UNIT 1 - Cells Flashcards
(107 cards)
1
Q
What is the difference between unicellular organisms and multicellular organisms?
A
unicellular are single-celled and can carry out all of the functions of life independently while multicellular have specialized cells to carry out specific functions
2
Q
What are the principles of cell theory?
A
- all living organisms are composed of cells.
- cells are the smallest units of life.
- cells come from pre-existing cells, by division, and therefore new cells cannot be constructed from non-living chemical substances.
- the cell contains inherited information (genes) that are used as instruction for growth, functioning and development.
- cells are the site of all chemical reactions of life (metabolism).
3
Q
Give examples of limitations to cell theory (2-4).
A
- single cell capable of all life processes (ex. Amoebae)
- multi-nucleated (ex. muscle cells)
- can reproduce only when in control of a host cell (ex. viruses)
- no cell wall
4
Q
What categories of unicellular organisms are there?
A
- bacteria
- protozoa
- some fungi
- some algae
ex. euglena, paramecium
5
Q
List the functions of life with a brief explanation of each.
A
nutrition - obtaining food, to provide energy and materials needed for growth.
metabolism - chemical reactions occurring inside the cell.
growth - an irreversible increase in size.
response/sensitivity - perceiving and responding to changes in the environment.
homeostasis - keeping conditions inside the organisms within tolerable limits.
reproduction - producing offspring either sexually or asexually.
excretion - releasing toxic/harmful substances.
6
Q
What is differentiation?
A
The development of cells in different ways to perform different functions.
7
Q
What is the difference between tissues and organs?
A
a tissue is a group of simmilar specialised cells to perform a particular function whereas an organ is a collection of different tissues which perfom a specialised function.
8
Q
How do cells in multicellular organisms differentiate?
A
by expressing some of their genes but not others.
9
Q
What is the cost of specialization of cells?
A
that they are efficient at carrying out their particular function (ex. transport) but they are totally dependent on the activities of other cells.
10
Q
What are emergent properties in a multicellular organism?
A
arising from the interaction of component parts, i.e. the whole is greater than the sum of its parts.
11
Q
What is the main difference between light and electron microscopes?
A
light microscopes use light to form an image, while electron microscope uses electrons passing through the specimen.
12
Q
How to calculate the magnification of the microscope?
A
size of image/size of specimen.
13
Q
What is the surface area to volume ratio?
A
by the principle of surface area to volume ratio which states that larger cells have less surface area to bring in the materials and get rid of the waste that volume allows to be brought/rid
therefore
they change shape to long and thin or/and have infoldings/outfoldings to increase surface area.
14
Q
What does reproduction allows in cells?
A
growth
replacement of dead/damaged cells
15
Q
What are stem cells?
A
populations of cells within organisms that retain their ability to divide and differentiate into specialized cells.
16
Q
What is binary fission?
A
a reproductive process in prokaryotic cells that involves replication of the single circular chromosome -> two copies of which move to opposite ends of the cell and cytokinesis follows. It creates two genetically identical daughter cells.
17
Q
What is bacterial conjugation?
A
a process where DNA is transferred from one bacterium to another.
donor cell pulls itself close to the recipient cell by using sex pilus, then DNA is transferring between cells (in most cases in the form of a plasmid)
it enables genetical variation in prokaryotic cells
18
Q
List characteristics of a prokaryotic cell and explain in short what are they responsible for.
A
capsule - protection, jellylike outer coating.
cell wall - made of peptidoglycan, protects and maintains the shape of the whole cell.
plasma membrane - controls the movement of materials into and out of the cell, role in binary fission.
70S ribosomes - sites of protein synthesis.
nucleoid - region containing non-compartmentalized DNA as a single, long, continuous circular thread (bacterial chromosome), involved in cell control and reproduction.
fimbriae/pili - attachment, sexual reproduction (sex pili only!).
flagella - locomotion
cytoplasm - all cellular processes occur within
plasmid - additional genetic material, small DNA molecule (ex. for antibiotic resistance)
19
Q
List 6 differences between prokaryotic and eukaryotic cells.
