chapter 6 - cell division Flashcards
what is the common misconception about chromosomes during DNA replication
when chromosomes multiply, cells are believed to have 92 chromosomes
however, when they multiply, the individual units are chromatids, they become chromosomes when two chromatids are bound via a centromere (in the centre) forming one chromosome.
meaning that 46 chromosomes –> 92 chromatids = 46 chromosomes
what are the four phases mitosis and describe them
- prophase - chromatin forms chromosomes (condense) , centrioles move to opposite ends of the cell, spindle fibres start to form
- metaphase - chromosomes line up in the middle of the cell (metaphase plate), chromosomes attach to the spindle by their centromere, metaphase/ spindle checkpoint
- anaphase - centromeres divide, sister chromatids separate, spindles contract pulling chromatids to opposite ends of the cell (centromeres first) creating a v shape with the chromatid
- telophase - chromatids reach opposite ends of the cell (now chromosomes) two nuclear envelopes form and two nuclei are produced
what are the 3 main stages of the cell cycle and describe them
interphase - synthesis of proteins and replication of organelles
mitosis - nuclear division
cytokinesis - cell division
what are the 3 stages of interphase
G1 - biosynthesis = proteins synthesise and organelles replicate, G1 checkpoint for errors
S - synthesis - DNA replication
G2 - continued cell growth - proteins needed for cell division made, DNA checked for errors, damage and ensure complete replication
what forms chromatin
DNA + histones (ball shaped proteins)
DNA wrapped around a histone
describe the stages of mitosis
prophase - chromosomes condense, centrioles start to move to opposite ends of the cell, spindle fibres form, nuclear envelope starts to break down
metaphase - chromosomes line up along middle of the cell, chromosomes attached to spindle via their centromere, metaphase checkpoint
anaphase - centromeres divide, separating sister chromatids, spindles contract pulling chromatids to opposite ends of the cell - centromere first
telophase - chromatids reach opposite ends of the cell, two nuclear envelopes form, two nuclei
what cells in plants and animals undergo mitosis
plants - only meristem (cambium, root and shoot tips) cells
animals - most cells
what are the differences between mitosis in animal and plant cells
plant - no centrioles
animal - centrioles (protein)
plant - cytokinesis starts with formation of cell plate
animal - cytokinesis starts from outside (nipping in of cell membrane)
what occurs in cytokinesis?
two new cell surface membranes form
two new identical daughter cells form
completes cell cycle
in multicellular organisms, mitosis makes new cells for…?
growth of an organism
repair of tissues/ replacement of cells
what is the bacterium alternative to the cell cycle?
binary fission
how fast is the cell cycle in:
1. humans
2. onion root tip
3. yeast cell
- 23 hours
- 20 minutes
- 4 hours
list the four stages of mitosis
Prophase - preparation
Metaphase - middle
Anaphase - apart
Telophase - two
why does DNA have to supercoil before mitosis
so it can be easily segregated
what are somatic cells?
any cells that are not gametes (sperm or egg cells)
what are diploid and haploid cells
diploid cells - contains a complete set of chromosomes in its nucleus
haploid cells - contain a single set of chromosomes (mainly egg and sperm cells)
what is the common misconception about cells that undergo meiosis?
misconception is that they are haploid cells.
cells that undergo meiosis are diploid cells that produce genetically different daughter haploid cells
what are homologous chromosomes
two chromosomes that are similar shapes and sizes, code for the same gene but may express different characteristics
what are alleles
different forms/ versions of the same gene
hence, genetic material might not be identical
what two ways can genetic variation occur in meiosis
- crossing over of chromatids, two homologous double-banded chromosomes, their chromatids cross over - new combination of alleles. recombination
- independent assortment of chromosomes - in meiosis 1, the chromosomes are sorted randomly into two daughter cells, can cause variation as homologous pairs are not genetically identical
outline the stages of meiosis
interphase - diploid cell’s DNA replicates to produce double-armed chromosomes
meiosis 1
prophase 1 - chromosomes condense, homologous chromosomes pair up and chromatids cross over (recombination)
metaphase 1 - homologous pairs line up across centre, attach to spindle by their centromeres
anaphase 1 - spindles contract CHROMOSOMES are pulled to opposite ends of the cell
telophase 1 - nuclear envelope forms, 2 unidentical haploid cells produced.
