3.2.2 All Cells Arise From Other Cells

Question 1

Meiosis vs Mitosis brief, importance of mitosis

Answer 1

Meiosis: Produces 4 daughter nuclei with half the number of chromosomes as the parent cell- haploids

Mitosis: Produces two daughter nuclei each with the same number of chromosomes as the parent cell and each other

Growth, repair, differentiation

Question 2

Draw and describe Stages of mitosis and steps (brief)

Answer 2

Interphase: Chromosomes invisible; DNA replicates

Prophase: Chromosomes appear, nucleus disappears

Metaphase: Chromosomes line up at equator, spindle fibres form

Anaphase: Chromatids pulled to opposite poles

Telophase:Chromatids at opposite poles and nucleus reforms

Cytokinesis: Cytoplasmic division

Question 3

What are the centrosomes? What’s their purpose? What do these regions contain? What are centromeres (unrelated)

Answer 3

Located near the nucleus
Not present in plants/ fungi
In cytoplasm
Animal centrosomes – region that contains 2 centrioles

Centriole- where protein spindle fibres are released from
Each centriole = 9 groups of microtubules (MT)
Spherical shape

Centromere- specialised DNA sequence of a chromosome that links a pair of sister chromatids

Question 4

Interphase- detailed Why?

Answer 4

PREPARATION STAGE- NOT AT REST

Considerable cellular activity
Actively synthesising proteins
DNA replicated
Centrosomes and organelles duplicated

Why? Preps for mitosis- need same no. of each organelle in daughter cells

Question 5

Prophase, slight diff btw early and late

Answer 5

Chromosomes are now visible and nuclear envelope disappears

Chromosomes condense (thicken/ become visible)
Centrioles move to opposite poles of the cell
Nucleolus “disappears”
Nuclear envelope breaks down

Early: early prophase - the nuclear membrane becomes more and more indistinct and the chromatin fibers become more and more packaged and condensed
Late: the nuclear membrane and the nucleolus finally vanishes completely, spindle fibres begin to form

Question 6

Metaphase, what are chromosomes made up of, what are chromatids joined by

Answer 6

Chromosomes arrange along equator of the cell

Spindle forms from centrioles
Chromosomes line up along spindle fibres across the equator of the cell
Spindle fibres attach to CETNROMERES and CHROMATIDS (MUST SAY THESE TWO)

A chromosomes is made up of 2 sister chromatids
Chromatids are joined at the centre by the centromere

Question 7

Anaphase- where energy is provided

Answer 7

Each chromatid is pulled to opposite poles

Contraction of spindle fibres cause sister chromatid to separate, centromeres divided into two
Chromatids are pulled to opposite poles of the cell

The energy for the process is provided by mitochondria, which gather around the spindle fibres.

Question 8

Telophase and Cytokinesis

Answer 8

Nuclear envelope reforms

Spindle fibres disintegrate
Nucleolus reforms
Nuclear membrane reforms
Chromosomes decondense

Cytokinesis:Cytoplasm divides into two daughter cells

Question 9

Cell division in prokaryotic cells- name and steps

Answer 9

binary fission

• The circular DNA molecule replicates and both copies attach to the cell membrane.
• The plasmids also replicate.
• The cell membrane begins to grow between the two DNA molecules and begins to pinch inward, dividing the cyt0plasm into two.
• A new cell wall forms between the two molecules of DNA, dividing the original cell into two identical daughter cells, each with a single copy of the circular DNA and a variable number of copies of the plasmids.