A
- prokaryotic has naked DNA, while eukaryotes have it wrapped around histone proteins to form nucleosomes.
- DNA in cytoplasm in prokaryotes and in eukaryotes enclosed in a nuclear envelope.
- in prokaryotic cells DNA is circular, in eukaryotes linear.
- in prokaryotic cells there are no membrane bound structures, in eukaryotes there are (such as mitochondria, ER, Golgi apparatus).
- plasmid present in prokaryotes, no need in eukaryotes.
- smaller 70S ribosomes in prokaryotic cells, larger 80S ribosomes in eukaryotic.
20
Q
Why is compartmentalization important in eukaryotic cells?
A
to enable chemical reactions to be separated and occur simultaneously.
21
Q
List organelles of the eukaryotic cell.
A
- cytoplasm
- endoplasmic reticulum (smooth and rough)
- 80s ribosomes
- lysosomes
- Golgi apparatus
- nucleus
- chloroplasts
- vacuoles
- peroxisomes
- centrosomes
22
Q
What does nucleus consist of and what are the particular functions of its elements?
A
nuclear envelope/membrane with pores - allows compartmentalization, however, through pores exit small subunits of ribosomes.
chromatin - uncoiled chromosomes spread through the nucleus.
nucleolus - ribosomal RNA (rRNA) is synthesized from instructions in the DNA, also proteins imported from the cytoplasm are assembled with rRNA into large and small subunits of ribosomes.
23
Q
How are mitochondria built (with functions)?
A
double membrane
inner membrane folded intro cristae - site of chemical reactions
matrix - site of chemical reactions, fluid within
ribosomes 70S
DNA in circular chromosome - some autonomy within the cell
intermembrane space
proton pumps and ETC and ATP synthase
24
Q
What is the general function of mitochondria?
A
ATP PRODUCTION
POWERHOUSE OF THE CELL
btw cells with high energy requirements = lots of mitochondria (ex. muscle cells)
25
How is endoplasmic reticulum built and what is its function?
- tubes and flattened sacs.
- continuous with plasma and nuclear membrane.
- ribosomes on rough endoplasmic reticulum - responsible for protein synthesis.
- no ribosomes on smooth endoplasmic reticulum- site for lipid and carbohydrate metabolism (hormone synthesis).
most cells contain both sER and rER with rough closer to nuclear membrane.
26
How is GOLGI apparatus built?
flattened membrane sacs - cisternae.
membrane-bound vesicles
cis side - receives products form ER and moves to cisternae.
trans side - has small vesicles that carry modified materials to wherever they are needed inside or outside the cell.
27
What is the main function of Golgi apparatus?
to collect, package, modify and distribute proteins.
28
What is a lysosome, where is it created, how it is built and what's its function?
enzymes that many eukaryotic cells use to digest (hydrolyze) macromolecules
its created in the Golgi apparatus
does not have any internal structures, just a sac bounded by a single membrane containing up to 40 different hydrolitic enzynmes that catalyse the breakdown of proteins, nucleic acids, lipids and carbohydrates.
they fuse with old/damaged organelles to break them down to recycle the components, also involved in digesting the products brought into by phagocytosis.
29
What is and what is the function of a peroxisome?
its a self-replicating organelle containing oxidative enzymes (e.g. catalase).
it gets rid of the toxic substances.
30
How are ribosomes made and what is their function?
they are made of a small and large protein subunit and ribosomal RNA synthesized in the nucleolus.
they synthesize proteins.
31
What is a centrosome made of, where does it occur and what's its function?
its made of a pair of centrioles at a right angle (composed of microtubules)
it occurs in animal cells near the nucleus
assemble microtubules (important for cell division)
32
What do chloroplast consist of, where do they occur and what is their function?
each chloroplast has a sustem of flattened membranous sacs - thylakoids containing chlorophyll
a stack of thylakoids is called granum (pl grana), its a double membrane bound organelle, the fluid inside is called stroma, they contain 70S ribosomes and DNA which makes them semi-autonomous organelles.
they occur exclusively in plant cells, especially in leaves
they are a site of photosynthesis
33
What vacuole consist of, what's its function and where does it occur?
