Biology > Chapter 6 - Cell Division > Flashcards

Chapter 6 - Cell Division Flashcards

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1
Q

What is the cell cycle?

A

A highly ordered sequence of events that take place in a cell resulting in division of cells and production of 2 genetically identical daughter cells

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2
Q

What are the two broad stages of cell cycle?

A

Interphase and mitotic phase

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3
Q

What happens in interphase?

A

-Where cell spends majority of time
Major functions:
- DNA replicated and checked for errors in the nucleus
-Protein synthesis in the cytoplasm
- Mitochondria grow and divide so incre n. in cytoplasm
- Chloroplast grow and divide in plants
- Normal metabolic processes of cells occur

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4
Q

Name the 3 stages in interphase

A

G1 - proteins from which organelles are synthesized are produced and organelles replicated, cell incre size

S (synthesis) - DNA replicated in nucleus

G2 - Cell continues to grow in size, energy stored (glycogen) and dupes of DNA checked for errors

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5
Q

What are the two stages of the mitotic phase?

A

Mitosis (nucleus divides)

Cytokinesis

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6
Q

What is G0?

A

Phase where cell leaves the cell cycle, temporary or permanent

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7
Q

Why do cells go into the G0 phase?

A

Differentiation - cell becomes specialised to carry out particular functions, can’t divide further will carry out function and won’t enter cell cycle

DNA of cell could be damaged, no longer viable permanently in G0

As you age, the n. of these cells in your body increases/ Growing n. of senescent cells have been linked with many age related diseases (e.g. cancer)

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8
Q

Why does the cell cycle have checkpoints?

A

to ensure the fidelity of cell division, to control mechanisms of the cell

The checkpoints are monitors and verify whether process at each phase is accurately done before next

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9
Q

What happens at G1 checkpoint

A

-At the end of G1 phase before s, if cell passes then triggered to begin DNA replication if not goes to G0

Check for:
Cell size
DNA damage
Nutrients

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10
Q

What happens at G2 checkpoint?

A

Before mitotic phase, to pass checkpoint the DNA has to be checked without error for correct DNA replication

If passed the cell initiates the molecular processes that signal the beginning of mitosis

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11
Q

What happens in the metaphase checkpoint/ spindle fibre checkpoint?

A

Spindle assembly checkpoint

where all chromosomes should be attached to spindles and have aligned mitosis can’t occur if not done

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12
Q

Why do cells use mitosis?

A

Growth and repair
Replacement
In animals, plants & fungi

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13
Q

Why is mitosis so important?

A

Necessary for asexual reproduction- genetically identical offspring

Prokaryotic - binary fission

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14
Q

What happens before mitosis?

A

DNA is replicated in nucleus in interphase

Chromosome -> 2 chromatids (identical) joined be centromeres

So that there are 2 chromatids per chromosome

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15
Q

Name the stages of mitosis

A

Prophase
Metaphase
Anaphase
Telophase

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16
Q

Describe the steps in prophase

A
  1. Chromatin fibres begin to coil and condense to form chromosomes
  2. Nucleolus (area responsible for RNA synthesis) disappears and nuclear membrane breaks down
  3. Protein microtubules form spindle-shaped structures linking the opposite poles of the cells
  4. In animal cells the 2 centrioles (cylindric bundles of fibre) migrate to opposite poles of the cell
  5. Spidle fibres attach to specific areas on the centromeres and start to move the chromosomes to the centre of the cell
  6. By the end the nuclear envelope has disappeared.
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17
Q

What are the two stages of mitotic phase?

A

Mitosis - nucleus divides

Cytokinesis- Cytoplasm divides and 2 cells produced

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18
Q

Describe the stages of metaphase in mitosis

A
  1. Chromosomes are moved by the spindle fibres to form a plane in centre of cell

Metaphase plate and the chromosomes are held in position

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19
Q

What are the steps in anaphase?

A
  1. Centromeres holding together pairs of chromatids in each chromosome divide
  2. Chromatids are separated and pulled apart to opposite poles by the shortening of the spindle fibres
  3. Characteristic V shape of chromatids moving towards poles is because they are being dragged by their centromeres through the cytosol
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20
Q

Describe what happens in the final stage in mitosis

A

Telophase
The chromatids have reached the poles (now chromosomes)

  1. 2 new sets of chromosomes assemble at each pole and nuclear envelope reforms around them
  2. Chromosomes start to uncoil and the nucleolus is formed, cytokinesis begin
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21
Q

Suggest the stages involved in the cytokinesis in animal cells

A
  1. The cleavage furrows form around the middle of the cell
  2. Cell surface membrane pulled inwards by the cytoskeleton until its close enough to fuse around the middle forming 2 cells
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22
Q

Describe cytokinesis in plant cells

A

Plant cells have cell walls * cleavage furrows can’t form

  1. Vesicles in golgi apparatus begin to assemble (same place as metaplate)
  2. Vesicles fuse with each other and cell surface mem. divide into 2
  3. New sections of cell wall form along new sections of membrane
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23
Q

How many chromosomes does a diploid and a haploid have?

