knowledge organisers unit 1 Flashcards
1
Q
What is water
A
A polar molecule which allows hydrogen bonds between molecules; giving water important properties
2
Q
Properties of water
A
- Solvent
- Metabolite
- high specific heat capacity
- high latent heat of vaporisation
- surface tension
3
Q
Function of water being a solvent
A
Polar molecules dissolve in water and are able to be transported
4
Q
Function of water being a metabolite
A
Water is a reactant in photosynthesis and hydrolysis, produced in aerobic respiration and condensation reactions
5
Q
Function of water having high specific heat capacity
A
Lots of energy required to change the temp of water so aquatic/cellular environments remain stable
6
Q
Function of water having high latent heat of vaporisation
A
Evaporative cooling
7
Q
Function of water having surface tension
A
Support and buoyancy
8
Q
What are proteins constructed from
A
20 types of amino acid.
9
Q
What do two amino acids linked form
A
A dipeptide
10
Q
What are organic compounds
A
The molecules of life, which are all complex compounds of carbon (all have C-H bonds)
11
Q
What is an R-group
A
a variable group of atoms
12
Q
What is primary structure
A
The order and sequence of amino acids in a polypeptide chain
13
Q
What are amino acids linked together by
A
Condensation reactions that form peptide bonds
14
Q
What is a secondary structure
A
The folding of a primary structure into an alpha helix or beta pleated sheet
15
Q
Why is secondary structure the shape that it is
A
The shape that the polypeptide forms due to hydrogen bonding between R-groups
16
Q
What is tertiary structure
A
The further folding of the alpha helix to form a more complex, compact, 3D globular structure
17
Q
Why are enzymes tertiary
A
Because the bonds maintain the shape of the active site
18
Q
How is tertiary structure shape maintained
A
By hydrophobic interactions between R-groups to form disulphide and ionic bonds
19
Q
What is quaternary structure
A
A combination of two or more polypeptide chains in secondary or tertiary form to form a globular shape/molecule.
20
Q
Function and example of fibrous proteins
A
Structural function e.g. keratin
21
Q
Function and example of globular proteins
A
Metabolic function e.g. enzymes
22
Q
Test for proteins
A
Biuret solution turns from blue to purple/violet colour when protein is present
23
Q
What are carbohydrates
A
Organic compounds containing carbon, hydrogen and oxygen. Source of energy in plants and animals
24
Q
What are monosaccharides
A
A simple sugar and a type of monomer. E.g. triose or pentose
25
What is triose
A monosaccharide with 3 carbons which is important in respiration and photosynthesis
26
What is pentose
A monosaccharide with 5 carbons which is important in nucleotides
27
What is hexose
A 6 carbon glucose which is an important hexose sugar and used in respiration
28
What are the two isomers of glucose
alpha glucose and beta glucose
29
What's the difference between aglucose and Bglucose
Alpha glucose has the OH group BELOW C1. Beta glucose has the OH group ABOVE C1
30
What's the disaccharide sucrose made of
glucose and fructose linked in a condensation reaction to form a glycosidic bond.
31
Function of sucrose
A transport sugar in plants
32
What's the disaccharide maltose made of
two alpha glucose molecules linked in a condensation reaction to form a glycosidic bond
33
What's the disaccharide lactose made of
galactose and glucose linked in a condensation reaction to form a glycosidic bond
34
Function of lactose
Sugar found in milk
35
What is the polysaccharide starch
A polymer of a-glucose used as a compact energy storage in plants with little osmotic effect
36
What is the polysaccharide glycogen
A polymer of a-glucose used as an energy storage in animals
37
What is the polysaccharide cellulose
A polymer of B-glucose, adjacent monomers are twisted through 180° to each other. Used as a strong structure for plant cell walls
38
Why are the adjacent monomers in cellulose twisted 180° to eachother
Allow hydrogen bonds between chains, forming microfibrils
39
What is the polysaccharide chitin
Same as cellulose but with some -OH groups replaced by nitrogen containing acetylamine groups. Strong, lightweight and waterproof for exoskeletons
40
Test for starch
Iodine solution turns from brick red to blue/black if starch present
41
Test for reducing sugar
In 80°C, reducing sugars reduce blue benedict's solution to a brick red precipitate
42
Test for non reducing sugars (sucrose)
They can't reduce Copper sulphate so benedict's won't work. Sucrose hydrolysed by boiling in hydrochloric acid to form glucose and fructose. Acid neutralised with sodium hydroxide then can give positive benedict's result since glucose and fructose are reducing
43
What is an inorganic ion
An ion that contains no more than one carbon atom e.g. magnesium for chlorophyll, iron for haemoglobin, and phosphate for nucleic acids.
