function
a. Allow the DNA structure to be kept highly ordered & compact - Active – transcribing to create mRNA & proteins
- Can exist in varying degrees of condensation – coiled, uncoiled, somewhere in between
Chromosomes – coiled chromatin; shorter and easily visible
1. Histone proteins – small balls that dna coils around; makes chromosomes
2. Present during division – must be duplicated to have enough cellular material present for 2 cells
a. Creates 2 identical copies – very specific; errors result in cells that are not identical
i. Sister chromatids – duplicate copies
o Attached via cohesin proteins & centromere
o Separate from each other during division – become chromosomes
Consist of 100s-1000s of genes
o Specify an individual’s traits
Number of chromosomes vary depending on species
o Humans have 46
o Dogs have 78
2 cell types in humans & how many chromosomes
- fertilization
- Somatic cells – diploid
a. All body cells except sex cells (sperm and egg)
b. Have 46 chromosomes in the nucleus
i. 23 pairs – one from each parent - The genes on each code for the same trait – may have different types; may be the same
- Gametes – haploid
a. Sex cells used for reproduction (sperm and egg)
b. Contain 23 individual chromosomes – haploid
i. One taken from each pair in random order
ii. Fertilization – 2 haploid cells form a diploid cell (46 chromosomes)
Mitosis
interphase vs mitotic phase
- how long is each phase
- beginning and end of S phase
- how many errors occur
- what percent of cell life
- mitotic spindle
- are centrosomes essential
- end result
A cell will always be in a phase of division
a. Daughter cells immediately enter into G1
b. Cells that do not divide again enter into G0
- G0 – dead end; does not move into S phase
- Ex. neurons
Interphase
1. 90% of cell’s cycle – most of the cell’s life is spent in this stage
o Does not involve actual division
2. Involves duplication of chromosomes & organelles – increase in cell size
o Intense metabolic activity
3. 3 subphases – all involve protein and organelle synthesis
a. G1: 4-6 hours
i. Cell grows and increases in size
b. S phase: 10-12 hours
i. S = synthesis of DNA
ii. Chromosomal duplication
• Beginning – single chromosomes
• End – all are sister chromatids
iii. Cell still continues to grow and increase in size
c. G2: 4-6 hours
i. Continues to grow and prepare for division
Mitosis phase
10% of cell’s cycle
1. Actual division of chromosomes – extremely organized and accurate
a. Errors occur approximately 1/100,000 divisions
b. No genetic variation – asexual division
c. Less than 1 hour to complete
2 subphases
1. Mitosis – the nucleus and all its contents, including sister chromatids, divide and form 2 daughter nuclei
a. 5 subphases
• Prophase
• Prometaphase – transition phase
• Metaphase
• Anaphase
• Telophase
o Cytokinesis overlaps with telophase -> Symbolizes completion of mitosis
2. Cytokinesis – division of all cellular contents, nuclei and organelles
a. begins before the termination of mitosis
Mitotic spindle form during prophase – consists of fibres made of microtubules and associated proteins
a. Stem from centrosomes – 2 in cell; dense region under microscope
- Centrosome is composed of 2 centrioles at a right angle to each other
- Plants do not have centrioles – nonessential for cell division
b. Cytoskeleton will partially disassemble to provide material for spindle to form
c. Made from tubulin
- Microtubules polymerize by increasing tubulin to elongate
- Depolymerize by removing tubulin to shorten
end result – 2 identical daughter cells with a nucleus, cytoplasm, and plasma membrane
o each will inter into G1
Homologous pairs
- identical in
- staining
- locus and allele
Chromosomes – are present in homologous pairs
1. 23 homologous pairs in somatic human cells – equates to 46 chromosomes
a. Pairs encode for same traits
2. Identical in length and centromere position
a. Staining chromosomes – the matching chromosomes of a homologous pair display identical pattern of stripes
3. Locus – location on a chromosome that a particular gene
a. Homologous pairs – contain a gene encoding the same trait at the same locus
• May be different versions of trait (allele)
4. One from mother and father of each type of chromosome
Sex chromosomes – exception to the homologous pair rule in the human cell
