cell division, cell diversity and cellular organisation Flashcards
what is the cell cycle made up of (brief)
preparation for cell division (INTERPHASE)
cell division (MITOSIS AND MEIOSIS)
parts of the cell cycle (in order)
Gap 1
S
Gap 2
Mitosis/Meiosis
Cytokinesis
what are the parts of interphase?
gap 1
G1/S checkpoint
S phase
gap 2
G2/S checkpoint
what is interphase?
preparation for cell division
describe what takes place during Gap 1 of cell cycle
GROWTH
cell increases in volume
organelle replication
protein synthesis (produce growth factors and enzymes which are sued in DNA replication in S phase)
what does G1/S checkpoint check for?
checks for DNA damage
checks cell is large enough
checks cell has duplicated organelles
a checkpoint during G1 detects DNA damage. what could be the consequences of this?
DNA may be repaired, in which case cell continues to S phase
if it cannot be repaired, it enters resting phase G0 or is destroyed
describe what takes place during S phase of cell cycle
(synthesis) DNA REPLICATES
ensures twice the original DNA content (each daughter cell receives half)
describe what takes place during gap 2 of cell cycle
GROWTH/PREPARATION FOR CELL DIVISION
energy stores increase
cell increases in volume
synthesising key proteins for cell division
what does G2/S checkpoint check for
checks for correct DNA replication
stages of mitosis
prophase
metaphase
anaphase
telophase
what does M checkpoint check for?
(metaphase checkpoint)
spindle assembly checkpoint
checks that spindle fibres are correctly attached to chromosomes
what happens during cytokinesis (brief)
cell divides in 2
cytoplasm divides
why are checkpoints so important?
control cell cycle.
ensure DNA not damaged so that daughter cells produced are genetically identical to parent cell
prevent uncontrolled cell division which could lead to tumours
DNA in daughter cells contain no errors
when is a cell in the G0 phase?
- cell may leave cell cycle and enter G0 if it fails one of the checkpoints -> repaired and re-enters cell cycle OR destroyed by apoptosis
- cell may leave cell cycle if it is going to become specialised e.g. stem cell differentiates into RBC/ neurone
is interphase a resting phase?
why?
NO IT IS NOT A RESTING PHASE
in G, S, G2: significant metabolic activity is taking place
e.g. protein synthesis, DNA replication, aerobic respiration
which types of cells could be considered to be in a resting phase
cells are resting if they are not actively dividing
BUT
specialised cells e.g. neurones, liver cells carry out significant metabolic activity
whats the significance of mitosis in life cycles?
growth, development and tissue repair
clonal expansion of lymphocytes
production of new stem cells
development of body plan (balance between mitosis and apoptosis)
asexual reproduction (one parent cell divides to from 2 genetically identical daughter cells)
what takes place during prophase
chromatin condenses (chromsones become visible)
nuclear envelope breaks down
nucleolus disappears
centrioles migrate to opposite poles of the cell
spindle fibres start to form
what takes place during metaphase
spindle fibres attach to centromeres of each pair of sister chromatids
once attached, chromosomes line up along equator/metaphase plate
leads to metaphase checkpoint, which checks spindle assembly
what takes place during anaphase
spindle fibres shorten and pull sister chromatids apart and separate them to opposite poles (REQUIRES ATP)
centromere has divided
what takes place during telophase
full set of chromosomes at each pole of the cell
nuclear membrane forms around each set of chromosomes and a nucleolus reappears
chromosomes uncoil, reforming chromatin
is cytokinesis a stage of mitosis?
NO
it is distinct and separate
describe cytokinesis in an animal cell
cleavage furrow forms down centre of the cell
actin microfilaments contract (ATP required) and separate the 2 cells by pinching the plasma membrane together -> 2x genetically identical daughter cells
describe cytokinesis in a plant cell
vesicles containing cellulose are deposited at the cell plate
cellulose molecules hydrogen bond together, forming microfibrils then macrofibrils
cel splits into 2x genetically identical daughter cells
role of cell membrane in cytokinesis
cell membrane pulls inwards (cleaves) to separate cytoplasm into 2
plants lack centrioles. what does this indicate about the role of centrioles in mitosis?