44
What is triglyceride
A kind of lipid made of glycerol linked to 3 fart acid chains during condensation reactions to form an ester bond
45
What is phospholipids
A kind of lipid made up of glycerol linked to 2 fatty acid chains and a phosphate molecule. Hydrophilic head and hydrophobic tail which explain the plasma membrane lipid bilayer
46
Test for lipids
Mix with absolute ethanol then add equal volumes of water. Positive result = cloudy emulsion
47
Functions of lipids
Insulation, energy storage and protection
48
What are unsaturated fatty acids
Mono-unsaturated fatty acids have one carbon-to-carbon double bond. Poly-unsaturated fatty acids contain two or more carbon-to-carbon double bonds
49
What are saturated fatty acids
Have only single carbon-to-carbon bonds.
50
What does a high intake of saturated fats do
Contribute to heart disease as it raises the LDLs (low density lipoprotein) which increases the incidence of atheromas in coronary arteries.
51
What are ribosomes made of
Large and a small subunit constructed from rRNA and protein
52
What do ribosomes do
Involved in protein synthesis. Occur in a smaller 70s size in prokaryotes and 80s in eukaryotes.
53
What is the endoplasmic reticulum
A series of flattened sacs - double membraned cisternae leading on from the nuclear envelope.
54
Rough endoplasmic reticulum functions
Covered in ribosomes for protein synthesis; cisternae then transport the protein
55
Smooth endoplasmic reticulum function
Synthesis and transport of lipids
56
Vacuole contains and surrounded by...
Contains cell sap and is surrounded by the tonoplast membrane
57
What is the cell wall
A structure made from cellulose microfibrils and pectin
58
What does the cell wall do
- Fully permeable for the transport of substances.
- Provides strength to the plant.
- It communicated through the cell wall via plasmodesmata.
59
What does the golgi body do
Modifies and packages proteins.
- produces secreting enzymes.
- secretes carbohydrates.
- produces glycoproteins.
- transports and stores lipids
60
What are centrioles
2 cylinders of microtubules that form the spindle in cell division. Found in animal cells.
61
What does the cell theory state
New cells are formed from other existing cells and that the cell is a fundamental unit of structure, function and organisation in all living organisms
62
What are animal and plant cells
Eukaryotic cells which contain membrane bound organelles. DNA found within a nucleus, cell walls made of cellulose, 80s ribosomes, and aerobic respiration in mitochondria.
63
What does the endosymbiotic theory state
The presence of 70s ribosomes and DNA in both mitochondria and chloroplasts suggest they were once free living cells engulfed by ancient bacteria and therefore a symbiotic relationship was developed with them.
64
What is the nuclear envelope
A double membrane with pores that allow mRNA and ribosomes out of the nucleus
65
What is chromatin
DNA coils bound to protein codes for protein synthesis
66
What is nucleolus
rRNA and ribosomes are made here
67
Mitochondria function
Site of aerobic respiration and ATP synthesis. Cylindrical for a large S.A and reduced diffusion distance. Inner membrane folded into cristae which have stalked particles involved in ATP synthesis.
68
Why are mitochondria different shapes
Different stages of development or lying on different planes
69
What do chloroplasts do
The thylakoid membranes of the chloroplasts contain chlorophyll which is a pigment that traps light energy for photosynthesis
70
What are prokaryotes
Bacteria are prokaryotic cells. Contain no membrane bound organelles and gives some essential differences between prokaryotes and eukaryotes
71
Difference between prokaryotes and eukaryotes
- P have DNA free in cytoplasm, E have DNA in nucleus.
- P have 70s ribosomes, E have 80s ribosomes.
- P have peptidoglycan cell wall, E have cellulose cell wall.
- P have mesosome for aerobic respiration, E have mitochondria.
72
What is a virus
Not a living thing. Has no cytoplasm or organelles. It injects its genetic material into a living cell which then creates more virus particles
73
Structure of virus
Nucleic acids inside of the capsid (protein coat) DNA or RNA
74
Light microscope uses
Can be used to view eukaryotic and prokaryotic cells. Can magnify up to x2000
75
Difference between light and electron microscopes
Electron microscopes have a much higher magnification and better resolution. Which allows the ability to distinguish between different structures.
