all cells arise from other cells

Question 1

what is the cell cycle+outline stages

Answer 1

cycle of division with intermediate growth periods
1)interphase
2)mitosis or meiosis (nuclear division)
3)cytokenisis (cytoplasmic division)

Question 2

explain why the cell cycle doesn’t occur in some cells

Answer 2

after differentiation, some types of cells in multicellular organisms (e.g. neurons) no longer have the ability to divide

Question 3

what’s the difference between the cell cycle and mitosis

Answer 3

cell cycle includes growth period between divisions; mitosis is only 10% of the cycle and refers only to nuclear division

Question 4

what happens during interphase

Answer 4

G1:protein synthesis for replication e.g. tubulin for spindle fibres and cell size doubles

S: DNA replicates= chromosomes consist of 2 sister chromatids joined at a centromere

G2: organelles divide

Question 5

purpose of mitosis

Answer 5

produces 2 genetically identical daughter cells for:
-growth
-cell replacement / tissue repair
-asexual reproduction

Question 6

stages of mitosis

Answer 6

prophase
metaphase
anaphase
telophase

Question 7

what happens during prophase

Answer 7

1) CHROMOSOMES CONDENSE
become visible (Xshaped, 2 sister chromatids joined at centromere)
2) CENTRIOLES move to opposite poles of cell and mitotic spindle fibres form
3) NUCLEAR ENVELOPE AND NUCLEOLUS break down= chromosomes free in cytoplasm

Question 8

what happens during metaphase

Answer 8

sister chromatids line up at cell equator, attatched to the mitotic spindle by their centromeres

Question 9

what happens during anaphase

Answer 9

requires energy from ATP hydrolysis
1) spindle fibres contract = centromeres divide
2) sister chromatids seperate into 2 distinct chromosomes and are pulled to opposite poles of cell (looks like V shapes facing each other)
3) spindle fibres break down

Question 10

what happens during telophase

Answer 10

1) chromosomes decondense, becoming invisible
2) new nuclear envelopes form around each set of chromosomes = 2 new nuclei, each with 1 copy of each chromosome

Question 11

explain the procedure for the root tip squash experiment

Answer 11

1) prepare a temp mount of root tissue
2) focus an optical microscope on the slide. count total no. of cells in the field of view and no. of cells in a stage of mitosis
3) calculate mitotic index (proportion of cells undergoing mitosis

Question 12

outline how to prep a temp root tip mount

Answer 12

1) place root in HCL to halt cell division and hydrolyse middle lamella
2) stain root tip with a dye that binds to chromosomes
3) macerate tissues in water using mounted needle
4) press down coverslip and obtain single layer of cells - avoid trapping air bubbles

Question 13

name 2 dyes that bind to chromosomes

Answer 13

toluidine blue (blue)
acetic orcein (purple-red)

Question 14

why is only the root tip used when calculating a mitotic index

Answer 14

meristematic cells at root tip are actively undergoing mitosis

cells further from root tip are elongating rather than dividing

Question 15

what are tumour supressor genes

Answer 15

genes that code for proteins to trigger apoptosis (programmed death of damaged cells)/ slow cell cycle (e.g. p53 acts between G1 and S in interphase so damaged DNA cannot replicate)

Question 16

what are proto-oncogenes

Answer 16

genes that code for proteins to stimulate cell cycle to progress from one stage to the next

Question 17

how can mutation to tumour supressor genes and proto-oncogenes cause cancer

Answer 17

TUMOUR SUPRESSOR : no production of a protein needed to slow the cell cycle
PROTO-ONCOGENES : form permanently activated oncogenes
-disruption to cell cycle – uncontrolled cell division– tumour

Question 18

suggest how cancer treatments control the rate of cell division

Answer 18

disrupt the cell cycle:
-prevent DNA replication
-disrupt spindle formation= inhibit metaphase/anaphase

Question 19

how do prokaryotic cells replicate

Answer 19

BINARY FISSION
1) DNA loop replicates, both copies stay attatched to cell membrane. plasmids replicate in cytoplasm
2) cell elongates, seperating 2 DNA loops
3) cell membrane contracts and septum forms
4) cell splits into 2 identical progeny cells, each with 1 copy of the DNA loop but a variable number of plasmids

Question 20

why are viruses classified as non-living

Answer 20

they’re acellular
no cytoplasm; no metabolism; can’t self replicate

Question 21

how do viruses replicate

Answer 21

1) attatchment proteins bind to receptors on host cell membrane
2) enveloped viruses fuse with cell membrane or move in via endocytosis and release DNA/RNA into cytoplasm or viruses inject DNA/RNA
3) host cell used viral genetic info to synthesise new viral proteins
4) components of new viral particle assemble

Question 22

how do new viral particles leave the host cell

Answer 22

a) bud off and use cell membrane to form envelope
b) cause lysis of host cell

Question 23

why is it difficult to develop effective treatments of viruses

Answer 23

replicate inside living cells= difficult to kill them without killing host cells