vacuole is made of a membrane - tonoplast and is filled with a fluid called cell sap
it serves as a storage area (of organic molecules and inorganic ions and water obvsly)
it occurs in plant cells and takes much of the space
(btw in young cells there are many smaller that later assemble into one large one)
34
What is a plant cell wall made of, what's its function and how does it allow the movement of molecules?
cellulose
its rigidity helps to support and protect the plant, maintains the shape
its freely permeable (porous) so it has no direct effect on the movement of molecules into and out of the cell
35
List 6 differences between animal and plant cell
- plants have plastids, animals no
- plants have a cellulose cell wall, animals only a membrane
- plants have a large central vacuole, animals small and temporary if any
- plants do not have centrioles, animal yes
- animal cells have cholesterol in their membrane, plants no
- plant cells store excess glucose as starch whereas animal cells as glycogen
- generally plant cells have a fixed regular shape, animal cells amorphous shape
36
What is the Gram staining method, which bacteria retain their color and which do not and why is that?
its a useful way of differentiating two types of Eubacteria
Gram-negative bacteria do not retain the colour where the dye crystal violet is added because they have large amounts of peptidoglycan(murein) in their cell walls
Gram-positive bacteria do not and therefore they retain the dye and appear purple
37
What is a fungi cell wall made of?
chitin
38
What is yeast cell wall made of?
glucan and mannan
39
What is algae cell wall made of?
cellulose
40
What is a animal cell wall made of?
NOTHING, because they do not have one
however the plasma membrane is a mixture of sugar and glycoproteins
41
What is in general the plasma membrane made of?
almost entirely of proteins and lipids, with small amounts of carbohydrate
42
What is the current, correct model of the structure of a plasma membrane called and why?
The fluid mosaic model
bc the lipids and proteins are like pieces of a mosaic that can rotate and move sideways as in a fluid
43
What does it mean that the plasma membrane is amphipathic?
one part of it is hydrophobic and the other is hydrophilic
44
How is a phospholipid constructed and how do the amphipathic properties correspond with that?
it has a head composed of a glycerol group with one ionised phosphate group is attached, it is highly polar bc of the organic alcohol with phosphate and therefore water soluble - hydrophilic
contrary are the two, long fatty acid tails that are not water soluble (bc they are non-polar), one tail is saturated (straight) while the other is unsaturated (double bond, curved) - hydrophobic
45
What happens when phospholipid molecules get in contact with water and what when they are mixed with water?
a phospholipid molecule has a hydrophobic tail - which repels water - and a hydrophilic head - which attracts water
phospholipid molecules in contact with water from a monolayer, with heads dissolved in the water and the tails sticking outwards.
when mixed with water, phospholipid molecules arrange themselves into a bilayer in which the hydrophobic tails are attracted to each other.
46
Based on what is the attraction between hydrophobic hydrocarbon tails in the bilayer and what are the consequences of that?
its based on van der Waals forces that are not very strong
therefore making the bilayer a fluid and flexible membrane with variable shape and enabling endocytosis
47
What proteins are present in the plasma membrane? Describe them.
Globular proteins (named for their approximately spherical shapes and are the most abundant proteins in nature):
- integral proteins - are embedded in the lipid bilayer
- peripheral proteins - attached to the surface
48
Where are the carbohydrate molecules present in the membrane?
glycoproteins - they attach to proteins
glycolipids - they attach to lipids
glycocalyx - form it
49
What is the glycocalyx and what are its functions?
The glycocalyx is a highly-hydrated fibrous meshwork of carbohydrates that projects out and covers the membrane of endothelial cells, many bacteria and other cells.
extracellular polymeric material produced by various cell types and is also known as the "sweet husk of the cell."