76
Calibrating a microscope
1. count how many epu fit into the stage units.
2. use the I A M triangle to calculate size of each epu.
3. convert into um by x1000.
77
What are tissues
A group of cells with the same structure and function working together
78
What are organs
A group of tissues working together to perform a particular function
79
What are organ systems
A system of organs working together with a particular role
80
What are organisms
All the systems working together forming a discrete individual
81
What are epithelial tissues
Continuous layers of cells on internal and external surfaces
82
Cuboidal epithelium
- lines the kidney tubules and ducts of salivary glands.
- one cell thick and cube shape
83
Ciliated/columnar epithelium
- composed of cells with cilia which transports substances like mucus in the bronchi and ova in fallopian tubes.
- cilia move and sweep substances along.
- columnar.
84
Squamous epithelium
- consists of flattened cells on a basement membrane.
- form walls of alveoli and line bowman's capsule of the nephron in the kidney
85
What is muscle tissue
Tissues able to contract
86
Skeletal muscle tissue
- attaches to and moves the skeleton.
- striated/striped.
- voluntary and powerful contraction but tires easily
87
smooth muscle tissue
- spindle shaped cells.
- contract rhythmically and involuntarily but less powerful than skeletal.
- found in skin and digestive/respiratory systems where it's responsible for peristalsis.
88
Cardiac muscle tissue
- highly specialised tissue.
- contracts without nerve stimulation and doesn't tire.
- myogenic - every cell beats rhythmically and continuously
89
Enzyme structure.
Tertiary structure proteins with active site held together by peptide, hydrogen, ionic and disulphide bonds
90
Lock and key theory
Substrate is perfectly complementary to active site. Enzyme remains unchanged at end of reaction
91
Induced fit theory
Lysozyme is proposed to function in this way. Active site and substrate are not fully complementary. When reactive groups align both areas change structure slightly. The bonds in the substrate weakens and reaction occurs at lower activation energy.
92
What are intracellular enzymes
Enzymes which work inside cells and extracellular enzymes are secreted from cells for use outside of the cell.
93
Factors affecting enzymes
- temperature
- pH
- substrate concentration
- enzyme concentration
94
How does LOW temp affect enzyme activity
At low temps, there's low K.E and so few successful collisions where the substrate is able to enter the active site of the enzyme and form products.
95
How does HIGHER temp affect enzyme activity
As temp increases, the kinetic energy increases so there are more collisions and enzyme-substrate complexes formed. Continues up to optimum.
96
How does temperatures ABOVE OPTIMUM affect enzyme activity
K.E. increases to a point where vibrations in the enzyme molecule weaken the bonds holding the active site together. Denatures
97
How does HIGH substrate concentration affect enzyme activity
Increase substrate will increase collisions and rate of reaction. But at some point, any further increase has no affect and rate of reaction plateaus as all the enzymes have full active sites; turning enzyme concentration into the limiting factor
98
How does LOW substrate concentration affect enzyme activity
At low concentrations, substrate is the limiting factor
99
How do competitive inhibitors work
Complementary in shape to the active site of an enzyme so prevent enzyme-substrate complexes by blocking active site.
100
How do non competitive inhibitors work
Bind to the enzyme at the allosteric site which alters the shape of the active site so no enzyme substrate complexes can be formed.
101
What do enzymes do to activation energy
Enzymes are catalysts so lower activation energy of reactions but remain unchanged in the reaction
102
What do small changes from the optimum pH do to enzyme activity
Small changes either above or below optimum make small reversible changes by reducing efficiency
103
What do large changes in pH do to enzyme activity
Large changes can disrupt ionic and hydrogen bonds in the enzyme, causing permanent changes to the shape of the active site: denaturing it.
104
How does increasing enzyme concentration affect activity
Increases rate of reaction as more active sites are available for reactions
105
What are immobilised enzymes
Enzymes attached to an inert matrix such as sodium alginate beads.
106
Advantages of immobilised enzymes
- increased stability so will denature at higher temperature and can be used efficiently over a wider range of pH.
- products uncontaminated with enzyme.
- enzymes easily added and removed, therefore giving control over reactions.
107
What can immobilised enzymes be used for
Used in biosensors and to create lactose-free milk
108
The effect of inhibitors on enzyme activity
Increase in substrate will decrease the effect of inhibitor and increase rate of reaction. But some of the enzyme is always affected so the rate is always lower than it would be without the inhibitor.