A

Diploid (46)

Haploid (23)

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24
Q

Why do gametes need to be haploid?

A

Because in sexual reproduction two sex cells (one from each parent) fuse to produce a fertilised egg

Egg develops into a zygote

Otherwise the n/ of chromosomes in a cell would double every round of reproduction

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25
What is meiosis?
A form of cell division where the nucleus divides twice resulting in halving of n. of chromosomes producing four haploid cells
26
How many times does the nucleus divide in meiosis?
Twice
27
Why is meiosis known as a reduction division?
Because 4 haploid cells are made from one diploid
28
What are homologous chromosomes?
Matching pair of chromosomes, one inherited from each parent
29
What are alleles?
Different versions of the same gene, will have the sae locus
30
Describe what happens during the two main stages of meiosis
Meiosis 1 : pairs of homologous chromosomes are separated into 2 cells, each intermediate cell will only have one full set of genes (haploid) Meiosis 2: similar to mitosis, the pairs of chromatids present in each daughter cell are separated, forming 4 haploid daughter cells
31
What happens in prophase 1 ?
1. Chromosomes condense, nuclear envelope disappears and spindle formation begins 2. Difference in phrop 1 is that the chromo. pair up forming bivalents (pairs of chromo.) 3. Chromosomes are large molecules of DNA, moving them through the cytoplasm as they are brought together results in the chromatids entangling 4. CROSSING OVER
32
What happens in metaphase 1?
1. Homologous chromosomes are moved by spindle fibres and assemble along metaplate 2. Orientation of each homologous pair on metaplate is random 3. INDEPENDANT ASSORMENT
33
Describe the steps involved in anaphase 1
1. Homologous chromosomes are pulled apart to opposite poles but stay joined together 2. Sections of DNA on 'sister chromatids' which were entangled during crossing over break of and rejoin 3. Point at which chromatids break and join is the chiasmata
34
What occurs in telophase 1?
1. Chromosomes assemble at each pole, nuclear membrane reforms 2. Chromosomes uncoil 3. Cytokinesis and divides - Reduction of chromosome n. from diploid -> haploid
35
Suggest the events in prophase 2
- Chromosomes still consist of 2 chromatids, they condense and become visible again 1. Nuclear envelope breaks down and spindle formation begins
36
How does metaphase 2 differ from 1?
The individual chromosomes assemble on the metaphase plate instead of the pair of homologous chromosomes
37
What happens in metaphase 2?
Chromosomes assemble on metaphase plate Due to crossing over the chromatids aren't identical INDEPENDANT ASSORTMENT
38
What is the difference between anaphase 2 and 1?
In anaphase 2 the chromatids of the individual chromosomes are being pulled to opposite poles after division instead of homol. chromosomes
39
What happens in telophase 2?
1. Chromatids assemble at the poles 2. Chromosomes uncoil and form chromatin 3. Nuclear envelope reforms and nucleolus becomes visible 4. Cytokinesis
40
Describe the organisation of multicellular organisms
``` Specialised cells Tissues Organs Organ system Organism ```
41
Define differentiated
When cells are specialised to carry out a very specific function
42
Suggest 3 examples of differentiated animal cells
Erythrocytes Neutrophils Sperm cells
43
Suggest adaptation which allow erythrocytes to carry out its function
- Flattered biconcave shape, increases SA:VOL - Don't have nuclei, ribosome, golgi apparatus to increase space for haem.. - Flexible so can squeeze through narrow capilaries
44
Describe how neutrophils are adapted to its function
- Multilobed nucleus, easier to squeeze through small gaps to get to the site of infection - Granular cytoplasm contains many lysosomes that contain enzymes used to attack pathogens (hydrolytic enzymes)
45
How are sperm cells adapted to its function?
- Tail/flagellum to allow movement - Have many mitochondria to supply energy needed to swim - Acrosome on the head end of the sperm contains digestive enzymes, which release to digest the protective layers around the ovum to allow fertilisation
46
What are palisade cells and how are they adapted?
Absorb large amounts of light for photo. - Cell are rectangular allowing them to be closely packed - Thin cell walls, increases the rate of diffusion of CO2 - Large vacuole to maintain turgor pressure - Many chloroplast to allow maximum amount of photo - Chloroplasts can move within cytoplasm to absorb max light
47
How are root hair cells adapted to its function?
-Long root hair cells which increase the SA of the cell, to maximise the uptake of water and minerals from soil
48
How are guard cells adapted?
- Can change shape to the stoma is closed to prevent further water loss - Cell wall of guard cell is thicker on one side so the cell doesn't change shape symmetrically
49
Define tissue
A collection of differentiated cells that have a specialised functions
50
What are the four main categories of tissues in animals?
- Nervous tissues (adapted to support the transmission of electrical impulses) - Epithelial tissue (to cover body surfaces inter and external) - Muscle tissue, adapted to contract - Connective tissue, adapted to either hold other tissues together or as transport medium
51
Suggest the adaptation of a squamous epithelium and give an example of where its found