1. Human females have XX – homologous pair of sex chromosomes
a. All 23 pairs are homologous
2. Human males have XY – nonhomologous pair of sex chromosomes
a. 22/23 pairs are homologous
• Most genes carried on the X chromosome do not have a counterpart on the Y chromosome
• The Y chromosome is much smaller but carries a few genes that are not on X chromosome
Diploid after fertilization – one chromosome from each homologous pair and one sex chromosome is inherited from each our mother and father
- Somatic cells have 23 chromosome pairs
- 1-22 are called autosomes
- 23 is the sex chromosome pair
Karyotype
- what cells are used
- how are they ordered
visual display of homologous chromosomal pairs; an individual’s magnified chromosomes beginning with the longest and arranged in homologous pairs
The chromosomes viewed are condensed and doubled – metaphase of mitosis
a. Lymphocytes (WBC) are used to prepare a karyotype
- Chemically treated to begin mitosis
- Second chemical is added after a few days to arrest the cells in metaphase of mitosis
Amplify chromosomal size
a. They’re in a condensed phase – easier to see than when they’re uncoiled
- They’re in mitosis – they have sister chromatids
Gametes
- fertilization (what n)
Haploid (one set of chromosomes)
A sexually reproducing organism must have two chromosome sets – one from each parent
o Humans are diploid organisms – only gametes are haploid
Fertilization – the fusion of two haploid gametes (one sperm and one egg)
- Results in a diploid zygote – 2 chromosome sets
a. If gametes were diploid – would result in tetraploid zygote
b. Zygote divides by mitosis – produces mature organism
- Will produce its own haploid gametes - Down syndrome – one extra copy of chromosome
a. Must be a highly specific process
b. Tetraploid would result in many error in development
Human life – alternating diploid and haploid stages
a. Haploid – produced in meiosis
- Genetic variability
- Occurs in testes and ovaries
- Meiosis reduces number of chromosomes by half – divides twice after chromosomal duplication
N = number of individual types of chromosomes; signifies variety
- n = haploid
- 2n = diploid
a. 2 sets of chromosomes – 1 from mother and father - After S phase – twice as many; chromatids attached at centromere
a. Diploid – still 2n; NOT tetraploid
b. Haploid – still n
3 types of sexual life cycles
- Human/animal life cycle
a. Meiosis takes place in germ cells – produces gametes (sperm and egg)
i. Haploid phase is only unicellular
b. Fertilization produces a diploid zygote: n + n = 2n
i. Divides by mitosis to produce a multi-cellular organism - Plant/algae life cycle – contain haploid and diploid multi-cellular stages
a. Sporophyte phase
i. Multicellular 2n sporophyte – produces n spores by meiosis
ii. n spore – divides by mitosis to produce gametophyte
- gametophyte – multicellular haploid
b. Gametophyte phase – produces n gametes by mitosis
i. Gametes fuse – form 2n zygote
ii. Zygote divides by mitosis – produce sporophyte
- Sporophyte – multicellular diploid - Fungal life cycle – opposite of humans
a. n Gametes fuse producing a 2n zygote
i. Zygote – divides by meiosis producing n cells
- Zygotes divide by mitosis in animals
- Single celled zygote is the only 2n phase
ii. n cells – divide by mitosis to produce haploid multicellular adult
- Cells of the adult phase – divide by mitosis in order to produce gametes
5 phases of mitosis
Prophase
- Chromatin becomes coiled forming visible chromosomes
a. DNA replication is done in loose state during S phase – do not compact prior to prophase - The nuclear membrane and the nucleolus disappear – allows for accessibility of chromosomes
- Animal cells – centrosomes duplicate during interphase
a. Centrosomes duplicate during interphase (initially only 1)
i. Duplication – interphase
ii. Migration – prophase
- They begin side by side near the nucleus
- Opposite poles – signifies end of pro-metaphase & progression into metaphase
- Prometaphase – transition phase between prophase and metaphase
iii. Spindle microtubules will grow out from them
b. Spindle apparatus fully forms – includes:
- Aster – an array of short microtubules that project out from each centrosome
- Spindle microtubules
- Centrosomes - Proteins associated with the DNA of the centromere:
a. Centromere – middle region of coiled chromosomes