109
What is metabolism
Anabolic and catabolic reactions that are catalysed by enzymes
110
What are anabolic reactions
Building up molecules
111
What are catabolic reactions
Breaking down molecules
112
What is the fluid mosaic model
Singer and Nicholson proposed it for the structure of cell membrane. Fluid because phospholipid molecules within a layer can move relative to each other. Mosaic because proteins are of different sizes and shapes and form different patterns
113
How can cell membrane permeability be increased
- Temperature - increase vibrations of phospholipids, moving them further apart.
- Organic solvents - dissolve phospholipids
114
How do lipid soluble substances and small molecules move through the cell membrane
Can dissolve and move directly through the phospholipid bilayer
115
How do water soluble substances move through the cell membrane
Can't pass through the hydrophobic fatty acid tails so must use intrinsic proteins to pass through
116
Phospholipid bilayer structure
The hydrophilic phosphate heads of the phospholipids form the outer and inner surface of the cell membrane. The hydrophobic fatty acid tails of the phospholipids point towards each other in the centre of the bilayer
117
Extrinsic proteins
Found on either outer surface of the bilayer. The ones with sugars attached (glycoproteins) form the glycocalyx layer of the membrane which has a role in cell to cell recognition
118
Where is cholesterol found
Between the phospholipids making it more rigid and stable
119
What are intrinsic proteins
Proteins which span the whole phospholipid bilayer and can form channel or carrier proteins
120
What are channel proteins
Pores lined with polar/hydrophilic groups that allow charged ions through
121
What do carrier proteins do
Allow larger polar molecules through such as water-soluble sugars and amino acids. Binding of the molecules changes the shape of the protein moving the substance into or out of the cell. Polarity of proteins determines if they sit on the membrane or through it (extrinsic or intrinsic)
122
What is osmosis
The diffusion of water from a region of high water potential to low water potential across a selectively permeable membrane
123
What is water potential
The tendency of water molecules to move. Pure water potential = zero and becomes more negative as the concentration increases
124
Why are plant cells turgid
In a hypotonic environment, cells take up water by osmosis. The pressure potential of the cell increases as the cytoplasm pushes on the cell wall.
125
What is incipient plasmolysis
A cell in this state has lost enough water for the cell membrane to start being drawn away from the cell wall. This lowers pressure potential to 0
126
What does it mean when a cell is plasmolysed
Cells in hypertonic environment become flaccid
127
Why is it important for animal cells to be in isotonic solution (same conc inside and outside cell)
Because they lack a cell wall. Cells can burst in hypotonic and shrink in hypertonic solutions
128
What is tonicity
Refers to concentration of solute
129
What is hypertonic
Means higher concentration of solute and therefore lower water potential
130
What is hypotonic
Means lower concentration of solute and therefore higher water potential
131
What is isotonic
Same concentration of solute and the same water potential so no net movement of water between two solutions.
132
What is diffusion
The movement of molecules from a region of high concentration to a region of low concentration; down a concentration gradient. Passive process so requires no energy from ATP
133
Where does simple diffusion occur
Through the phospholipid bilayer.
134
What is diffusion rate increased by
-Higher conc gradient.
-Thinner membrane/shorter diffusion distance.
-Larger surface area.
-Smaller molecules.
-Increased temperature.
135
What do respiratory inhibitors like cyanide do to the rate of diffusion
Have no effect on rate of diffusion, since cyanide leads to lack of ATP which isn't required.
136
What is facilitated diffusion
The process of diffusion but for polar molecules or ions that can't pass directly through the phospholipid bilayer so protein channels or carriers are used
137
An increase in concentration difference across a membrane for facilitated diffusion will lead to
Lead to a maximum rate being reached due to the limiting effect of the number of channels available. This is a passive process so the respiratory inhibitor has no effect.
138
What is cotransport
A type of facilitated diffusion where two different substances use the same carrier protein at the same time. E.g. glucose and 2 sodium ions attaching to a carrier protein on the outer side of the membrane. This changes the shape of the protein to flip them inside the membrane and diffuse separately.
139
What is active transport
A process which moves molecules against a concentration gradient: from a low conc to higher conc. Requires energy in the form of ATP from respiration
140
What will the addition of a respiratory inhibitor do to active transport
As it relies on ATP the addition of respiratory inhibitor will also prevent transport as there will be no ATP available
141
Bulk transport types
Endocytosis and exocytosis
142
What is endocytosis
Two types: phagocytosis where solids enter the cell, pinocytosis where liquids enter the cell.