Functions:
- cell-cell recognition
- receptors site for chemical signals
- binding of cell into tissues
- mediates cell attachment,
- retains humidity during exposure to dry environments
- protects against molecular and cellular antibacterial agents (antibiotics, surfactants, bacteriophages, phagocytes)
50
Where does cholesterol occur, what is it, how is it built and what are its functions?
exclusively in animal cells
it has a hydroxyl group that makes the head polar and hydrophilic therefore attracted to the phosphate heads
carbon rings
non-polar tail - attarcted to the phospholipid tails
its a stereoid (natural or synthetic organic compounds characterized by a molecular structure of 17 carbon atoms arranged in four rings)
functions:
determine membrane fluidity that changes with temperature therefore allows membrane to function at a wider range of temps
reduces the permeability to hydrophilic molecules and ions (such as sodium, hydrogen)
51
What are the other functions of the specific membrane proteins?
- channel protein (passive transport)
- pump protein (active transport)
- enzymes and carriers (ex. electron carrier, catalysis of reactions)
- receptors, antigens,
- cell-cell recognition
- cell binding sites (for antigen-antibody reaction)
52
What is the basic difference between active and passive membrane transport?
passive doesn't require ATP (along concentration gradient - from high to low)
and active does as it moves against concentration gradient
53
54
55
What are the main types of active transport?
primary (direct) (pump-mediated)- direct use of ATP to mediate transport
secondary (indirect)(carrier-mediated) - coupling the molecule with another moving along an electrochemical gradient
56
What is simple diffusion?
the net movement of molecules from region of high concentration to a region of low concentration, that often in living organism involves a membrane, that will continue until equilibrium, small, non-polar molecules
57
What are the factors affecting diffusion and in what way?
- temperature- higher=diffuse faster
- surface area - larger=diffuse faster
- concentration gradient - higher = diffuse faster
- size of particles- smaller=diffuse faster
58
Define facilitated diffusion
is the passive movement of molecules, that are unable to freely cross the phospholipid bilayer (large and polar), involving a membrane with specific carrier proteins or channel proteins
59
Define the term carrier proteins
integral glycoproteins which bind a solute and undergo a conformational change to translocate the solute across the membrane, they will only bind a specific molecule via an attachment similar to an enzyme-substrate interaction
60
Define channel proteins
integral lipoproteins which contain a pore via which ions may cross from one side of the membrane to the other,
are ion-selective and may be gated to regulate the passage of ions in response to certain stimuli
61
Define the term osmosis
the net movement of water molecules across a semi-permeable membrane from a region of low solute concentration (hypotonic) to a region of high solute concentration (hypertonic) until equilibrium is reached
62
Why is water called the universal solvent?
because it will associate with and dissolve polar or charged molecules (solutes)
63
What is osmolarity?
a measure of solute concentration, as defined by the number of osmoles of solute per litre of solution
64
List and define the types of solutions relating to their osmolarity
hypertonic - (plasmolyzed) greater solute concentration than the cytosol, higher osmolarity -> loses water
hypotonic - lesser solute concentration than cytosol, Lesses concentration of impermeable solutes, lower osmolarity ->gains water
isotonic - equal concertation of impermeable solutes on either side of the membrane, -> no net water flow
65
What are the negative effects of uncontrolled osmosis with regards to cell viability?
- crenation (animal cells) - in hypertonic solutions water will leave the cell causing it to shrivel
- lysis (animal cells) - in hypotonic solutions, water will enter the cell causing it to swell and potentially burst
- plasmolysis(plant cells) - in hypertonic solutions, the cytoplasm will shrink but the cell wall will maintain a structured shape
66
How can the energy needed for active transport be generated?
- direct hydrolysis of ATP (primary)
- indirect coupling transport with another molecule that is moving along its gradient (secondary)
67
Explain in simple how does the active transport via protein pumps work
a specific solute bind to the protein pump on one side of the membrane->hydrolysis of ATP (into ADP+Pi) causes a conformational change in the protein pump->solute molecule is consequently translocated across the membrane and released
68
What are the key steps of ion exchange via the sodium-potassium pump?
