Chapter 6 - Cell Division Flashcards
What are the main phases of the cell cycle?
Interphase
Mitotic phase
What is interphase?
Cell spends most of the time in this phase
Not actively dividing
Preparing for cell division
What are the three stages of interphase and what happens in them?
G1 - first growth phase, organelles replicate and cell increases in size
S - synthesis phase, DNA is replicated in the nucleus
G2 - second growth phase, cell continues to increase in size, energy stores are increased and duplicated DNA is checked for errors
What is the mitotic phase?
Period of cell division
Mitosis - nucleus divides
Cytokinesis - cytoplasm divides and two cells are produced
What is G0 and why does it happen?
When cell leaves the cell cycle - temporarily or permanently
Differentiation - specialises then is no longer able to divide
DNA of cell is damaged so can longer divide
Diseases such as arthritis or cancer
How is the cell cycle controlled?
Checkpoints - control mechanisms of the cell cycle, monitor and confirm that processes have been successfully completed before moving onto the next stage
What happens that the G1 checkpoint?
End of G1 phase
Checks for cell size, nutrients, growth factors and DNA damage
If it isn’t completed it will enter G0
What happens at G2 checkpoint?
End of G2 phase
Checks for cell size, DNA replication and DNA damage
If completed the cell initiates the process for mitosis
What happens at the spindle assembly checkpoint?
All chromosomes should be attached to spindles and have aligned during metaphase
Mitosis cannot proceed unless it is complete
What is mitosis?
Process of the nucleus splitting to produce 2 genetically identical nuclei in order to produce two genetically identical daughter cells in cytokinesis
What are the four stages of mitosis?
Prophase
Metaphase
Anaphase
Telophase
What is the process of prophase?
(mitosis)
Chromatin fibres coil and condense
Nucleolus disappears
Nuclear membrane breaks down
Centrioles migrate to opposite poles
Spindle fibres attach to centromeres and start moving chromosomes to the center
Nuclear envelope disappears
What is the process of metaphase?
(mitosis)
Chromosomes are pulled by the spindle fibres to form a plane in the center of the cell called the metaphase plate
What is the process of anaphase?
(mitosis)
Centromeres divide
Chromatids are separated and pulled to opposite poles by the shortening of spindle fibres
What is the process of telophase?
(mitosis)
Chromatids reach the poles (and are now called chromosomes)
Nuclear envelope reforms around the two new sets of chromosomes
Chromosomes uncoil and nucleolus is formed
What is the process of cytokinesis in animal cells?
Forms a cleavage furrow around the middle of the cell
The cell surface membrane is pulled inwards by the cytoskeleton until it is close enough to form around the middle forming two cells
What is the process of cytokinesis in plant cells?
No cleavage furrow forms due to it having a cell wall
Vesicles from the golgi apparatus begin to assemble in the same place as the metaphase plate was formed and the vesicles fuse to each other and the cell surface membrane dividing the cell into two
New sections of the cell wall form along the new membrane
What is a diploid cell?
A cell with two chromosomes of each type
One from the mother one from the father
What is a haploid cell?
A cell with one chromosome of each type
e.g. gamete
What are homologous chromosomes?
Chromosomes with the same genes at the same loci
They are not the same chromosomes as they have one from each parent
What is an allele?
Different versions of the same gene (gene variants)
What are the two phases of meiosis?
Meiosis 1
Meiosis 2
What happens in meiosis 1?
Pairs of homologous chromosomes are separated
Each cell will only contain one full set of genes instead of two so the cells are haploid
What happens in meiosis 2?
Pairs of chromatids are separated
Produces four haploid daughter cells
What is the process of prophase 1?
(meiosis)
Chromosomes condense
Nuclear envelope disintegrates
Nucleolus disappears
Spindle formation begins
Homologous chromosomes pair up forming bivalents
Chromosomes do crossing over
What is the process of metaphase 1?
(meiosis)
Same as metaphase in mitosis but instead homologous pairs of chromosomes assemble along the metaphase plate
Orientation of each homologous pairs are random
What is the process of anaphase 1?
(meiosis)
Bivalents are pulled to opposite sides and chromosomes stay joined together
Chiasmata - point at which chromatids break and rejoin during crossing over
Exchange forms recombinant chromatids which leads to genetic variation
What is the process of telophase 1?
(meiosis)
Same as mitosis telophase
Chromosomes assemble at each pole and the nuclear membrane reforms
Chromosomes uncoil
Cell undergoes cytokinesis and divides into two haploid cells
What is the process of prophase 2?
(meiosis)
Chromosomes condense
Nuclear envelope breaks down
Spindle formation starts again
What is the process of metaphase 2?
(meiosis)
Individual chromosomes assemble on the metaphase plate
What is the process of anaphase 2?
(meiosis)
Chromatids of a chromosome are pulled apart to opposite poles after division of centromeres
What is the process of telophase 2?