meiosis 2 - 2 daughter cells undergo telophase 2, metaphase 2, anaphase 2 - CHROMATIDS pulled to opposite ends of the cell, and telophase 2, forming 4 new genetically different daughter cells
what is the difference between prophase 1 and prophase 2 in meiosis
prophase 2 - no homologous chromosomes pairing because pairs have already been split by the end of meiosis 1,
no cross-over of chromatids as variation has already occurred.
what is the difference between anaphase 1 and anaphase 2 in meiosis
anaphase 1 - chromosomes are pulled to opposite ends of the cell to their homologous pair
anaphase 2 - chromatids are pulled to opposite ends of the cell to their sister chromatid
what are the 4 main differences of mitosis and meiosis
mitosis = 2 cells produced
meiosis = 4 cells produced
mitosis = one division
meiosis = two divisions
mitosis = diploid cells produced (2n)
meiosis = haploid cells produced (n)
mitosis = genetically identical daughter cells
meiosis = genetically different daughter cells
What are the 3 main reasons for mitosis?
Replace damaged cells
Growth of organisms
Asexual reproduction
Where are meristematic tissues found in plants and what is their function
Found in the tips of roots and shoots, in between the xylem and phloem
Make unspecialised cells that have the potential to specialise into any type of cell
what would be observed in a cell, in which a genetic mutation was stopped at the metaphase checkpoint
some cells would contain the incorrect number of chromosomes
if cells have been replicated, despite containing damaged DNA, which checkpoint hasn’t worked
G1 checkpoint - should be stopped from entering the S phase
why would it be inappropriate to stain red blood cells with fluorescent dye
red blood cells do not contain DNA
why would a cell spend all of its time in the G1 phase
does not undergo mitosis, specialised cell
what observations would lead to the conclusion that a cell stopped dividing at the G2 checkpoint
larger number of (named) organelles
larger nucleus/ more DNA
no visible chromosomes
apart from growth and repair of tissues, what are the other roles of mitosis in multicellular organisms?
asexual reproduction
producing new stem cells
development of body plan
what are the benefits of asexual reproduction
genetically identical offspring
faster
finding mates require time/ energy
large numbers of offspring produced
all offspring will find conditions favourable/ have same adaptations
what are the advantages of using stem cells from umbilical chord blood to bone marrow
The cells in cord blood are less mature
The cells in cord blood are less likely to cause graft-versus-host disease
It’s simpler and safer to donate cord blood than bone marrow, which is a much more involved process since bone marrow donors have to be anaesthetised and are at risk of infection
Retrieving frozen cord blood is quicker since bone marrow is taken from donors as needed meaning collecting it can take much longer
how are sperm cells specialised to carry out their function
flagellum - tail - rotates allows for movement
the head contains the genetic material for fertilisation in a haploid nucleus.
acrosome in the head contains digestive enzymes to penetrate the egg
middle filled with mitochondria to release energy needed to swim
how are erythrocytes specialised
have a flattened biconcave disc shape - increases SA to V ratio
flexible - squeeze through narrow capillaries
no nucleus and no ribosomes (organelles associated with protein synthesis) - makes more room for haemoglobin
how are neutrophils specialised
contain a characteristic multi-lobed nucleus which makes it easier for them to squeeze through small gaps
contains many lysosomes - with digestive enzymes
flexible - phagocytosis
how are palisade cells specialised
contain lots of chloroplasts - maximum light absorption for photosynthesis
large vacuole - maintain turgor pressure
thin cell walls - short diffusion distance
tightly packed cells - increased surface area
how are root hair cells specialised
root hairs - increase surface area to volume ratio - maximise uptake of water and minerals
thin cellulose cell wall - short diffusion distance
how are guard cells specialised
when water lost - change shape and stoma closes to prevent further water loss. cell wall thicker on one side so cell does not change shape symmetrically
what are the four main categories of tissues in animals
nervous tissue: adapted to support the transmission of electrical impulses
epithelial tissue: adapted to cover body surfaces, internal and external
muscle tissue: adapted to contract
connective tissue: adapted to either hold tissues together or as a transport medium
what are stem cells
undifferentiated cells that are not adapted to any particular function but have the potential to differentiate into a specialised cell
define potency of a stem cell
the cells ability to differentiate into different types of cells
the greater number of cell types it can differentiate into, the greater its potency
define totipotent
what cells are totipotent
stem cells that can differentiate into any type of cell and are destined to produce a whole organism
eg. fertilised egg cells
define pluripotent
what cells are pluripotent
stem cells can form all tissue types but not whole organisms
present in early embryos
define multipotent
which cells are multipotent
stem cells that can only form a range of cells within a certain type of tissue
haematopoetic cells in bone marrow are multipotent as they give rise to the various types of blood cell
where do all blood cells derive from?