b. Kinetochore – proteins attached laterally on either side of the centromere
i. Each sister chromatid contains one
ii. Site of attachment of spindle microtubules
- Kinetochore microtubules – differ from nonkinetichore microtubules
- Microtubules shorten and separate sister chromatids
iii. Number varies according to species
Metaphase
- Metaphase plate – duplicated chromosomes align down the center of the cell
a. Prophase – not perfectly aligned down the center yet
b. Metaphase – centromeres are located midway between the spindle’s two poles - Asters – have elongated and contacted the plasma membrane; provides anchor
- Non-kinetochore microtubules – have elongated and contacted non-kinetochore microtubules originating at the other pole of the cell
- Creates tension to allow to pulling apart of sister chromatids
Anaphase
- Centromeres separate from one another pulling sister chromatids apart
a. Separase cleaves cohesins – between centromere; hold sister chromatids together
b. Chromatids move to opposite poles of the cell - Overlap between non-kinetochore microtubules is reduced
a. Motor proteins walk microtubules away from one another -> consumes ATP
- Elongates the cell by pushing spindle poles apart from one another
b. Microtubules lengthen simultaneously by addition of tubulin – polymerize at overlap - Complete when chromosome duplicates have reached opposite poles of the cell
Telophase & Cytokinesis
Telophase
1. The reverse of prophase
a. The nuclear membrane and the nucleolus reform
b. Chromosomes become chromatin – reactivated
c. Disassembly of the spindle apparatus – microtubules depolymerize
2. Mitosis is now complete – the identical daughter nuclei have divided
a. Daughter cells are not completely formed but nuclear material is identical
Cytokinesis – the division of the cytoplasm and its contents
- Occurs at the same time as telophase
- Animals
a. Cleavage furrow – shallow groove in surface of plasma membrane
i. Cytoplasmic side – actin forms contractile ring
- Interaction of actin and myosin cause ring to contract – results in deepening of invagination
- Both proteins have motor components
- Deepens until cell pinches into 2 complete daughter cells
ii. no cell wall - Plant Cells
a. Cell wall inhibits the ability of cleavage furrow formation – too much additional material
b. Golgi vesicles carry cell wall material
- Move along microtubules to the middle of the cell during telophase
c. Vesicles fuse forming a cell plate – creates cell wall down the center of the cell
- Surrounding membrane eventually fuses with plasma membrane – forms daughter cells
Binary Fission
- size of genetic material in proks
mode of cell division in prokaryotes
Cell grows to double the original size & pinches down the center – divides into two genetically identical daughter cells that are the same size as the parent cell
1. While cell elongates – chromosome simultaneously duplicates and goes to other side of cell
a. Smaller chromosome than euks – still 500x the length of bacteria cell; must be highly coiled
b. Replication begins at origin of replication (ori)
• 2 origins – division proceeds outward; shortens the amount of time DNA replication takes (as opposed to one)
c. Protein assistance is required to move chromosomes to opposite poles
2. Plasma membrane pinches inward and two identical daughter cells are created
Can occur in as little as 10 minutes – average of 1-3 hours
o Very efficient because they do everything at once
Evolution of mitosis
Mitosis followed binary fission – simpler unicellular prokaryotic mode of reproduction
a. Developed into unicellular euks – developed ability to do mitosis
b. Proteins used in bacterial binary fission are related to proteins used in mitosis
- Proteins that are used to move proteins are similar
- Shows common thread/evolutionary pathway
Single celled eukaryotes use mitosis – simplified euk
a. Ex: Dinoflagellates
b. Nuclear membrane remains intact
- Intermediate between binary fission and mitosis
Meiosis
- similarities and differences
- twins
- interphase
produces haploid cells
Many stages are very similar to in mitosis
a. Both are preceded by interphase – doubling of chromosome in S phase
Differences from mitosis
a. Mitosis has one cell division
- Initial cell is 2n
- Results in two 2n genetically identical daughter cells
b. Meiosis has two cell divisions
- Initial cell is 2n
