2.1.6 Flashcards
What happens during interphase?
- dna replicated, checked for errors
- protein synthesis in cytoplasm
- mitochondria increases (grows and divides)
- chloroplasts grow and divide (in plants)
- normal metabolic processes (cell respiration)
What are the three stages of interphase?
G1 - first growth phase
S - synthesis phase
G2 - second growth phase
What happens during G1?
- proteins are produced (synthesise organelles)
- organelles replicate
- cell gets bigger
What happens during S?
DNA in nucleus is replicated
What happens during G2?
- cell gets bigger
- energy stores are increased
- duplicated DNA is checked for errors
What happens during the mitotic phase?
Mitosis : nucleus divides
Cytokinesis: cell divides
What is G0?
Phase where the cell leaves the cycle (temporarily or permanently)
When does G0 happen?
- differentiates (can no longer divide)
- cell DNA may be damaged (enters permanent arrest and no longer viable)
- age (leads to senescent cells)
What happens to lymphocytes in an immune response?
They can be stimulated to go back to cell cycle
When does a cell divide?
- at right size
- replicated Dna is error free
- chromosomes are in right position during mitosis
Why must these three characteristics be matched before a cell divides?
To ensure 2 identical daughter cells
What are checkpoints used for?
To monitor and verify whether phases have been accurately completed before going on to the next phase
What are the three checkpoints?
G1 checkpoint
G2 checkpoint
Spindle assembly checkpoint ( metaphase checkpoint)
What happens at G1 check point?
Checks for:
- cell size
- nutrients
- growth factors
- DNA damage
What happens if all is good at G1 checkpoint?
Triggers DNA replication
If not cell enters G0
What happens at G2 checkpoint?
Checks for:
- cell size
- DNA replication
- DNA damage
If all is good in G2 checkpoint then what happens?
It initiated molecular processes that signal the start of mitosis
What happens at the spindle assembly (metaphase) checkpoint?
It checks for chromosome attachment to spindle
What happens if all is good at metaphase checkpoint?
Mitosis proceeds
What is the order of stages of mitosis?
Prophase
Metaphase
Anaphase
Telophase
What are the six steps that happen in prophase?
- Chromatin fibres coil and condense making chromosomes
- nucleoulus disappears
- nuclear membrane starts to break down
- Chromatin fibres coil and condense making chromosomes
- Protein microtubules form spindle shaped structures
- 2 centrioles migrate to opposite sides of the pole (help with spindle formation)
- Spindle fibres attach to specific areas on centromeres and start moving chromosomes to middle
- By the end nuclear envelope has dissapeared
What happens during metaphase?
Chromosomes in the centre of cell (metaphase plate, equator)
What happens during anaphase?
-chromosomes divide and are pulled to opposite poles (through liquid cytosol) because of shortening spindle fibres
What happens during telophase?
Chromatids that reach each pole are now called chromosomes.
-nuclear envelope forms around each set of chromosomes
(Nucleolus is formed and chromosomes start to uncoil)
What else starts in telophase?
Cytokenisis
Describe what happens in cytokinesis in animals.
Cleavage furrow forms
Cell surface membrane is pulled inwards by cytoskeleton until its close enough to fuse in the middle.
Describe cytokinesis in plants.
- vesicles from golgi assemble in same place that metaphase plate was
- they fuse together with cell membrane
- dividing cell into two
- new sections of cell wall form along new sections of membrane
What are gametes?
Sex cells
What is zygote?
Fertilised egg
What type of division is meiosis and why?
Reduction division
Because for daughter cells (haploid) are produced
What are alleles?
Different versions of the same gene (gene variants ) they have the same locus
What happens during meiosis I?
First division is reduction division
Homologous pairs are split into two cells
What happens in meiosis I I?
Pair of chromatids in each daughter cell are separated making for haploid cells
What happens in prophase I?
-Chromosomes condense
-envelope disintegrates
-nucleolus disappears
-spindle formation
As chromosomes are brought together the entangle this can lead to crossing over
What happens in metaphase I?
-Homologous pairs of chromosomes assemble along metaphase
-Maternal and paternal chromosomes may end up facing either pole (independent assortment)
This leads to genetic variation
What happens during anaphase I?
Chromosomes are pulled to opposite poles
-forming recombinant chromatids
(Genes being exchanged between chromatids)
Lead to genetic variation
What is Chiasmata?
Points were chromatids break and rejoin during crossing over
What happens during telephone I?
Chromosomes assemble at each point -nuclear membrane reforms -chromosomes uncoil Cell undergoes cytokinesis making haploid
What are three things that can cause genetic variation?
- Crossing over
- Independent assortment
- genes been exchanged between chromatids
What happens during prophase 2?