Question 10

Viral Replication Lytic (viral replication in book without last line)

Answer 10

non-living, they cannot undergo cell division. Instead they replicate

• by attaching co their host cell with the attachment proteins on their surface.
• They then inject their nucleic acid into the host cell.
• The genetic information on the injected viral nucleic acid then provides the ‘instructions’ for the host cell ‘s metabolic processes to start producing the viral components, nucleic acid, enzymes and structural proteins,
• which are then assembled into new viruses .
• then too many produced, cell lyses

Question 11

Virus Replication Lysogenic

Answer 11

non-living, they cannot undergo cell division. Instead they replicate

• by attaching co their host cell with the attachment proteins on their surface.
• They then inject their nucleic acid into the host cell.
• phage DNA is incorporated into the host genome, where it is passed on to subsequent generations

Question 12

What is the cell cycle, phases, which one takes up most of it, draw small pie chart to represent and label

Answer 12

Only some cells in multicellular organisms retain the ability to divide. Those that do not divide continuously but undergo a regular cycle of division separated by periods of cell growth. This is known as the cell cycle and has three stages:

1) Interphase. which occupies most of the cell cycle- 3 distinct stages (G1, S, G2)
2) Nuclear division (/mitosis/cell division) when the nucleus divides either into two (mitosis) or four (meiosis)
3) Cytokinesis- which follows nuclear division and is the process by which the cytoplasm divides to produce two new cells (mitosis) or four new cells (meiosis) (Topic 9.2). The length of a complete cell cycle varies greatly amongst organisms.

Typically, a mammalian cell takes about 24 hours to complete a cell cycle. of which about 90% is interphase.

Question 13

The Cell Cycle: Interphase-stages, what happens in each, acronym to remember

Answer 13

G1 = cell grows, proteins synthesised, organelles replicate → prepares for DNA replication

S (synthesis) = DNA is replicated

G2 = cell finishes growing, protein synthesised, and prepares for cell division

DOCTOR
DNA replication Organelle duplication Cell growth Transcription/Translation Obtain nutrients Respiration

Question 14

The Cell Cycle: M phase

Answer 14

Mitosis: Nuclear division
Cytokinesis: Cytoplasmic division

Question 15

Draw pie chart of cell cycle (G1, S, G2, M) and label where checkpoints are, what they check for
What is G0 state- what cells are in this state, name them and give examples

Answer 15

M(etaphase) checkpoint- checks spindle fibres are formed properly, chromatids are seperated equally

G1- nutrients, growth factors (so cell is right size) and DNA damage

G3- Cell size, DNA replication

G0 = a non-dividing stage
Quiescent cells ~ dormant (can re-enter G1) e.g neurones, heart tissue (unlike hair and nails, don’t need to divide rapidly)
Senescent cells ~ ageing/ deteriorating- destined for apoptosis

Question 16

What is cancer, damage in what two types of genes leads to it, what is a mutagen, examples of phys/chem/bio …ens, diff btw benign and malignant

Answer 16

Cancer is the result of damage to the genes that regulate mitosis and the cell cycle. This leads to uncontrolled growth and division of cells→tumour

Proto-oncogene = codes for proteins that stimulate cell growth/ proliferation
Tumour-suppressor gene = codes for proteins that inhibit cell cycle progression and promote apoptosis

Mutagen = an agent which causes changes to an organism’s genetic material
A mutagen which leads to the formation of cancer = a carcinogen

Phys- UV radiation, ionising radiation, gamma etc
Chem- food, cig smoke, reactive oxygen species
Bio- HPV, viruses

Question 17

6 Hallmarks of cancer

Answer 17

self-sufficiency in growth signals,

insensitivity to anti-growth signals,

tissue invasion and metastasis,

limitless replicative potential,

sustained angiogenesis (blood vessel growth),

evasion of apoptosis (cell death)

Question 18

What is metastasis, two steps

Answer 18

In metastasis, cancer cells break away from the original (primary) tumor, travel through the blood or lymph system, and form a new tumor in other organs or tissues of the body

1) Force blood vessel to wrap around cell and provide nutrients/O2/glucose, allows to divide
2) Break off cell, lodge into tissue, form another tumour.

Question 19

What process in mitosis could a drug target to prevent cell division?
What are the issues with chemo?
Why is it not given more frequently, why dose not increased? (Look at graph)

Answer 19

DNA replication
Spindle Formation

Issue: Normal, non-cancerous cells with a fast rate of division are also damaged by chemotherapy drugs.

