The Cell Cycle Flashcards
What is the cell cycle?
- division of a cell resulting in formation of two genetically identical daughter cells.
What happens during interphase?
- DNA is replicated and checked for errors in the nucleus
- protein synthesis occurs in cytoplasm
- mitochondria grow and divide, increasing in number in the cytoplasm
- normal metabolic processes of cells occur
What are the three stages of interphase called?
- G1
- S
- G2
What happens in the G1 phase of interphase?
- first growth phase
- proteins from which organelles are synthesised and produced and organelles replicate
- the cell increases in size
What happens in the S phase of interphase?
- synthesis
- DNA is replicated in the nucleus
What happens in G2 phase of interphase?
- second growth phase
- cell continues to increase in size
- energy stores are increased
- duplicated DNA is checked for errors
What phases are in the cell cycle?
- interphase
- mitosis
- cytokinesis
What is mitosis?
- nuclear division
What is cytokinesis?
- cytoplasm divides and two cells are produced
When does the G0 stage happen permanently?
- differentiation: cell that has become specialised for specific function can no longer divide
- DNA become damaged, so no longer viable and won’t divide
What is the G0 phase?
- name given to the phase when the cell leaves the cell cycle
- temporary or permanently
When might the GO stage happen temporarily?
- white blood cells in an immune response
What do checkpoints do in the cell cycle?
- control mechanisms
- monitor and verify whether the process at each stage of the cell cycle have been accurately completed before the cell is allows to progress to next stage
What is the G1 checkpoint and what does it check for?
- end of G1 phase and before S phase
- checks for: cell size, nutrients, growth, DNA damage
What is the G2 checkpoint and what does it check for?
- end of G2 phase before mitosis
- checks for: cell size, DNA replication and DNA damage
What is the spindle assembly checkpoint and what does it check for?
- at the point in mitosis where all chromosomes are attached to spindles and aligned
- checks for: chromosome attachment to spindle
What happens if a checkpoint fails?
- cell is fixed/modified
- apoptosis (self destruction)
What is the difference between mitosis and cytokinesis?
- mitosis is the process of replicating and dividing the genome
- cytokinesis is the physical division of the cell
What is the importance of the G2 checkpoint?
- DNA has been checked for errors
- change in sequence of bases is a mutation
- leads to change in amino acid sequence
- function of protein dependent on 3D shape/tertiary structure
- tertiary structure dependent on primary structure
- primary structure is sequence of amino acids
What is a disadvantage of indefinite cell division?
- mutations occur during DNA replication
- indefinite replication increases chances of mutation/accumulation of mutations
- increased chance of harmful mutation
How is DNA usually replicated in eight hours in a eukaryotic cell?
- many origins of replication
- idea that simultaneous replication of different lengths
Why does it takes a shorter time to replicate the genome of a prokaryotic cell?
- genome is shorter
- has fewer genes/has no introns
What is mitosis?
- nuclear division before cell physically divides in two
Why is mitosis so important?
- new cells for growth and repair
- asexual production in eukaryotic cells e.g. amoeba species
- prokaryotic cells don’t have nucleus so go through process of binary fission
What’s a chromatid?
- two identical copies of DNA makes up chromosome in cell division
What’s a chromosome?
- a strand of genetic material in nucleus.
- each chromosome consists of DNA and histones
What’s an allele?
- different forms of the same gene
What’s crossing over?
- genetic info shared between homologous chromosomes
What’s a bivalent?
- pair of homologous chromosomes line up in prophase 1
What are histones?
- proteins associated with chromosomes
What is an homologous pair?
- pair of equivalent chromosomes with same structure and arrangement of genes
What happens in early prophase in mitosis?
- chromatin condenses and becomes inactive
- centrioles migrate in pairs to opposite poles
- nucelar envelope and nucleolus breaks up
What happens in late prophase in mitosis?
- chromosomes tightly coiled and visible as separate under microscope
- mitotic spindle begins to form at centrioles
What happens in metaphase in mitosis?
- mitotic spindle grows further and attaches to centromere of each chromosome
- fibres then arrange chromosomes to line up along the cell equator
What happens in anaphase in mitosis?
- centromere of each chromosome breaks
- sister chromatids separate into daughter chromosomes
- cell starts to elongate as cytokinesis begins
What happens in telophase in mitosis?
- new nuclear membranes and nucleoli form
- chromosomes start to unwind back into chromatin and are no longer visible under microscope
What is cytokinesis?
- cytoplasm is divided between two daughter cells
- each new cell enters interphase and resumes normal functions
How is cytokinesis different in plants and animals?
- plants have cell wall so cannot form cleavage furrow
- vesicles form instead to form new membrane and cell wall
Explain why we normally see chromosomes as a double structure containing two chromatids?
- chromosomes only become visible under the microscope during mitosis
- DNA needs to replicate for cell division. Chromosomes consist of two sister chromatids, which are identical copies of DNA.
Why is it essential that DNA replication results in two exact copies of the genetic material?
- so each daughter cell has identical DNA after mitosis/cell division
- and correct number of chromosomes
- diploid after mitosis and haploid after meiosis
Why are plant root tips are a good source of cells to examine for mitosis?
- they continually grow at regions called meristems
- meristems are good source of cells for studying mitosis as they are constantly dividing
- plant cells are easy to obtain and prepare for microscopy
What happens in prophase 1 in meiosis?
- chromosomes condense
- nuclear envelope disintegrates
- spindle fibres begin to form
- homologous chromosomes pair up forming bivalents
- crossing over occurs
What happens in metaphase 1 in meiosis?
- chromosomes line on cell equator
- spindle fibres attach to the centromeres
- independent assortment occurs
What happens in anaphase 1 in meiosis?
- homologous chromosomes are pulled (not apart) by the spindle fibres to the poles
- causes genetic variation
What happens in telophase 1 in meiosis?
- nuclear envelopes reform
- chromosomes uncoil
- undergoes cytokinesis
- haploid cells formed
How is meiosis similar to mitosis?
- exactly the same, apart from 4 haploid daughter cells produced
What causes genetic variation in meiosis and how?
- crossing over and independent assortment
- reduction (fertilisation)
- 23 chromosomes in haploid so lots of different combinations
Why is a reduction division necessary in the production of gametes?
- gametes are the sex cells and two sex cells must combine to produce a diploid offspring
- therefore gametes must contain only half the number of chromosomes/DNA
- be haploid otherwise with each new generation the number of chromosomes would increase
What is the importance of the creation of different allele combinations in populations?
- creating different allele pairs during meiosis is an important source of genetic variation in a population
- genetic variation is important for the process of natural selection
- gives individuals in a population characteristics that might confer an advantage in changing environment
- e.g. pathogen resistance
- if no genetic variation the entire population would be vulnerable to such an external factor and there would be no opportunity for adaptation
