The developing Cell Flashcards
Cell cycle
Cell growth, maturity and division
This is the process that all somatic cells in multicellular organisms use to grow and divide
Cell cycle 3 stages
interphase, mitosis, cytokenesis
Interphase
not part of mitosis
Growth 1- Cells grow in size & mass, organelles replicated, inc protein synthesis *(chloroplasts & mitochondria not replicated)
Synthesis- DNA replication using SCR
Growth 2- energy stores increase, cell continues to increase in size & mass, chloroplasts & mitochondria increase in size and divide
What does G1 checkpoint check for
-Chemicals needed for replication present
-Damage in DNA before synthesis
-Suitable in size
-Sufficient nutrients
What does G2 checkpoint check for
-All DNA has replicated without damage
-Cell is of correct size
Otherwise, daughter cells will not receive identical genetic information
Mitosis
Nuclear division- produces 2 genetically identical nuclei
Are them distributed unto two genetically identical daughter cells
I push miss around the corner
prophase, metaphase, anaphase, telophase
Prophase
(preparing)
-Chromosome condense (can now be seen easier)
-Each chromosome consists of 2 sister chromatids joined by a centromere
-Centrioles move towards poles
-Spindle fibres form
-Nucleolus & nuclear envelope breaks down
Metaphase
(middle)
-Chromosomes line up against the equator
-Spindle fibres attach to centromere
Anaphase
(pulled Apart. Arrow heads)
-Spindle fibres contract
-Centromere splits
-Daughter chromosomes pulled to opposite poles, centromere first
Telophase
(Two)
-Daughter chromosomes reach poles
-Chromosomes uncoil & lengthen
-Spindle fibres disintegrate
-Nuclear envelope & nucleolus reforms
Summary of mitosis
Animal Plant
most tissue. meristematic only
cell becomes round no change
Centrioles No
Spindles disappear Remain
Microfilaments No
Some cells lose ability to divide
eg. neurones, muscle cells
They leave the cycle temporarily or permanently due to:
a) Differentiation
b)Damaged DNA. Cell no longer viable so enter G0.
Importance of mitosis
-Growth of multicellular organisms
-repir damaged tissues
-replacement of cells
-asexual reproduction
Homologous chromosomes
46 (23 pairs)
Each pair is made up of one maternal and one paternal
Same: sequence of genes, same length, position of centromere
Different: Origins, alleles
how do we analyse the cell cycle?
flow cytometry:
- DNA stained with fluorescent dye
- passed through flow cytometer
- fluorescent intensity recorded
more DNA = more fluorescence ∴ increases G1 -> S -> G2
Cells which do not carry out mitosis
Mature RBC, neurones
Cell cycle control
Sequence & timing controlled by cyclins (protein)
which activate enzymes called cyclin-dependent kinases
which catalyse the addition of a phosphate group onto a protein, changing its tertiary structure
Specific CDKS control specific steps in cel cycle
What happens if errors are detected during cell cycle
p21 binds to CDKs
idea of complementary, blocks active site
This halts cell cycle at G1 stage in interphase
without p21, cancer. It is a tumour suppressor gene
Mutations to cyclin genes or CDKs can lead to failure to repair DNA-> cancer
Cytokenesis
Process of cytoplasm and two nuclei being divided to physically form 2 new daughter cells
Cytokenesis in animal cells
-CSM invaginates
-Cleaveage furrow forms in middle of cell
-csm pinches until 2 sides meet
-Cytoplasm & organelles are divided equally into 2 new daughter cells
Cytokenesis in plant cells
-Only in meristematic tissue
-vesicles from Golgi assemble on the equator= cell plate
-vesicles fuse with one another and the csm
-Cell wall forms along middle lamella
-Cytoplasm & organelles are divided equally into 2 new daughter cells
-Plant cells are inelastic due to cellulose cell wall
Synoptic link with cell cycle and cancer
-Negative regulator molecules (p53, p21) act primarily in G1 checkpoint and prevent cell from moving forward to synthesis until DNA is repaired
-p53 halts the cell cycle and recruits enzymes to repair DNA. If it cannot be repaired, apoptosis is initiated
Apoptosis
-Programmed cell death
(ordered and controlled process)
Necrosis
-unregulated cell death after trauma
-surface membrane ruptures, release of hydrolytic enzymes
Control of apoptosis
Cell signals are received from inside & outside of cells
-signals: p53, cytokines, hormones, growth factors etc
-Different signals induce apoptosis in different tissues
Apoptosis
-cell shrinks & chromatin in nucleus condenses (pyknosis)
-CSM breaks down & blebs form
-DNA breaks down
-Cell organelles break down
-Cell fragments into apoptotic bodies
-Macrophages engulf cell fragments
Uses of apoptosis
-fetal eg. toes
-puberty
-immune system (destruction of harmful immune cells)
-Formation of connections between neurones in brain
Stimuli
internal: eg. DNA change. Damage detected by cyclins, hals cell cycle -> apoptosis
external: attack by a pathogen
Detecting apoptosis & necrosis
-Flow cytometry
-Annexin V is used to detect apoptotic cells
-Binds to phosphatidylserine, a marker of apoptosis when in monolayer
nectrotic late apoptotic
Live ealy apoptotic
Stem cells
Unspecialised
Are potent
Can differentiate into specialised cells
Cell specialisation
At day 19, cells differentiate, producing specialised cells
Genes are switched on/off
Cells divide by mitosis to produce genetically identical clones
Groups of cells form tissues
Groups of tissues form Organs
Properties of stem cells
self-renewal: ability to divide many times while maintaining an unspecialised state
potency: ability to differentiate into specialised cells
Totipotent cells
(The prime minister)
Can form all cells in the body plus placental cells
Source: very early embryos, meristematic tissue
Pluripotent cells
Can form all cells in body but not placental cells
source: inner cell mass of blastocyst
eg use: cell replacement therapies- produce pancreatic cells to treat diabetes
Mutipotent cells
Adult stem cells can give rise to a limited number of cell types.
source: bone marrow, bone, umbilical chord
eg. uses: treat leukaemia, blood cancers, bone cancers
Problems with stem cells therapies
-Embryo rights, destruction of human embryos, hasn’t produced any viable long term treatments
-Better to turn differentiated cells back into pluripotent
Process of stem cell differentiation
-stem Cells undergoes mitosis
-Genes are switched on/off
-New proteins made
-cell becomes specialised