- chromosomes condensed becoming visible
- nuclear envelope breaks down
- spindle formation starts
What happens in metaphase 2?
Line up along metaphase plate but due to IA and CO there’s more genetic variation
What happens in anaphase 2?
Chromatids are pulled after centromere division
Similar to mitosis
What happens in telophase 2?
- chromosomes uncoil and form chromatin
- nuclear envelope reforms
- nucleolus becomes visible
What’s the product of meiosis?
4 haploid daughter cells that are genetically different due to CO and IA
What are specialised cells?
Differentiated cells that have very special functions
Describe erythrocytes.
- biconcave (increase SA:V)
- no nuclei (more space for haemoglobin)
- flexible (squeeze through narrow capillaries)
Describe neutrophils.
- multi-lobed nucleus to squeeze through small gaps to get to infection sites
- granular cytoplasm has many lysosomes (have enzymes used to attack pathogens)
Describe sperm cells.
- tail/flagellum
- mitochondria
- acrosome (head) has digestive enzymes that penetrate ovum’s protective layers to penetrate
Describe palisade cells
- in mesophyll
- have chloroplasts that can move in cytoplasm to absorb more light
- large vacuole to maintain turgor pressure
- thin cell walls increase co2 diffusion
Describe root hair cells.
-long extensions called root hairs (maximise uptake of water and minerals)
Describe guard cells.
- have stomata
- guard cell cell wall is thicker on one side so cell doesn’t change shape symmetrically as volume changes
What are tissues?
A collection of differentiated calls with specialised functions/a function
What are the 4 main animal tissue catergories?
- nervous: transmission of electrical impulses
- epithelial: covers internal and external body surfaces
- muscle: contracts
- connective: hold tissues together (transport medium)
What is squamous epithelium?
- made of squamous epithelial cells
- 1 cell thick (rapid diffusion)
- forms lining of lungs
What is ciliated epithelium?
-hair like structures (cilia) move in rhythmic manner
-they are in trachea and move/sweep mucus away from lungs
-goblet cells release mucus to trap unwanted particles
Both these features are used to stop particles (like bacteria) from entering the lungs
What is cartilage?
-connective tissue that has: collagen and elastin
-made of chondrocyte cells embedded in extra cellular matrix
Used to stop bones from rubbing
What is muscle?
- contracts to move bones
- skeletal muscle fibres have myofibrils that have contractile proteins
What are the two main plant tissues?
- epidermis: covers plant surfaces
- vascular: transports water and minerals
What is epidermis?
- closely packed cells usually covered by waxy cuticle
- stomata is here
What is xylem tissue?
-made of elongated dead cells
-strengthened with waterproof material (lignin)- provides structural support
Transports water and minerals
What is phloem tissue?
-made of columns of sieve tube cells that are separated by perforated walls called sieve plates
Transport organic nutrients from where they are made (stem and leaves)
What is an organ?
Collection of tissues adapted to perform a particular function
Give an example of a human organ.
Heart - pumps blood
-muscle and connective tissue
Give an example of a plant organ.
Leaf - photosynthesis
Epidermis and vascular tissue
What is an organ system?
Number of organs
Give 3 examples of organ systems
- digestive
- cardiovascular
- gaseous exchange system
What are stem cells?
Undifferentiated cells that originate from mitosis/meiosis
When do stem cells stop dividing?
When they become specialised (enter G0 phase)
What does uncontrolled division lead to?
Formation of masses making tumours
May be cancerous
What is potency?
Ability to differentiate
What does totipotent mean?
-into any type of cell
e.g. a zygote from its first few divisions is totipotent
Eventually makes an organism
What does pluripotent mean?
-can form all tissue types not whole organisms
In early embryos
What does multipotent mean?
- can form only a range of cells within a certain tissue
e. g. haematopoetic stem cells (bone marrow)
- > can differentiate into various types of blood cells
What is the life span of erythrocytes?
120 days
What is the life span of neutrophils?
6 hours
What are the two types of stem cell sources in animals?
- embryonic
- tissue (adult) stem cells
What is the potency of embryonic stem cells?
-totipotent at early stages
After around 7 days a blastocyst is formed during pluripotent state
What is a blastocyst?
A mass of cells
What is the potency of adult stem cells?
(From birth onwards)
- are multipotent but can be artificially triggered to be pluripotent
Where is the plant stem cell source?
In meristematic tissues (meristems)
—> wherever there is growth (shoots and tips)
—> sandwiched between xylem and phloem tissues = vascular cambium, these cells can differentiate into cells in xylem or phloem
What is the potency of plant stem cells?
They are pluripotent