1. plasma membrane folds inwards.
2. plasma membrane engulfs the material.
3. vesicle formed from plasma membrane enters the cell
143
What is exocytosis
1. vesicle formed from the golgi moves towards the plasma membrane.
2. vesicle fuses with plasma membrane.
3. vesicle contents empty out of cell.
ATP required to move vesicles so it's an active process.
144
What is the general structure of a nucleic acid
Pentose sugar, phosphate group and nitrogenous base.
145
How is ATP formed
In an endergonic reaction. 30.6kJ of energy is stored in this bond and released when it's hydrolysed into ADP and Pi
146
What is ATP
the universal energy currency as its used to provide energy for all biochemical reactions in all living organisms
147
Why is ATP good
ATP releases energy in small usable amounts and travels easily to where it may be used for secretion, muscle contraction, nerve transmission or active transport.
148
What is RNA
A nucleotide linked together in a single stranded polynucleotide
149
Three types of RNA and functions
- messenger RNA (mRNA) = complementary copy of the DNA genetic code in the nucleus during transcription
- ribosomal RNA (rRNA) = forms ribosomes
- transfer RNA (tRNA) = carries amino acid at the 3" end and an anticodon arm to attach to the mRNA.
150
What is DNA made from
Made from one strand of nucleotides linked by hydrogen bonds between the bases to another strand that runs antiparallel to the first
151
2 types of bases in DNA
- purines: adenine and guanine.
- pyrimidines: cytosine and thymine.
152
What do the bases in DNA do
Pair up with hydrogen bonds (A-T, G-C). This complementary base pairing links the two strands and a double helix is formed.
153
Differences between DNA and RNA
RNA = ribose sugar, single stranded, A-U C-G bases, short polynucleotides.
DNA = deoxyribose sugar, double stranded, A-T C-G bases, long polynucleotides.
154
What is DNA replication
When cells divide to form new cells, they must receive a copy of the DNA. Therefore, chromosomes must be able to make exact copies of themselves. The replication fork is shown opposite and DNA replication occurs
155
Steps of DNA replication
1. DNA helicase breaks the hydrogen bonds between bases in the double helix.
2. This unwinds the DNA and exposes unpaired bases.
3. Free nucleotides in the nucleoplasm are bound to their complementary bases on the unzipped strand.
4. DNA polymerase joins the nucleotides together by condensation reactions between sugar and phosphate groups of adjacent nucleotides.
5. Eventually, 2 new DNA molecules are formed from 1 new and 1 old strand of DNA. This = semi conservative replication.
156
Steps of transcription
1. DNA helicase unzips a section
(gene) of the DNA by breaking
the hydrogen bonds between
complementary base pairs.
2. RNA polymerase links to the
template (coding) strand of DNA
and attaches mRNA nucleotides to
their complementary base pairs,
e.g. Adenine in DNA now pairs with the mRNA base Uracil, Cytosine
continues to pair with Guanine.
3. This copying stops at a stop sequence / codon.
4. The newly made premRNA then leaves the DNA.
5. Post-transcriptional modification of the pre-mRNA takes place to remove the non-coding introns, leaving only the coding sections (exons) in the mature mRNA. This leaves the nucleus to be translated into a protein in the cytoplasm.
157
Steps of translation
1. mRNA is a linear chain of three base codons. There are complementary anticodons on tRNA molecules.
2. When the mRNA leaves the nucleus, it attaches to the small subunit of a ribosome.
3. The large subunits of a ribosome have 2 attachment sites for tRNA. The ribosome holds the mRNA and the tRNA (which have attached amino acids) in position for the amino acids to form peptide bonds and create a polypeptide chain.
4. The codon on the mRNA (3 base
code) therefore determines the tRNA as the tRNA which attaches must have a complementary 3 base code. E.g. mRNA CGA, tRNA GCU.
5. The tRNA that matches the codon on the mRNA has a specific amino acid attached to the 3’ end of the tRNA molecule. The ribosome moves along the mRNA holding each tRNA in place until the amino acid attaches. The tRNA then leaves, the ribosome
moves along and the next tRNA
attaches to the next codon.
158
Experiment which gave evidence to theory of semi conservative replication of DNA
1. Grow bacteria with a heavy isotope of nitrogen. Centrifuge a sample – a heavy band is seen.
2. Remove bacteria with heavy DNA and place into a medium with light nitrogen and allow bacteria to divide. They will synthesise DNA with the nitrogen isotope available meaning their DNA will contain 1
new (14N) and 1 old (15N) strand, making it intermediate in density when centrifuged
3. Allow 1 more generation to grow and the hybrid strands will now be copied in a semi conservative way creating 50%
hybrid and 50% light DNA.