- Results in four n genetically variable daughter cells
- 2 would be identical if crossover didn’t occur
Twins
o Identical – same zygote divides by 2x what it’s supposed to after fertilization
o Fraternal – 2 eggs are fertilized
Interphase Preceding Meiosis – same as mitosis
a. 2n cell doubles in size
o Organelles and content duplicated in G1 phase
o Chromosomes duplicated in S phase
o G2 ensures cell is ready for division
Meiosis stages
Meiosis I
- Prophase I – most complex; produces a lot of variation
a. Many of the same processes as mitosis
i. The chromatin coils & becomes visible as chromosomes (sister chromatids)
ii. The nuclear membrane and the nucleolus disappear
iii. The spindle apparatus forms – grows from centrioles
b. Synapsis occurs – new
i. Homologous chromosome pair up & form tetrads
- Each chromosome in homologous pair will attach to only one microtubule
ii. Tetrad – 4 sister chromatids are present; 4 individual, unique chromosomes will eventually result
- Will have 23 tetrads – mitosis has 46 “boxes”
c. Crossing over occurs – must be between homologous pairs
i. Chiasmata – attachment point between homologous pairs; place of cross over
- The lateral chromatids do not participate – too far apart
ii. Responsible for genetic variation – would otherwise have 2 sets of identical haploid cells
- Variation is produced because the homologues can carry alternate versions of a gene
- Ex: one homologue encodes brown hair and the other encodes blonde hair
- Crossing over occurs and the homologue encoding brown hair may now encode blonde hair and vice versa
- The homologues contain genes other than hair color so crossing over has created a different combination of gene types on the same chromatid - Metaphase I
a. Chromosome tetrads are aligned at the metaphase plate down the center of the cell
i. The sister chromatids remain attached by their centromeres
b. Spindle microtubules are attached to the kinetichore in preparation for cell division
i. Chromosomes are only attached to one spindle
- Spindle microtubules from one pole of the cell are attached to one homologue
- Spindle microtubules from the other pole are attached to the other homologue
c. Homologous pairs are held together in metaphase at chiasmata sites - Anaphase I
a. Homologous pairs separate at chiasmata from one another – NOT chromatids
i. They are completely random in their separation – mother and father version will be randomly divided
ii. The sister chromatids remain attached by the centromere
b. 2 haploid cells result from 1 diploid cell – only have one chromosome set due to the separation of homologues - Telophase I & Cytokinesis
a. Telophase may be incomplete – cell is going to divide again right away
i. Normally involves the reforming of the nuclear membrane and nucleolus
- May reform partially
ii. Spindle apparatus does not disassemble
b. During telophase I – haploid chromosome set have arrived at opposite poles of the cell
i. Each pole has 23 distinct chromosomes – present as sister chromatids
c. Cytokinesis occurs simultaneously – the cytoplasm and its contents are divided into two and the haploid daughter cells are formed
Interphase does not occur between Meiosis I & II
a. There is enough chromosomal content created in interphase preceding Meiosis I for 4 daughter cells
o They can also produce more after division
o There is no chromosomal duplication
b. The chromosomes may briefly uncoil and become active – more often goes directly into prophase II
Meiosis II – very similar to mitosis except cell that is entering is haploid
- Prophase II – looks the same as mitosis
a. Chromosomes will recoil if they have resumed activity since Meiosis I
b. The spindle apparatus will attach to the centromere of each duplicated chromosome
i. 2 kinetochore proteins & microtubules are attached per centromere – unlike meiosis I
c. Chromatids are NOT identical because crossover occurred in prophase I - Metaphase II
a. 23 sister chromatids are aligned down the metaphase plate
i. Mitosis – has 46 sister chromatids
ii. Metaphase I – has 23 tetrads - Anaphase II
a. Centromeres of the sister chromatids separate
b. Sister chromatids of each pair (individual chromosomes) move toward opposite poles of the cell - Telophase II & Cytokinesis:
a. Telophase – the nuclear membrane and nucleolus reform, chromosomes uncoil