stem cells in the bone marrow
what are the life spans of red and white blood cells and why?
red = 120 days - due to lack of nucleus and organelles
white = 6 hours - undergo spontaneous apoptosis so they don’t damage tissue
what are the sources of animal stem cells
embryonic - present at very early stage of embryo development and are totipotent, remain as a pluripotent blastocyst until birth
tissue (adult) - found in areas like bone marrow, and umbilical chord. (umbilical advantage = invasive surgery not needed) multipotent
can also be stored/ frozen
what are the sources of plant stem cells
present in the meristematic tissue (meristem), found in tips of roots and shoots.
meristematic tissue located between the phloem and xylem, called the vascular cambium
the vascular tissue can then grow as the plant grows
plant stem cells are always pluripotent
what are some of the uses of stem cells
transplants to help treat diseases such as:
heart disease, Alzheimer’s, muscular degeneration and birth defects
also:
produce skin grafts for treatments of burns
drug trials - potential new drugs can be tested on cultures of stem cells before humans and animals
developmental biology - study of changes that occur as multicellular organisms grow and develop from a single cell
what are some of the issues surrounding ethics of using stem cells
embryonic - the removal of stem cells from embryos normally results in the destruction of the embryos
lack of consensus as to when the embryo itself has rights and who owns the genetic material
name the type of asexual reproduction in yeast
budding
outline the process of asexual reproduction in yeast
mitosis,
swelling/ bulge in surface of cell,
nucleus moves into bulge/bud,
bulge/ bud breaks off/ pinches off,
uneven distribution of cytoplasm
describe how cells are organised in a multicellular organism
cells differentiate/ specialise
groups of specialised cells form tissues
groups of tissues form organs
groups of organs form organ systems
all interact/ work together
what is meant by homologous pair of chromosomes
- one maternal and one paternal
- carry same genes
- carry same / different alleles
- centromere in same position
- usually similar length
- same banding pattern
- pair up in meiosis/ form bivalent
where are squamous cells found and what is their function
act as a surface or short diffusion pathway
found in alveoli, cheek lining and blood vessels
what is the function of ciliated cells and where are they found
move mucus/ or secrete mucus (removal of bacteria or fungi via mucus)
found in bronchioles, bronchi, trachea and airways
where in a plant are meristematic tissues found
just behind the apex of a root or tip of a shoot,
cambium/ pericycle/ vascular bundle,
bud
why might cells under investigation of stages of the cell cycle need to be stained
so chromosomes/ chromatin/ nucleus can be seen/ visible
distinguish between the different stages of the cell cycle
staining provides contrast between cell structures
because different structures take up different amounts of stain
What stages of meiosis does independent assortment occur
How does this differ in the different stages
Metaphase 1 - independent assortment of chromosomes
Metaphase 2 - independent assortment of chromatids
What is an apical meristem
A plant tissue found at the tip of shoots and roots
Why do guard cells have inner and outer walls with different thicknesses
The thicker inner wall stays rigid whilst the outer wall bends, opening the stomata
How can you tell if a cell is a diploid 6 chromosome cell or a haploid 6 chromosome cell
The haploid will not have homologous chromosomes - genetically different
