IB biology: topic 1: origin of cells / cell division

what is endosymbiotic theory?

mitochondria were once free-living prokaryotic organisms that had developed aerobic respiration.

larger prokaryotes took them in and allowed them to live in their cytoplasm, creating the modern eukaryotic animal cell.

what is evidence for mitochondria and chloroplasts being independent prokaryotes at some point in history? (4)

they have their own genes, on a circular DNA molecule like that of prokaryotes.

they have their own 70s ribosomes of a size and shape typical of some prokaryotes.

they transcribe their DNA and use mRNA to synthesise some of their own proteins.

they can only be produced by division of pre-existing mitochondria and chloroplasts.

how did Pasteur disprove the theory of spontaneous generation?

using swan-necked bottles, he poured in broth that had been boiled to kill off organisms and broth that had been left as a control.

fungi and organisms appeared in the unboiled flasks but not in the boiled ones.

only after Pasteur snapped the necks of the bottles did microorganisms grow in all flasks.

how were carbon compounds found to have potentially originated from in the early atmosphere? (experiment)

Miller and Urey passed steam through a mixture of methane, hydrogen and ammonia and electrical discharged were used to simulate lightning. they found that amino acids and other carbon compounds were produced.

how were carbon compounds found to have formed polymers in the early atmosphere? (research)

inorganic chemicals are carried by hot water in deep-sea vents - these chemicals represent readily accessible energy which can be used for the assembly of carbon compounds into polymers.

how were membranes found to be formed? (research)

carbon compounds like phospholipids would have naturally assembled into bilayers - these bilayers readily form vesicles resembling the plasma membrane of cells.

how was a mechanism for inheritance developed? (research)

in early evolution, RNA may have been genetic material as it can store information but is both self-replicating and can act as a catalyst

(necessary to have enzymes for replication but genes for enzyme formation)/

what is mitosis?

the division of the nucleus into two genetically identical daughter nuclei

what is mitosis used for?

growth (including embryonic development),

tissue repair,

asexual reproduction.

what is the cell cycle?

the sequence of events between one cell division and the next.

what are the two main phases of the cell cycle?

interphase and cell division

what occurs during interphase? (overview)

DNA replication in nucleus and protein synthesis in cytoplasm.

numbers of mitochondria and chloroplasts increase.

plant cells synthesise cellulose to add to their cell
walls.

what are the 3 phases of interphase?

G1, S, G2

what happens during G1?

cellular contents are duplicated (but not chromosomes), normal cell activities

what happens during S?

each of the chromosomes is duplicated

what is a chromosome made up of? (2)

two identical chromatids,

centromere,

what are the arms of a chromosome known as?

p arm (shorter, on top) and q arm (longer, on bottom)

what is supercoiling?

the repeated coiling of the DNA molecule to make it shorter and wider

how long are DNA molecules?

more than 50mm (50,000 micrometres)

what is another name for the process of supercoiling?

condensation

if you unravel a chromosome, would do you get?

a DNA double helix is wrapped around histone proteins to form nucleosomes.

a series of nucleosomes form a cylindrical coil which forms a chromatin fibre.

further coiling of the chromatin fibre forms sister chromatids.

what are the stages of mitosis? (4)

prophase, metaphase, anaphase, telophase

what happens during prophase?

1. chromosomes become shorter and fatter by supercoiling.
2. the nucleolus breaks down
3. microtubules grow
4. nuclear membrane breaks down

what happens during metaphase?

1. microtubules continue to grow and attach to the centromeres of each chromosome
2. the microtubules are put under tension to see if the attachment is correct

what happens during anaphase?

1. the centromere divides and sister chromatids divide
2. microtubules pull them rapidly towards the poles of the cell

what happens during telophase?

1. chromatids reach the poles and are now called chromosomes
2. chromosomes are pulled into a right group
3. nuclear membrane reforms
4. chromosomes uncoil and a nucleolus is formed

what happens towards the end of mitosis?

cytokinesis

what is cytokinesis?

the division of a cell into two daughter cells

what happens in cytokinesis in animal cells?

1. a ring of contractile protein inside the membrane at the equator allows the plasma membrane is pulled inwards to form a cleavage furrow
2. the cell is pinched apart, when the furrow reaches the centre of the cell two new daughter cells form

what are the contractile proteins involved in cytokinesis in animal cells?

actin and myosin

what happens during cytokinesis in plant cells?

1. vesicles are moved to the equator where they fuse to form tubular structures across it
2. these merge to form two layers of membrane of the daughter cells
3. pectins are brought by vesicles and deposited by exocytosis between two new membranes
4. this forms the middle lamella that will link new cell walls
5. both daughter cells then bring cellulose to the equator and deposit it by exocytosis

what does cyclin do?

control the cell cycle

what is cyclin?

a group of proteins that ensure tasks are performed at the correct time and that the cell only moves on to the next stage when appropriate

how do cyclins control the cell cycle?

1. cyclins bind to enzymes called cyclin-dependent kinases
2. kinases become active and attach phosphate groups to other proteins
3. this activates the proteins which carry out specific tasks for the phases

what are the four main types of cyclin in humans?

cyclin d,

cyclin e,

cyclin a,

cyclin b

what happens if cyclin does not reach the threshold concentration?

the cell does not progress to the next stage

what does cyclin D do?

triggers the cell to move from G0 to G1 and from G1 to S

what does cyclin E do?

prepares the cell for DNA replication in S phase

what does cyclin A do?

activates DNA replication inside the nucleus in S phase

what does cyclin B do?

promotes the assembly of the mitotic spindle and other tasks in the cytoplasm to prepare for mitosis

what are tumours?

abnormal groups of cells which appear at any time and anywhere in the body

what are benign tumours?

tumours where the cells adhere to each other, do not invade nearby tissue/spread and are unlikely to cause harm

what are malignant tumours?

tumours where cells become detached, move elsewhere, form secondary tumours and are very likely to be life-threatening.

what is metastasis?

spread of a primary tumour

what are causes of cancers? (2)

carcinogens, mutations

what are carcinogens?

chemicals and agents which cause carcinomas

what are mutagens?

chemicals and high energy radiation which cause genetic mutations

what are examples of mutagens?

benzene (chemical) and UV light (high energy ionisation)

what are mutations?

random changes to the base sequence of genes (most do not cause cancer)

what are oncogenes?

genes that can become cancer-causing after mutating (not many)

how are tumour cells formed?

when several mutations occur in the same cell