spindle fibres still form in plant cells BUT they are not produced by centrioles
therefore they are not essential in all cells
homologous pair of chromosomes characteristics
a pair of matching chromosomes
1 maternal and 1 paternal
similar size
genes are located in similar positions (loci)
number of chromosomes/chromatids in human cell prior to and after S phase and then after mitosis/cytokinesis
46 chromosomes/ 46 chromatids prior to S phase
46 chromosomes/ 92 chromatids after S phase
each daughter cell contains 46 chromosomes/ 46 chromatids
what is a stem cell?
an unspecialised cell
has the potential to become a specialised cell (leave the cell cycle)
self-renewing through mitosis
where can scientists obtain stem cells?
bone marrow
embryos (donated from IVF)
tissues (e.g. skin, brain, blood, muscle, guts)
neural stem cells from the brain can differentiate into which types of cell?
the 3 types of cell which exist in the brain
how can stem cells be used in the treatment of burns?
sample of skin from unburned area taken
stem cells undergo mitosis and a layer of skin cells is grown/cultured
layer is transplanted onto patient
(can only form outer layer of skin: no sweat glands e.t.c.)
how can stem cells be cultured in a laboratory? i.e. which substances are required in the medium?
glucose
oxygen
amino acids
growth hormones
vague roles of stem cells in our bodies?
repairing wounds
replacing old blood cells
4 types of stem cells
totipotent
pluripotent
multipotent
induced pluripotent (iPSCs)
examples of embryonic stem cells
totipotent
pluripotent
totipotent stem cells:
extracted from?
can differentiate into?/potency?
ability?
extracted from first 1-32 cells of an embryo
can differentiate into ALL cell types INCLUDING extra-embryonic cells e.g. placenta and umbilical cord
therefore has ability to form whole living organisms
pluripotent stem cells:
extracted from?
can differentiate into?
extracted from first 64-256 cells of embryo
can differentiate into ALL cell types EXCEPT extra-embryonic cells e.g. placenta and umbilical cord
multipotent stem cells:
what kind of stem cell?
extracted from?
can differentiate into?
somatic/adult stem cells
extracted from bone marrow (HAEMATOPOETIC stem cells)
can differentiate into many cell types, including lymphocytes, phagocytes, erythrocytes
induced pluripotent stem cells:
what are they?
potential in what?
reprogram differentiated cells to become embryonic/pluripotent stem cells
potential in areas like regenerative medicine
function of bone marrow stem cells
can differentiate into different types of blood cells e.g. neutrophils and RBCs, which are short-lived cells so must be replaced
what are meristems?
tissues found in plants which contain stem cells
all other cells in plant are derived from meristems by cell differentiation
meristematic tissue is found in plant vascular bundle. what is the purpose of this tissue?
found between xylem and phloem (in cambium)
can differentiate into cells that form xylem (elongated, lined with lignin) or those that form phloem (sieve tubes or companion cells)
3 potential uses of stem cells in medicine
repair of damaged tissues e.g treat burns, repair heart tissue
treat neurological conditions e.g. Alzheimers or Parkinson’s by replacing damaged nerve tissue with transplanted neurones generated from donor & patient derived iPSCs
research into developmental biology. since they can all divide and differentiate into almost any cell type, stem cells can be used to research into the development of multicellular organisms and look at potential cures for problems and how to increase longevity.
7 examples of specialised cells
erythrocytes
neutrophils
squamous and ciliated epithelial cells
palisade cells
root hair cells
sperm cells
guard cells
features of erythrocytes that better adapt them for their function
biconcave shape
thin walls
flexible shape
presence of haemoglobin
no nucleus
erythrocytes function?
carry oxygen from the lungs to the rest of the body
transportation of gases and nutrients through body
how does biconcave shape of erythrocytes better adapt them for their function?
higher surface area than a flat surface, so an increased ability to absorb oxygen
increased surface area to volume ratio, which allows diffusion to happen quickly and efficiently
how do thin walls of erythrocytes better adapt them for their function?
allows oxygen to diffuse through quickly due to decreased diffusion distance
flexible so can squeeze through narrow capillaries
how does presence of haemoglobin in erythrocytes better adapt them for their function?
oxygen combines reversibly with haemoglobin to for oxyhaemoglobin, so increases carrying capacity of RBC
how does lack of nucleus in erythrocytes better adapt them for their function?
more room for haemoglobin in the cell
what type of stem cell differentiates to form an erythrocyte?
where are these stem cells found?
hematopoietic stem cells (HSCs)
found in bone marrow
what are neutrophils an example of
a phagocyte (white blood cell)
why do neutrophils have a lobed nucleus?