Not frequently- need to give bosy time to replenish the healthy cells that were damaged
Not high dose- would kill too many healthy cells- balance between safety + effectiveness

Question 20

Sort into Healthy vs Cancer Cells
Lower level of dividing cells

Disorganised arrangement of cells

Loss of differentiated/ specialised functions

Cells arranged into discrete tissues

Some cells have differentiated structures

Cell size and shape relatively uniform

Normal expression of cell surface markers

Variation in cell size and shape

Elevated expression of cell surface markers

Higher levels of dividing cells

Answer 20

Healthy:
Lower level of dividing cells

Cells arranged into discrete tissues

Some cells have differentiated structures

Cell size and shape relatively uniform

Normal expression of cell surface markers

Cancer:
Disorganised arrangement of cells

Loss of differentiated/ specialised functions

Variation in cell size and shape

Elevated expression of cell surface markers

Higher levels of dividing cells

Question 21

What is the mitototic index? What does it tell you? How do you work it out?

Answer 21

The percentage of cells undergoing mitosis in a given number of cells
Mitotic index= (number of cells in mitosis/total number of cell) x 100

Question 22

What regulates the cell-cycle? Give examples (ameoba sisters video)

Answer 22

Proto-oncogenses: Positive regulators (allow moving forward in cycle)e.g CDK and Cyclin
Tumour-suppressor genes: Negative (stop) e.g p53 which encourages apoptosis

Question 23

Why can major injury to brain/spinal cord be so fatal?

Answer 23

Cells like neurones are in G0 phase, are not able to replicate so healing is difficult

Question 24

How to calculate cell size (using micrometer and graticule)

Answer 24

The eyepiece graticule is a glass disc in the eyepiece of a microscope.
Cells can be seen through a microscope and a micrometer can be used to calculate the actual size of the cells

Calibrating: In order to calculate cell size, the eyepiece graticule must be calibrated.
The graticule is calibrated by comparing the length of each division in the micrometer to the length of each division in the graticule.

E.g. Graticule calibration
E.g. 100 divisions on the eyepiece graticule are equal to 25.9 divisions on the micrometer.
In the micrometer, 100 divisions = 1mm.
This means that 1 division = 10µm and 100 eyepiece divisions = 25.9 × 10µm = 259µm.
This means that 1 eye piece division = 259 ÷s; 100µm = 2.59µm.
The ratio of micrometer division to eyepiece division is 10µm to 2.59µm

Calculating actual cell size:
Once the eyepiece graticule has been calibrated, actual cell size can be calculated using the equation:
Actual size = size of image ÷ magnification

E.g. Actual cell size 
The length of a cell is measured to be 33mm in an image drawn at a magnification of 400x. 
Size of image = 33mm = 33000 µm. 
Magnification = 400x. 
Actual size = 33000 ÷ 400 = 82.5µm.

Question 25

Required Practical: Preparation of Stained Squashes of Cells from Root Tips

Answer 25

1) Sample preparation
Wear gloves and use forceps to handle the tips.
Root tips must be sprouting (actively growing).
Place into 5 M hydrochloric acid.
After 5 minutes, rinse the tips in cold water in a watch glass

2) Cut the root tips
Using a sharp scalpel, cut root tips that are 2 mm long.
Place a root tip onto a microscope slide.
Ensure the slide is clean to reduce the chances of artefacts.

3) Staining
Carefully add 2-3 drops of stain and leave for two minutes.
Use a mounted needle to spread out the root tips into a thin layer.
Place a coverslip over the top of the tips.

4) Squashing
Squash down by applying force to the cover slip.
This could be with the flat end of a pencil, or the slide could be covered with a paper towel and pressed.
Force must be vertical or the cover slip may break and cause injury.

5) Viewing the sample
Place the slide on the microscope stage using the lowest power lens.
Focus the lens on the sample using first the coarse control and then the fine control.
Move the slide to see the range of cells. The cells closer to the tip will be those more actively dividing.
On a lens power of 400x, it should be possible to clearly see the chromosomes in the dividing cells.