b. Cytokinesis simultaneously occurs – separates cytoplasmic contents
i. Cleavage furrow
c. Results in 2 non identical haploid cells – due to crossing over
Mitosis vs meiosis
Differences
1. Mitosis – asexual reproduction
a. Functions in growth, repair and asexual reproduction
b. Has one cell division
• Daughter cells are diploid and genetically identical to the parent cell – no variability unless errors occur
2. Meiosis – sexual reproduction
a. Has 2 cell divisions
• 4 daughter cells are haploid and genetically distinct from the 2n parent cell
b. You have a random combo of mother and fathers
• Even if they are equal from mother and father – still not identical due to crossing over
c. All events unique to meiosis occur in meiosis I
• Meiosis II is essentially mitosis except haploid – you need an indicator
Similarities
o Mitosis and meiosis are both preceded by chromosomal duplication during S phase of interphase
Origins of genetic variation
- recombinant
genetic variation of sexual reproduction arises in a number of ways
- Independent Chromosomal Orientation
a. Arrangement of chromosomes in metaphase I is random
i. This arrangement effects the composition of gametes that result
ii. The chromosomes from the mother will often carry different versions of genes than the chromosomes from the father
b. During tetrad formation there is a 50/50 chance that the chromosome of maternal origin will end up on one side of the cell over the other
c. Two possible chromosome arrangements – there are four possible gametes that can arise
i. Total number of chromosome combinations = 2^n (n = haploid number)
- Human sperm + human egg = 64 trillion possibilities - Random Fertilization
a. Homologues carry the exact same genes at the exact same loci
i. Ex: C (brown) and c (white) are alternate alleles for mouse coat color and E (black) and e (pink) are alternate alleles for mouse eye color
b. Differences in gene alleles differentiate gametes from one another – any sperm gamete can be used in fertilization
i. Egg – will be whichever is that month
ii. Sperm – will have variability between each other & any of them can fertilize the egg
- Creates more potential for genetical variability - Crossing Over
a. The exchange of corresponding segments between homologous tetrads in prophase I
i. Chiasma – where they contact and cross over
- 2 nonsister chromatids attach
- plural = chiasmata)
ii. Produces recombinant – new chromosomal combinations
b. At chiasma – each gene on one homologue is precisely aligned with the same gene on the other homologue
i. There are many genes carried on a single chromosome
ii. In humans approx. 1-3 crossing over events occur per chromosome per meiotic division
Regulation of the euks cell cycle
- why is it important
- how often do cells divide
- how is division regulated (not the specific types)
Molecular control systems exist to make sure errors do not occur – must have high levels accuracy
o Timing and the rate of cell division are critical to normal cell development
o Unregulated growth – cancerous
Frequency/rate of cell division varies considerably
1. Varies depending on type of cells
a. Nerve, some muscle cells & cardiac cells don’t divide at all – anything that damages will compromise the organisms ability to survive
• Building muscle – adding more contractile protein within cell; you haven’t actually added more fibres, only fibrils
b. Skin cells are constantly dividing
Differences in division are introduced by molecular regulatory mechanisms
o Signaling molecules in the cytoplasm are important – typically proteins that trigger and control key events
o Checkpoints in G1, S, and G2 – internal and external
Types of regulation
- significance of G1 & G0
Checkpoints – occurs at G1, S, and G2
- G1 is the most important – most effective because it’s at the beginning of the cycle & prevents wasting energy in subsequent stages
a. If the cell passes this checkpoint – it will move on and be committed to divide
b. If the cell does not pass this checkpoint – it will enter into G0 and not go on to divide
i. Some cells remain in G0 for life – cells will no longer divide (ex. neurons) - Some cells are pulled out of G0 based on external cues and enter into normal division
a. Ex: growth factors that are released due to injury – tissue must be replenished