1. Three sodium ions bind to intracellular sites on the sodium-potassium pump.
2. A phosphate group is transferred to the pump via the hydrolysis of ATP.
3. The pump undergoes a conformational change, translocating sodium across the membrane.
69
What is the bulk transport and what other name it has?
cytosis
is a type of movement that occurs by the movement of vesicles with matter across the membrane, it allows larger molecules to move and depends on the fluidity of the membrane
70
List the two types of bulk transport and define them and list an example of its presence
exocytosis - large substances exit the cell without crossing the membrane bc vesicles derived from the Golgi fuse with the plasma membrane expelling their contents into the extracellular environment e.g. pancreatic cells producing insulin and secreting it into bloodstream, neurotransmitters released at synapses
endocytosis - large substances enter the cell without crossing the membrane via invagination of the membrane forming a flask-like depression which envelopes the extracellular material that is later sealed off to form an intracellular vesicle (phagocytosis-ingestion of solids, pinocytosis- ingestion of liquids)
71
What is the cell cycle and what does it consist of?
a description of the behaviors of cells as the grow and divide, integrating the growth phase with the divisional phase (interphase & mitosis) consists of interphase(G1+S+G2 and G0)
72
What happens during the specific phases of the interphase?
G1- major cell growth, active cytoplasm, formation of new organelles, biochemical intense activity (transcription, translation)
S - synthesis stage, DNA replication, chromatids
G2- prep for division, proliferation of the organelles, DNA condensation into chromosomes, formation of microtubules
G0- non-growing state in which some (e.g. muscle, nerve cells) stay forever
73
What are cyclins?
cyclins are a group of regulatory proteins that control the progression of the cell cycle by binding (and therefore activating) the CDKs (cyclin dependent kinases) enabling them to act as enzymes
checkpoint is when the CDKs function
74
List the differences between chromatin and chromosome and chromatid
Chromatin:
-DNA is usually loosely packed within the nucleus as unraveled chromatin.
- In this unraveled form, the DNA is accessible to transcriptional machinery and so genetic information can be translated.
- DNA is organized as chromatin in all non-dividing cells and throughout the process of interphase.
Chromosome:
- DNA is temporarily packaged into a tightly wound and condensed chromosome prior to division (via supercoiling).
- In this condensed form, the DNA is able to be easily segregated however is inaccessible to transcriptional machinery.
- DNA is organized as chromosomes during the process of mitosis (condense in prophase, decondense in telophase).
Chromatid:
A chromosome is the condensed form of DNA which is visible during mitosis (via microscopy).
As the DNA is replicated during the S phase of interphase, the chromosome will initially contain two identical DNA strands.
These genetically identical strands are called sister chromatids and are held together by a central region called the centromere.
When these chromatids separate during mitosis, they become independent chromosomes, each made of a single DNA strand.
75
What is mitosis?
the process of nuclear division, whereby duplicated DNA molecules are arranged into two separate nuclei, is proceeded by an interphase and divided into four distinct stages: prophase, metaphase, anaphase, telophase and cytokinesis which occurs concurrently wi8th the final stage of mitosis
76
Describe the process of supercoiling of the chromatin.
DNA wraps around histones (nucleosomes)-> further wrapped into solenoid -> grouping in looped domains -> chromosome.
77
List processes that happen in the prophase
- formation of chromosomes (chromatin fiber becomes tightly coiled)
- disintegration of the nuclear envelope and disappearance of the nucleoli
- formation of the mitotic spindle
- lengthening of the microtubules -> movement of the centrosome towards the opposite poles
78
Define and list the functions of the MTOC
microtubule-organising centre
structure found in eukaryotic cells from which microtubules emerge
functions:
- organization of flagella and cilia
- organization of the mitotic & meiotic spindle apparatus.
79
List processes that happen in the metaphase
movement of chromosomes to the equator of the cell - metaphase plate - in reaction to the microtubule spindle action (depolymerization)
80
List processes that happen in the anaphase
- begins when two sister chromatids are split
- the microtubules contract causing the chromatids to move towards the opposite poles
81
List processes that happen in the telophase
- chromosomes start to elongate to form a chromatin
- nuclei reappears
- spindle apparatus disappears
- nuclear membranes reform around each chromosome set
- cytokinesis occurs
82
Define and describe to process of cytokinesis
is the process of cytoplasmic division whereby the cell splits into two identical daughter cells, is different in plant and animal cells.