159
What is conservative replication
direct copying of the nucleotide sequence onto a new double
stranded molecule which would give one light and one heavy molecule in generation 1.
160
What is dispersive replication
where half the nucleotides are placed randomly in the DNA being
replicated to make new molecules which would give successively lighter molecules and therefore a band between hybrid and light in generation 2
161
What does Meselsohn and Stahl's experiment disprove
Conservative and dispersive replication
162
What is the genetic code
A linear universal code for the production of polypeptides
163
What happens during post transcriptional modification
exons can be spliced (joined) together in different orders leading to formation of different
polypeptides. It may be that one gene-one polypeptide theory is
not entirely correct.
164
Why is the genetic code called degenerate
A change in code doesn't always mean a change in amino acid. As there are 64 possible triplet codes for the four cases so some amino acids have more than one code
165
How can new polypeptides be modified
by the addition of carbohydrates, lipids or phosphate or can be combined together, e.g.
haemoglobin.
166
What is the cell cycle
A natural cycle of events that occur in the life of a cell. Most of the time the cell remains in interphase
167
What happens if the genes which control cell cycle are damaged
Lead to uncontrolled mitosis, and this rapid replication of cells can form tumour which cause cancer (due to oncogenes)
168
What does mitosis do
Produces cells which are genetically identical to the parent cell: giving genetic stability
169
Why does mitosis occur
Growth, repairing damaged cells, replace old and worn out cells, asexual reproduction
170
How do haploid cells (single set of chromosomes) divide
Can only divide by mitosis
171
What happens during interphase
- replication of organelles like mitochondria and chloroplasts which have their own DNA.
- new organelles made.
- synthesis of ATP and proteins.
- increase in cell size.
- replication of DNA begins
172
Prophase steps (mitosis)
- Chromosomes CONDENSE and become VISIBLE.
- Centrioles move to OPPOSITE sides of the cell in animal cells.
- SPINDLE forms from microtubules.
- Nuclear envelope DISINTEGRATES
173
Metaphase steps (mitosis)
Centromeres of chromosomes attach to spindle and line up on the equator
174
Anaphase steps (mitosis)
- Spindle fibres SHORTEN
- Centromere SEPARATES and individual chromatids are pulled to the poles; centromere first.
175
Telophase steps (mitosis)
- Spindle BREAKS down.
- Chromosomes UNCOIL.
- Nuclear envelope REFORMS.
176
What is cytokinesis
The division of the CYTOPLASM to create the 2 new genetically identical cells
177
Differences in cytokinesis in plants compared to animal cells
In plants there are no centrioles, and a cell plate develops from the centre out instead of a cleavage from outside in like in animal cells
178
Where does meiosis take place
In gonads (reproductive glands). In 2 different cell division evens after interphase
179
What does meisosi do
Produces cells which are haploid for sexual reproduction (gametes)
180
Difference between mitosis and meiosis
- 1 nuclear division MIT, 2 nuclear divisions MEI.
- 2 cells formed MIT, 4 cells formed MEI.
- Genetically identical daughter cells MIT, genetically different daughter cells MEI.
- No crossing over MIT, crossing over at chiasmata MEI
181
Prophase 1 steps (meiosis)
- Chromosomes form bivalents (pairs of homologous chromosomes)
- Arms of chromatids cross over at chiasmata and genetic material exchanges between homologous chromosomes; increasing variation in inherited genomes
182
Metaphase 1 steps (meiosis)
- Homologous chromosomes arrange themselves in pairs along equator.
- Independent assortment occurs here where the homologous chromosomes from both parents arrange themselves randomly along the spindle facing each pole.
183
Anaphase 1 steps (meiosis)
- Chromosome bivalents separate as each chromosome is pulled by its centromere towards the opposite pole.
184
Telophase 1 (meiosis)
- nuclear envelope reforms around the chromosomes at the poles.
- in meiosis, prophase 2 occurs after telophase 1.
- as the chromosome pairs have separated, chromosomes are no longer in pairs and the cells are haploid.
185
Stage 2 of meiosis and cytokinesis
Events occur in each new nucleus exactly as they do in mitosis. Cytokinesis then occurs to result in 4 genetically varied cells.