Cyclin and cyclin dependent kinases (Cdks) – 2 classes of regulatory molecules that work together
- Cyclin dependent protein kinases (Cdk)
a. Kinases are phosphorylators – activate and deactivate proteins via phosphorylation of molecules
- Important for go signals at G1 and G2 phases
- Addition of neg charged group changes the protein structure – will now have repulsive forces
b. Cdk is always present in the cell at constant concentration
i. Inactive – requires the attachment of cyclin to become activated (cyclin dependent)
ii. Cyclin is not always present
- Degraded after division – must be regenerated for division to occur again
- Activity will increase or decrease based on the presence of the cyclin partner - Cyclin increases in G2
a. MPF – Cdk attached to cyclin; activated form of kinase enzyme
- Triggers the movement of the cell past G2 in mitosis
- MPF phosphorylates and activates proteins and other kinases
b. MPF initiates mitosis
- Proteins that cause the fragmentation of the nucleus arrive and are activated – results in dissolution of membrane
- Assists with chromosome condensation and spindle formation
c. MPF switches itself off in anaphase
- Activates a process that causes destruction of its own cyclin – inactivates
- Kinase is still present within cell at high concentration as an inactive Cdk
Internal and external signals – used as signals at checkpoints
- External – detected by receptors on membrane
a. Ex. cancers that originate from foods - Internal – during anaphase sister chromatids must be perfectly aligned down the metaphase plate in order for the cycle to move forward
a. Regulatory complex is activated when they’re properly aligned
i. Activates a pathway that ends in separase activation (enzyme)
- Separase cleaves cohesins between sister chromatids
- Protects the chromosomal content of daughter cells
b. If it’s not aligned – cannot go into anaphase
Physical and chemical factors – external factors
- Physical – presence of absence of certain things
a. Lack of an essential nutrient will stop cell division – even if all other conditions are favourable - Chemical – growth factors are proteins released by cells to stimulate other cells to divide
a. >50 known types
b. Ex: platelet derived growth factor (PDGF)
- Made by platelets – not cells; broken up megakaryocyte cell fragments
- Needed for fibroblast division – cells in CT
- PDGF receptor is located on the plasma membrane of responsive cells
- Binding of PDGF to the receptor causes the cell to pass the G1 checkpoint and divide
- Occurs in the body to allow wound healing
- PDGF is not always present – will not stimulate cells without the receptor
- If you cut yourself – PDGF presence initiates mitosis
Density dependent inhibition – physical external factor
a. Crowded cells will stop dividing – contact on all sides of cell stops division process
- Division will continue until a single layer of cells forms on the inside of a container
- Removal of some of the cells cause those located around the border to begin to divide
- Repair until density inhibition is restored and cells are present on all sides again
b. Cell surface protein binds to the counterpart on the adjacent cell and inhibits the growth of both cells
Anchorage dependence – external physical factor
- Cell division will not occur unless cells are attached to a solid support
a. Ex: extracellular matrix or the bottom of a container
- Controlled by plasma membrane proteins & linked cytoskeleton
- Cytoskeleton is attached to cell membrane proteins and subsequently extracellular matrix - If not attached – inhibitory signal to prohibit division
Cancer cells
- why do they occur (what do they lack)
- when do they stop dividing
- how do they occur
- mortality
- chromosome number
- lymph nodes
- signalling molecules
- treatment
Cancer cells do not exhibit density dependence inhibition or anchorage dependence
1. Results in excessive division – invade healthy tissues
a. Lack normal growth factors – may have their own growth factors
• When cancer cells stop dividing – random points; atypical checkpoints
2. Immortal – with unlimited nutrients they will divide indefinitely
a. Normal cells – divide 20-50 times before aging and dying
Develop when a normal cell undergoes a transformation to cancer cell
1. We have cancerous cells all the time – your immune system kills it