lobular arrangement makes the nucleus easier to deform and hence help the neutrophils pass through small gaps in the endothelium and extracellular metric more easily to get to the site of infection
why are neutrophils full of lysosomes?
they must digest more material than most other types of cells when fighting bacteria, viruses and other pathogens
how does a neutrophil digest an engulfed pathogen
pathogen= within phagocytic vacuole
neutrophil secretes digestive enzymes into the vacuole (enzymes are released from lysosomes which fuse with the vacuole)
these digestive enzymes destroy the pathogen
how would you distinguish a lymphocyte form a neutrophil using a microscopic image?
neutrophil has multi lobed nucleus
lymphocyte has large round nucleus
structure of cilia?
protrusions from the cell, surrounded by the cell surface membrane
9+2 microtubule arrangement
formed from centrioles
purpose of cilia in airways?
propel a liquid layer of mucus that covers the airways
move microbes/debris up and out of thew airways by wafting the mucus it is stuck to
avoids infection
how is mucus produced?
major macromolecular components of mucus, the mucin glycoproteins, are secreted by surface epithelial goblet cells
exocytosis of secreted mucins= final step in intracellular processing
released from goblet cells into airway lumen to interact with water and ions to form mucus
how are squamous epithelial cells adapted for their function
consists of a single layer of flattened cells on a basement membrane
forms a thin cross-section with decreases distance that substances have to move to pass through (decreased diffusion pathway)
permeable for easy diffusion of gases
structure of flagellum
9+2 microtubule arrangement
composed of 20 protein components
divided into 3 substructures: filament (in helix), hook and basal body
parts of a sperm cell?
head (acrosome and nucleus), neck, middle piece (mitochondrion), plasma membrane, tail(flagellum)
role of mitochondria in a sperm cell
site of aerobic respiration
supply energy as ATP to the sperm cell
necessary to provide tail (undulipodium) with the energy supply that is needed to allow the sperm cell to swim towards the egg
how many chromosomes are there in the nucleus of a sperm cell?
why is there variation in the nuclei of different sperm cells?
23 chromosomes (gamete)
meiosis produces haploid nuclei, genetically different from each other and parent cell
new combinations of alleles in sperm cells
why are acrosomes (full of digestive enzymes) important for sperm cells in fertilisation
enzymes break down outer membrane/ protective layer of ovum, allowing sperm to enter and its haploid nucleus fuse w/ haploid nucleus of ovum
purpose of keratin in sperm cell flagella
provides elasticity and structural integrity to cell
why and how do palisade mesophyll cells move chloroplasts around ?
migrate in response to different light intensities ( escape from strong light to avoid photodamage, gather in illuminated sea under weak light to maximise light absorption and photosynthesis rates)
move along cytoskeleton threads (chloroplast actin filaments) and motor proteins
why do root hair cells have many mitochondria and an extensive RER?
mitochondria: site of aerobic respiration. produces energy as ATP for AT of mineral ions
RER: large roles in protein synthesis, so synthesis carrier proteins used in AT
how do stomata open? step by step
light energy= used to produce ATP
used in AT of K+ form surrounding epidermal cells into guard cells, lowering water potential of guard cells
water enters guard cells by osmosis from neighbouring epidermal cells
guard cells swell, but at the tips of the cells the cellulose cell wall is more flexible and is more rigid where it is thicker
tips bulge, guard cells swell
gaps between cells (stoma) enlarge
CLOSE WHEN GCs LOSE WATER AND SHRINK
what are gametes formed by?
meiosis
number and nature of daughter cells produced in mitosis and meiosis
MITOSIS: 2 genetically identical daughter cells
MEOSIS: 4 genetically unique daughter cells
what is meiosis known as?
reduction division
number of divisions in mitosis and meiosis
MITOSIS: nucleus divides once
MEIOSIS: nucleus divides twice
stages of meiosis I
prophase I
crossing over
metaphase I
independent assortment
anaphase I
telophase I
prophase I in meiosis
chromatin condenses and chromosomes become visible
nuclear envelope breaks down and nucleolus disappears
spindle fibres start to form
crossing over: what phase and description
variation in prophase I
non-sister chromatids within the same homologous pair exchange short sections of DNA
use of crossing over?