(meiosis)
Chromatids assemble at the poles
Chromosomes uncoil
Nuclear envelope reforms
Nucleolus becomes visible
Cytokinesis results in four haploid daughter cells
What is meiosis?
Production of gametes for sexual reproduction
Produces variation
What is the process of crossing over?
Swapping of genes at a point called the chiasma
This creates variation
Only happens in prophase 1
What is independent segregation of chromosomes?
Chromosomes align on the metaphase plate randomly and one from each pair goes into a daughter cell
In metaphase 1 and 2
How can genetic variation be created?
Independent segregation of chromosomes
Crossing over
Mutations
Random sperm reaching random egg
What is a cell?
Smallest unit of a living thing
Differentiated meaning it is specialised to carry out a specific function
What is a tissue?
A collection of the same differentiated cells that have a specialised function
What is an organ?
A collection of different tissues adapted to perform a specific function
What is an organ system?
Composed of a number of organs working together to carry out a major function in the organism
What is the levels of organisation in multicellular organisms?
(smallest to biggest)
Cells
Tissues
Organs
Organ systems
Organism
What is an erythrocyte?
Animal cell
Red blood cell
Flattened biconcave shape - Increased surface area to volume ratio
No nucleus - space for haemoglobin
Transport Oxygen around body
Flexible - to fit through narrow capillaries
What is a neutrophilis?
Animal cell
White blood cell
Multi-lobed nucleus - easier to squeeze through gaps to get to the site of infection
Granular cytoplasm - contains lysosomes with enzymes to attack pathogens
What is a sperm cell?
Animal cell
Gamete
Delivers genetic information to the ovum (egg cell)
Flagellum for movement
Lots of mitochondria for energy to swim to the egg
Acrosome on the head contains digestive enzymes to break protective layer around the ovum
What are palisade cells?
Plant cell
Present in mesophyll
Lots of chloroplasts to absorb light, can move to absorb more light
Thin cell walls - increases diffusion rate of carbon dioxide
Large vacuole - maintain turgor pressure
What are root hair cells?
Plant cell
Present at growing tips of roots
Hairs increase surface area of cell which maximises uptake of water
What are guard cells?
Plant cell
Pairs of guard cells form stomata - necessary for carbon dioxide to enter plants for photosynthesis
When guard cells lose water they become less swollen, they change shape and the stomata closes
What is the squamous epithelium?
Animal tissue
Specialised squamous epithelium cells
Very thin - one cell thick
Lining of the lungs
What is the ciliated epithelium?
Animal tissue
Cilia on the surface
Lines trachea
Contains goblet cells - secrete mucus
What is cartilage?
Animal tissue
Connective tissue
Fibres of elastin and collagen
Chondrocyte cells embedded in the extracellular matrix
What is muscle?
Animal tissue
Can contract
Has fibres
Contain myofibrils
Contain contractile proteins
What is the epidermis?
Plant tissue
Closely packed cells on plants
Waxy and waterproof
Has stomata
What is the xylem tissue?
Plant tissue
Vascular tissue
Transports water and minerals
Made up of dead cells
Strengthened by lignin
What is the phloem tissue?
Vascular tissue
Transport of organic nutrients such as sugar
Columns of sieve tubes - separated by sieve plates
What are stem cells?
Undifferentiated cells that undergo cell division again and again as necessary
Needed for growth and development
Become specialised by differentiation
Once a stem cell becomes differentiated it can no longer undergo cell division
What is potency?
A cells ability to differentiate into different types of cell
What is a totipotent stem cell?
Can differentiate into any type of cell
Only found in zygote in its first 8 or 16 cells which can form the whole organism
What is a pluripotent stem cell?
Form all kinds of tissues but not whole organisms
e.g. early embryos (embryonic stem cells)
What is a multipotent stem cell?
Can differentiate into a limited range of cells
e.g. hematopoietic stem cells in the bone marrow can differentiate into various blood cells
Why is it important for erythrocytes to be renewed so often?
No nucleus or membrane bound organelles so have a lifespan of 120 days
Why is it important for neutrophils to be renewed so often?
Important role in the immune system
Have a lifespan of 6 hours
Can only engulf a few pathogens before dying
Why is it important for multicellular organisms to have specialised cell?
To take on different roles in tissues and organs
To meet the high metabolic demands
Where can animal stem cells be sourced from?
Embryonic - can be extracted from a zygote
Adult - bone marrow or umbilical cord
Where can plant stem cells be sourced from?
Meristems - found at root tips and shoots or in between the phloem and xylem
What can stem cells be used for?
Heart disease
Type 1 diabetes
Parkinson’s disease
Alzheimer’s disease
Macular degeneration (blindness)
Birth defects
Spinal injuries
Treatment of burns
Drug trials
What are the ethical issues around using embryonic stem cells?
Removal of stem cells from embryos often results in destruction
Religious and moral objections - belief that life begins at conception
Lack of consensus - when does the baby have right to consent to this treatment and who does the genetic material used for research belong to
