Cell division

Question 1

what is the cell cycle?

Answer 1

-regulated cell division with intermediate growth periods
1. interphase
2. mitosis or meiosis (nuclear division)
3. cytokinesis (cytoplasmic division)

Question 2

what happens in interphase?

Answer 2

-G1 = cell synthesizes proteins for replication e.g. tubulin spindle fibres and cell size doubles
-S = DNA replicates -> chromosomes consist of 2 sister chromatids joined at a centromere
-G2 = organelles divide

Question 3

what’s the purpose of mitosis?

Answer 3

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

Question 4

stages of mitosis

Answer 4

PMAT

Question 5

outline what happens in prophase

Answer 5

-chromosomes condense, becoming visible
-centrioles move to opposite poles of the cell and mitotic spindle fibres form
-nuclear envelope breaks down - releases chromosomes into cytoplasm

Question 6

outline what happens in metaphase

Answer 6

-sister chromatids line up at equator

Question 7

outline what happens in anaphase

Answer 7

requires energy from ATP hydrolysis
-spindle fibres contract causing centromeres to divide
-sister chromatids separate into 2 distinct chromosomes and are pulled to opposite poles (v-shaped now)
-spindle fibres break down

Question 8

outline what happens in telophase

Answer 8

-chromosomes decondense becoming invisible again
-new nuclear envelope forms around each new set of chromosomes = 2 nuclei, each with 1 copy of each chromosome

Question 9

what happens during cytokinesis?

Answer 9

-CSM cleavage furrow forms
-contractile division of cytoplasm

Question 10

how is the cell cycle regulated?

Answer 10

-there are checkpoints regulated by cell-signalling proteins, to ensure damaged cells don’t progress to the next stage of the cell cycle
-cyclin-dependent kinase (CDK) enzymes phosphorylate proteins that initiate next phase of reactions

Question 11

describe what happens at each key checkpoint in the cell cycle

Answer 11

-between G1 and S, cell checks for DNA damage (via action of p53 (a protein that acts as a tumour suppressor - keeps cells from dividing and growing in an uncontrolled way). After restriction point (once a cell passes this point it is obligated to continue and undergo mitosis), cell enters cycle

-between G2 and M, cell checks the chromosome replication

-at metaphase checkpoint, cell checks that sister chromatids have attached to the spindle correctly

Question 12

what is meiosis?

Answer 12

-type of cell division
-produces 4 genetically different haploid daughter cells
-cells with half the number of chromosomes found in parent cells
-they are called gametes

Question 13

what happens during meiosis I?

Answer 13

-homologous chromosomes pair to form bivalents
-crossing over (exchange of sections of genetic material) occurs at chiasmata
-cell divides into 2 - homologous chromosomes separate randomly - each cell contains either maternal or paternal copy

Question 14

what are homologous chromosomes?

Answer 14

-a pair of chromosomes with same genetic info - 1 maternal, 1 paternal
-some alleles may be the same while others are different

Question 15

what happens during meiosis II?

Answer 15

-independent segregation/assortment of sister chromatids
-each cell divides again, producing 4 haploid cells

Question 16

how does meiosis introduce genetic variation?

Answer 16

-crossing over during meiosis I
-independent assortment (random segregation) of homologous chromosomes and sister chromatids
-results in new combinations of alleles

Question 17

how do cells become specialised?

Answer 17

-cells undergo a process called differential gene expression
-where some genes are expressed while some are silenced due to cell differentiation mediated by transcription factors - cells produce proteins that determine their structure and function

Question 18

what is a transcription factor?

Answer 18

-a protein that controls the transcription of genes so that only certain parts of the DNA are expressed e.g. in order to allow a cell to specialise

Question 19

how do transcription factors work?

Answer 19

-move from cytoplasm into nucleus
-bind to promoter region upstream of target gene
-makes it easier or more difficult for RNA polymerase to bind to gene - this increases or decreases rate of transcription

Question 20

what’s a stem cell?

Answer 20

-undifferentiated cells that have to ability to divide indefinitely and turn into other specific cell types

Question 21

name and define 4 types of stem cell

Answer 21

totipotent - can develop into ANY cell type, including placenta and embryo
pluripotent - can develop into ANY cell type, excluding placenta and embryo
multipotent - can only develop into a few different types of cell
unipotent - can only differentiate into one type of cell

Question 22

uses of stem cells

Answer 22

-repair of damaged tissue e.g. cardiomyocytes after myocardial infarction
-drug testing on artificially grown tissues
-treating neurological diseases like Parkinson’s or Alzheimer’s
-researching developmental biology e.g. formation of organs, embryos

Question 23

describe erythrocytes

Answer 23

-RBC
-biconcave shape
-no nucleus
-lots of haemoglobin to carry oxygen

Question 24

describe neutrophils

Answer 24

-WBC(leukocyte)
-multi-lobed nucleus
-contains many lysosomes (destroy invading cells)
-they engulf foreign material

Question 25

how do specialised cells in the blood form?

Answer 25

-multipotent cells in bone marrow differentiate into: erythrocytes - which have a short lifespan and can't undergo mitosis because they don't have nucleus leukocytes including neutrophils

Question 26

describe the structure of squamous and ciliated epithelia

Answer 26

simple squamous epithelium - single smooth layer of squamous cells (thin and flat with round nucleus) fixed in place by basement membrane ciliated epithelium - made of ciliated epithelial cells (column-shaped with surface projections called cilia that move in a synchronised pattern)

Question 27

describe the specialised structure of a spermatozoa

Answer 27

-acrosome in the head to penetrate egg's outer layer -many mitochondria - for aerobic resp. ATP provides energy for the tail (undulipodium/flagellum) and propel itself towards ovum -haploid nucleus so fertilisation restores diploid chromosome number

Question 28

describe the structure and function of palisade cell

Answer 28

-specialised to absorb light energy for photosynthesis therefore contain many chloroplasts -they occupy large SA for smooth gas exchange -they have thin cell wall for larger penetration of light into cell -they are long and cylindrical so can be packed closely together but with small air pockets for carbon dioxide to diffuse in

Question 29

describe structure and function of guard cell

Answer 29

-form tiny spores called stomata -> they control gas exchange and water loss (transpiration) - when turgid, stoma open and when flaccid, stoma closes -needs ATP to actively transport potassium ions from surrounding epidermal cells into guard cells, lowering water potential

Question 30

describe structure and function of root hair cells

Answer 30

-hair-like projections to increase SA for absorption of water/carrier proteins needed for active transport of mineral ions like nitrates (ATP needed)

Question 31

what are meristems?

Answer 31

-totipotent undifferentiated plant cells that can develop into various types of plant cells like phloem and xylem

Question 32

describe structure of a vascular bundle

Answer 32

-cambium (meristematic tissue) -phloem tissue -xylem tissue

Question 33

describe structure of phloem tissue

Answer 33

-sieve tube elements: form a tube to transport sucrose in the dissolved form of sap -companion cells: involved in ATP production for active loading of sucrose into sieve tubes -plasmodesmata: gaps between cell walls where the cytoplasm links, allowing substances to flow in

Question 34

describe structure of xylem tissue

Answer 34

-vessel elements: lignified secondary walls for mechanical strength and waterproofing; perforated end walls for rapid water flow -tracheids: tapered ends for close packing; pits for lateral water movement; no cytoplasm or nucleus

Question 35

what are the 3 types of muscle?

Answer 35

smooth - walls of blood vessels and intestines cardiac - exclusively found in the heart skeletal - attached to incompressible skeleton by tendons