forms new combinations of alleles
metaphase I in meiosis
each homologous pair lines up along the equator
spindle fibres attach to the centromere
independent assortment: what stage and description
variation in metaphase I
orientation of each homologous pair along the equator is random
use of independent assortment
more possible combinations of alleles in daughter cells
anaphase I in meiosis description
spindle fibres shorten and separate each member of a homologous pair to opposite poles
centromere remains intact
telophase I in meiosis description
e.g. in a human cell: 23 unpaired chromosomes at each pole
nuclear envelope reforms and nucleolus reappears
chromosomes relax
cytokinesis occurs afterwards
number of cells, chromosomes and chromatids before and after meiosis I
BEFORE: 1 parent cell, 46 chromosomes (DIPLOID), 92 chromatids
AFTER: 2 daughter cells, 23 chromosomes each (HAPLOID), 46 chromatids eacg
what happens prior to meiosis II?
short cell cycle without DNA replication
stages of meiosis II
prophase II
metaphase II
independent assortment
anaphase II
telophase II
prophase II meiosis description
chromatin condenses and chromosomes become visible
nuclear envelope breaks down
nucleolus disappears
spindle fibres start to form
metaphase II meiosis description
chromosomes line up along equator
spindle fibres attach to centromeres
independent assortment stage and description
variation in metaphase II
random orientation of chromosomes along the equator which determines which daughter cell each chromatid is separated to
use of independent assortment
produces new combinations of alleles in daughter cells
anaphase II meiosis description
spindle fibres shorten
centromeres divide
sister chromatids pulled to opposite poles
telophase II meiosis description
nuclear membrane forms around each set of chromatids at each pole
nucleolus reappears
chromatids relax to form chromatin
cytokinesis occurs afterwards
number of cells, chromosomes and chromatids after meiosis II
4 daughter cells
23 chromosomes
23 chromatids
how does independent assortment in metaphase I produce variation?
each member of a homologous pair could be separated to a different cell
how does independent assortment in metaphase II produce variation?
each sister chromatid could be separated to a different cell
cell definition
basic structural and functional unit of living organisms
tissue defintion
group of differentiated cells with a specific function
organ definition
collection of tissues working together to perform a particular function
organ system defintion
made up of a number of organs working together to carry out major function
examples of tissues
squamous epithelium
ciliated epithelium
cartilage
muscle
xylem
phloem
function of squamous epithelium
forms linings
allows rapid diffusion
ciliated epithelium function
co-ordinated movement of cilia allows movement of particles
cartilage function
connective tissue, gives strength and protection to structures
muscle function
allows movement of body (bones)
xylem function
transport of water and minerals up a plant
strength and support
phloem function
transport of organic nutrients up and down plants
differences between meiosis and mitosis
mitosis = 2 genetically identical diploid daughter cells
meiosis= 4 genetically unique haploid daughter cells
mitosis=1 division
meiosis= 2 divisions
mitosis= used for growth, repair and asexual reproduction
meiosis= used to produce gametes for sexual reproduction
centromere function
hold together sister chromatids at centre to form chromosome
describe ways in which genetic variation is produced, including role of nuclear division
independent assortment of chromosomes in metaphase I and of chromatids in metaphase II. homologous chromosomes have different alleles so therefore this increases the number of allele combinations
crossing over in prophase I means chromatids have different allele combinations. amount of variation depends on distance between chiasmata
mutation= change in nucleotide sequence. DNA checks did not recognise this damage. this leads to a difference in protein synthesised
non-disjunction= homologous chromosomes not separating in metaphase I so one more/less chromosome present.
random fusion of gametes. gametes are not genetically identical so there is a large number of allele combinations
what do all blood cells originate from?
multipotent stem cells in bone marrow
why are root tips warmed in hydrochloric acid when preparing a root tip squash
to break the links between cellulose cell wall in plant cells
so stain can penetrate the cells and bind to chromosomes
which stain would we use to stain chromosomes in a root tip squash?
toluidine blue
or acetic orcein
3 types of muscle tissue and where they are found
skeletal: bicep/tricep
smooth: digestive tract/blood vessels
cardiac: heart walls
4 features of meristematic cells that means they can differentiate easily
thin
very little cellulose
no chloroplasts or large vacuole
divide by mitosis
true or false: neutrophils undergo mutation during differentiation
false
true or false: erythrocytes develop large numbers of ribosomes early in their differentiation
true
true or false: the majority of organelles in red blood cells are broken down by hydrolysis
true