Animal Cells inward pinching of the fluid plasma membrane to form cleavage furrows.
- After anaphase, microtubule filaments form a concentric ring around the centre of the cell
- The microfilaments constrict to form a cleavage furrow, which deepens from the periphery towards the centre
- When the furrow meets in the centre, the cell becomes completely pinched off and two cells are formed
Plant Cells forming of a cell plate midway between the two poles
- After anaphase, carbohydrate-rich vesicles form in a row at the centre of the cell (equatorial plane)
- The vesicles fuse together and an early cell plate begins to form within the middle of the cell
- The cell plate extends outwards and fuses with the cell wall, dividing the cell into two distinct daughter cells
83
Describe why animal cytokinesis is centripetal and plant is centrifugal.
- Because animal separation occurs from the outside and moves towards the centre, it is described as centripetal.
- Because plant separation originates in the centre and moves laterally, it is described as centrifugal.
84
List the functions of mitosis
Tissue repair / replacement:
- Damaged or aged cells replaced with identical healthy ones
Organismal growth:
- Multicellular organisms derive new cells via mitosis
Asexual reproduction:
- Vegetative propagation in plants occurs via mitotic division
Development (of embryos):
- Zygotes undergo mitosis and differentiate to become embryos
Mnemonic: TOAD
85
Define what is the mitotic index, list its formula and its function
is a measure of the proliferation status of a cell population that includes the ratio between the number of cells in mitosis in a tissue over the total number of cells
formula:
mitotic index=number of cells in mitosis/total number of cells
function:
important prognostic tool for predicting the response of cancer cells to chemo
86
define what is tumor
abnormal cell growths resulting from uncontrolled cell division and can occur in any tissue or organ.
87
What is the difference between a secondary and primary tumor?
primary occurs at the original site of cancer whereas secondary has spread from the original location.
88
What are mutagens and list their types and why are they classifies as carcinogens?
agents that changes the genetic material of an organism (either acts on the DNA or the replicative machinery)
Mutagens may be physical, chemical or biological in origin:
- Physical – Sources of radiation including X-rays (ionizing), ultraviolet (UV) light and radioactive decay
- Chemical – DNA interacting substances including reactive oxygen species (ROS) and metals (e.g. arsenic)
- Biological – Viruses, certain bacteria and mobile genetic elements (transposons)
Mutagens that lead to the formation of cancer are further classified as carcinogens.
89
Define the term oncogenes, list and describe its two types
a gene that has the potential to cause cancer. Most cancers are caused by mutations to two basic classes of genes – proto-oncogenes and tumor suppressor genes.
- Proto-oncogenes code for proteins that stimulate the cell cycle and promote cell growth and proliferation
- Tumor suppressor genes code for proteins that repress cell cycle progression and promote apoptosis
When a proto-oncogene is mutated or subjected to increased expression it becomes a cancer-causing oncogene.
Tumor suppressor genes are sometimes referred to as anti-oncogenes, as their normal function prevents cancer.
90
Define the term metastasis.
Metastasis is the spread of cancer from one location (primary tumor) to another, forming a secondary tumor.
Secondary tumors are made up of the same type of cell as the primary tumor – this affects the type of treatment required.
E.g. If breast cancer spread to the liver, the patient has secondary breast cancer of the liver (treat with breast cancer drugs)
91
State and describe by what normally should the process of cell mutation be prevented (list the two types)
by the PCD - programmed cell death
apoptosis (necessary) or necrosis (detrimental)
Necrosis is uncontrolled cell death (‘cell homicide’)
- Necrosis is the premature death of a cell, caused by disruption to the cell by injury, toxins or nutritional deprivation.
- The cell loses functional control and there is destabilization of the plasma and organelle membranes.
- This leads to swelling of the cell and organelles due to increased osmotic pressure, and the cell eventually bursts.
- The uncontrolled release of cell contents causes inflammation, potentially damaging surrounding tissue.
Apoptosis is programmed cell death (‘cell suicide’).