- made of specialised squamous epithelial cell - Very thin due to flat cells and because one cell thick allowing rapid diffusion (e. g lining of the lungs)
52
Suggest adaptations of ciliated epithelium and where the tissue is found
- Made of ciliated epithelial cells - Cells have cilia on surface which move in rhythmic manner - Goblet cells in between cilia cells which release mucus to trap any unwanted particles (e.g. bacteria) - Cilia waft the mucus along Found in lining of trachea
53
How is cartilage adapted for its function?
Connective tissue found in ends and between bones - Has fibres of elastin and collagen - Firm and flexible connective tissue composed of chondrocyte cells embedded in the extracellular matrix - Prevents ends of bones rubbing together
54
What are the different muscle tissues and how adapated?
Skeletal muscle fibres- contain myofibrils which contain contractile proteins
55
Give 2 examples of different tissues in plants
Epidermis, adapted to cover surface of plant Vascular tissue, adapted for transport of water and nutrients
56
What is the epidermis and how is it adapted?
Single layer closely packed cells - Covered by waxy cutilce to reduce water loss - Stomata can open and close using guard cells, allow CO2 in and O2 out
57
How is the xylem tissue adapted?
- Transport of water and mineral through plants - Tissue is composed of vessel elements which are elongated dead cells - Walls strengthened with lignin
58
How is the phloem tissue adapted?
Transport of organic nutrients Has sieve tube elements separated by perforated walls called sieve plates
59
What is an organ?
Collection of tissues that are adapted to preform a particular function in an organism e.g. heart adapted to pump blood around the body, made of muscle and connective tissue
60
What is an organ system?
A number of organs working together to carry out a major function in the body
61
Give 3 examples of organ systems in animals
Digestive system- breaks down large insoluble molecules into small soluble ones Cardiovascular- moves blood around the body to provide transport system Gaseous exchange system- bring air to body so oxygen can be extracted and C02 expelled
62
What are stem cells?
Undifferentiated cells that are not adapted for any particular function and have the potential to become a range of cells Able to undergo cell division again and again, are a source of new cells necessary for growth, development and tissue repair
63
When does a stem cell enter G0?
When the stem cell has become specialised they lose the ability to divide
64
What is stem cell potency?
The cells ability to differentiate into different cell types
65
Name the 3 levels of stem cell potency
Totipotent Pluripotent Multopotent
66
What can totipotent cells do?
Differentiate into any type of cell - Fertilised egg or zygote and the 8-16 cells from its first few mitotic divisions are totipotent - Destined to eventually produce whole organisms - Can differentiate into extra-embryonic tissues like amnion or umbilicus
67
What can pluripotent cells specialise to ?
Form all tissues types but not whole organisms Present in early embryos Origin of different types of tissues in organism
68
What can multipotent cells do?
can only form a range of cells within a certain type of tissue e.g. haematopoietic stem cells in bone marrow give rbc
69
Why did unicellular organisms evolve to form multicellular?
Because groups of cells with different function working together as one unit is more efficient than single cells
70
What is the lifespan of rbc and wbc?
RBC -120 days | WBC- 6 hours
71
Where are animal stem cells sourced from?
Embryonic stem cells - Present at very early stages - Totipotent, cell mass called blastocyst Adult tissue - Present from birth - Found in bone marrow - Multipotent - Also sourced from umbilical cord (invasive surgery not needed)
72
Where are plant stem cells sourced from?
- In meristems, found in tips of roots and shoots that are growing - Also in between the phloem and xylem (in the cambium)
73
Suggest the uses of stem cells
- Heart disease - Type 1 diabetes, own immune system destroys the insulin producing cells - Alzheimer's, brain cells are destroyed - Spinal injuries, - Birth defects
74
Where is stem cell technology already used in?
- Treatment of burns - Drug trials - Developmental biology
75
Why are many people against the use of stem cells?
1. Some say life begins at conception therefore the destruction of embryos is murder 2. Lack of consensus as to when the embryo itself has rights 3. Who owns the genetic material 4. Religious objections
76
Suggest the differences between DNA and RNA
- The pentose sugar is deoxyribose for DNA and ribose for RNA - In RNA the thymine in the base composition is replaced by Uracil - RNA is single stranded and DNA is double stranded
77
Suggest differences between Mitosis and Meiosis
- one division in mitosis and 2 in meiosis - 2 diploid daughter cells that are genetically identical produced - 4 haploid daughter cells produced are genetically different from parent cell
78
Discuss the ways in which genetic variation is produced including the role of nuclear division
- Independent assortment of homologous chromosomes in metaphase 1 - Homologous chromosomes, one from each parent, produces a large number of allele combi - Crossing over in prophase 1 - So chromatids have new combination of alleles - Mutations, changes the base sequence - DNA checks didn't recognise the damage - Fertilisation is random - Maybe one more or less chromosome present
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