2. If the immune system doesn’t recognize the abnormal cell it will proliferate becoming a Tumor – mass of abnormal cells
a. Benign – stays in one spot
b. Malignant – undergoes changes and moves to other parts of the body
• Metastatic cancer
• You have no control – the longer its left, the harder it is to get rid of
Cancer cells have an unusual chromosome number – they divide so often; errors are more likely to occur
1. Loose their ability to attach to surrounding cells and the extracellular matrix
a. Spread to nearby tissues & may enter blood/lymph and spread to other locations
• This is why lymph nodes are often removed in cancer patients – if cancer cell is present in lymph it indicates spreading
May produce signaling molecules that allow blood vessels to grow inward
a. Angiogenesis – blood vessel development
b. If there is an influx of blood – there has been an increase of blood vessels & often indicates presence of cancer cells
Metabolic ability and normal function are lost
May be treated with:
1. High energy radiation – more specific to cancer cells because they loose their ability to repair DNA damage
- Once dna is damaged – can’t be fixed
2. Chemotherapy – drugs are administered into the blood that target the cell cycle in actively dividing cells
a. Target anything that are actively dividing – health and cancer cells
• Causes alot of side effects
b. Poor selective toxicity
Mendels pea plants
- why did he use pea plants
- characters vs traits
- true breeding - part of plant that reproduces
- traits he studied
- hybridization
Garden peas have
- Many different versions available – more statistics can be produced
a. Ex: purple, white variants - Have very short generation times & produce a large number of offspring
a. Not the case for humans – 9 month generation; small number of offspring; ethical violations
Characters vs traits
a. Characters – varied heritable features; can be pass down generation
- Ex: flower color, hair color, eye color
b. Traits – the variant of a character
- Ex: purple flowers vs white flowers, brown eyes vs blue eyes, brown hair vs blonder hair
- There is an infinite amount of possibilities
Pea plants are self-fertilizing – mates with itself with only its own gene pool; no new genes and traits coming in
1. Each flower has male and female parts
a. Egg bearing carpel (only 1)
b. Pollen producing stamen
2. Mendel removed the immature stamen – allowed him to control gametes used in fertilization
a. He dusted the carpel with pollen taken from a different stamen – flower sperm was transferred
3. True breeding individuals – mate with itself; only produces more of itself
a. Always homozygous – can be dominant or recessive
• Many rounds of self pollination – will produce the parent variety only; all future generations will only produce the same colour as parent
• No variability in F2 generation if they are self pollinating
b. Self pollination – male and female gametes are from the same parent
• No genetic variation
Mendel studied characters that occurred in two traits
- Didn’t consider things that had more traits – kept simple
- Ex: purple and white flowers
Crossed two different true breeding plants – hybridized
a. 2 true breeding individuals form the parent generation (P gen)
b. F1 generation – hybrids from P gen
c. F1 self pollinated to produce F2 generation
Blending vs law of segregation
- how many times did Mendel try and what ratio did it show
Blending hypothesis – phenotypes of offspring will be the intermediate of the parent
- If the blending hypothesis were to hold true – a cross of a purple flower with a white flower would produce a daughter population with light purple colored flowers
- Blending was not observed in Mendel experiment
a. Purple flower and white flower are P gen – both are homozygous
- Purple is dominant, white is recessive
b. F1 generation – original purple colour
- All are heterozygous (Punnett square) – purple and white coexist
- Self pollinated
c. F2 generation – purple flowers are still present, but white flower reappears
- 2 heterozygous Punnett square – 3 purple & 1 white
- 705 were purple : 224 were white
- Blending has not occurred because white remains – it was only masked by dominant gene
The same experiment with 6 different characters & 2 traits each showed the same outcome
o Always 3:1 in F2 generation from dominant vs recessive