- Apoptosis is a controlled event regulated by molecular signals which inhibit or promote this process
- Mitochondrial proteins play an important role in initiating apoptotic processes
- Catabolic reactions are triggered which digest cytoplasmic components, including the cytoskeleton
- The plasma membrane undergoes irregular bulging, or blebbing, and cell contents are repackaged for safe removal
- The cell shrinks and fragments into apoptotic bodies which are subsequently engulfed by neighboring cells
92
What are two types of stem cells and distinguish them
ESC - embryonic stem cells
- coming from 3-5 day old embryos, can become any type of cell
ASC - adult stem cells
- undifferentiated cells residing among differentiated cells of a tissue/ organ
EMBRYONIC STEM CELLS
- easier to obtain than adult stem cells.
- almost unlimited growth potential - much greater than for adult stem cells.
- less chance of genetic damage than with adult stem cells.
- greater capacity to differentiate into different cell types than adult stem cells.
ADULT STEM CELLS
- no embryo needs to be destroyed, which usually happens when embryonic stem cells are obtained.
- the cells are fully compatible with the tissues of the adult, so no rejection problems occur, whereas embryonic tissue is genetically different from the patient receiving the tissue.
- less chance of malignant tumors developing than with embryonic stem cells.
93
What are the categories of stem cells?
totipotent - can differentiate into all cells, produced from the fusion of an egg and sperm cell and the first few divisions of the fertilized egg.
pluripotent - can differentiate into all cells except placenta and chorion, descendants of totipotent.
multipotent - can give rise to a limited number of cell types depending on its tissue of origin.
94
State what and why must occur before meiosis?
during interphase - chromosome replication enables cell to have a copy of each chromosome and increases potential for genetic recombination.
95
Explain what happens in Prophase I
formation of bivalents and tetrads by synapsis, crossing over occurs
96
Define homologous chromosomes
same length, centromeres in the same position, same genes one from mother one from father, different alleles for each gene along chromatids
97
Define crossing-over
process of mixing genetic material between non-sister chromatids when the chromatids intertwine and brake at exactly the same points
98
Define chiasmata
place where non-sister chromatids remain physically connected during crossing-over
99
Distinguish tetrads from bivalents
The connected homologues are known as a bivalent (bi = two chromosomes) or a tetrad (tetra = four chromatids)
100
State what happens in metaphase I
alignment of bivalents along the middle of the cell by spindle fibers, random assortment
101
Define random assortment
homologous chromosomes can line up in two arrangements (maternal left, paternal right or maternal right, paternal left), their orientation is random and not affected by another pair therefore allele on one chromosome has equal chance of being paired with/separated from any allele.
102
Distinguish meiosis I and II
during meiosis 1, chromosomal cross-over occurs at the prophase 1, leading to the genetic recombination whereas no chromosomal cross-over is identified during meiosis 2.
meiosis I is the first cell division of meiosis that produces two haploid cells from a diploid cell while meiosis II is the second cell division that completes the meiosis by producing four haploid cells.
103
Define the term abiogenesis
theory that living cells arose from non-living matter
104
List the stages of abiogenesis
- non-living synthesis of simple organic molecules (sugars and amino acids) and their accumulation in the primitive terrestrial environment
- assembly of these molecules into more complex polymers (prebiotic condensation)
- development of self-replicating molecules e.g. nucleic acids
- formation of photobiont - packaging of them into membranous sacs, so that internal chemistry can develop
105
What is the experimental evidence for the origin of organic molecules?
Miller-Urey experiment
strong electric sparks passed through mixtures of methane, ammonia, hydrogen, water vapor -> repetition with other sources of energy and mixtures -> products in form of amino acids, fatty acids, sugars and nucleotide bases and simple polymers -> wide range of organic compounds could have formed on the pre-biotic earth
106
Define endosymbiosis
theory that explains the origin of eukaryotic cells
early prokaryotes were engulfed by phagocytosis and remained undigested and contributed new functionality (e.g. photosynthesis) and eventually became a mitochondrion and chloroplast.
107
List evidence supporting endosymbiosis
- own genes like prokaryotes (naked and circular)
- 70S ribosomes
- can be produced by division
- susceptible to antibiotics (=> bacterial origins)
- double-membrane
