Topic 3

Question 1

Explain Nucleus - Eukaryote

Answer 1

-Controls cell activity by controlling transcription of DNA
-Large, surrounded by nuclear envelope
-Envelope contains pores for mRNA to move in and out
-Contains nucleolus (makes ribosomes)
-Contains chromatin (made of DNA and proteins)

Question 2

Explain lysosome - Eukaryote

Answer 2

-Round organelle, no clear internal structure
-Contains digestive enzymes, kept seperate from cytoplasm
-Used to digest invading cells or break down work out components of cells

Question 3

Explain ribosome - Eukaryote

Answer 3

-Small organelle, free floating or attached to RER
-Made of proteins and RNA
-Site where proteins are made

Question 4

Explain RER and SER - Eukaryote

Answer 4

-System of membranes enclosing fluid filled space
-SIte where folding and processing of proteins made at ribosomes

-Similar to RER, no ribosomes
-Synthesies and processes LIPIDS

Question 5

Explain golgi apparatus - Eukaryote

Answer 5

-Group of fluid filled, membrane-bound, flattened sacs
-Processes and packages new lipids and proteins
-Synthesises lysosomes

Question 6

Explain mitrochondrion - Eukaryote

Answer 6

-Oval shaped, double membrane
-Inner membrane folded, forms structure named cristae
-Inside is named the matrix, houses enzymes involved in respiration
-Site of aerobic respiratiom
-Where ATP is producd
-Found in large numbers

Question 7

Explain protein production

Answer 7

-Proteins are made at ribosomes
-Proteins produced on RER are folded and processed, e.g sugar chains added
-Vesicled and transported to golgi apparatus for more processing
-Vesicled once more to be transported around cell
-Extracellular enzymes move to cell surface to be secreted

Question 8

Recall prokaryote structure (9x)

Answer 8

-Cytoplasm, has no membrane-bound organelles & smaller ribosomes
-Fragellum, long, hair-like, rotates for cell movement
-Circular DNA, long and coiled up
-Plasmids, small loops of DNA, contains genes for antibiotic resistance
-Mesosomes, inward folds in plasma membrane
-Capsule, made of secreted slime to protect bacteria from immune systems
-Pili, short, hair-like, helps stick to other cells, used to transfer genetic material between cells
-Cell wall, support, made from murein, which is a glycoprotein
-Plasma membrane, mainly made of lipids and proteins, control ins and outs of substances

Question 9

Explain Mitosis

Answer 9

-Parent cell divides to produce 2 genetically identical daughter cells
-Mitosis is needed for growth and repair of tissues, and for asexual reproduction
-Mitosis -> Gap Phase 1 -> Interphase -> Gap Phase 2 -> Mitosis

Question 10

Explain stages of mitosis: interphase and prophase

Answer 10

-DNA unravels and replicates (doubling genetic content)
-Organelles replicate, ATP content increases

-Chromosomes condense, shorter and fatter
-Bundles of centrioles move to opposite poles of cell
-Network of spindle (protein) fibres form
-Nuclear envelope breaks down and chromomoses lie free in cytoplasm

Question 11

Explain stages of mitosis: metaphase and anaphase

Answer 11

-Chromosomes line up along at middle of cell
-Chromosomes attach to spindle fibres by their centromere

-Centromere divides, seperation of each pair of sister chromatids
-Spindle contracts, pulls chromatids to opposite poles of spindle by their centromere

Question 12

Explain stages of mitsosis: telophase and cytokinesis

Answer 12

-Chromatids uncoil, becomes long and thin, now named chromsomes
-Nuclear envelope forms around each set of chromosomes, now there are 2 nuclei

-Cytoplasms divides
-Now there are 2 daughter cells which are gentically identical to original and eachother

Question 13

Core Pratical: Root Tips

Answer 13

-Cut 1cm from tip of growing root e.g onion (tip is where growth occurs)
-Prepare boiling tube of 1M HCl, into a water bath of 60deg
-Place root tip into boiling tube, incubate for 5mins
-Pipette to rinse root tip withcold water, leave to dry on paper towel
-Mounted needle to break tip open and spread cells thinly
-Small drop of stain, leave for 2mins (makes chromosomes more visible)
-Cover slip over cells and push firmly to squash and thinen tissue, makes light easy to pass through too
-Use light microscope
-Mitotic index = number of cels w visible chromo / total num cells observed

Question 14

Recall structure of egg cell

Answer 14

-Cell plasma membrane
-Follicle cells, protective coating
-Zona pellucida, protective glycoprotein layer which perm must penetrate
-Nucleus

Question 15

Explain fertilisation

Answer 15

-Occurs in oviduct
-Sperm swims to egg cell
-When sperm contacts zona pellucida, acrosomal reaction occurs
-Digestive enzymes in the sperm head is released, digestion of zona pellucida occurs
-Sperm head fuses with cell membrane, cortical reaction occurs
-Egg releases contents of vesicles (from cytoplasm) into the C.M, Z.P space
-Cortical granules released there release chemicals which harden/thicken the Z.P
-Ensures one sperm penetrates, protects egg cell from multiple fertilisations
-Nucleus of sperm fuses with nucleus of egg (fertilisation)

Question 16

Explain stages of meiosis

Answer 16

-DNA replicates, 2 identical copies of each chromosome (chromatids)
-DNA condenses, forms double-armed chromosomes made from 2 sis chromatids
-Chromosomes arranged into homologous pairs e.g num 1 and num 1 pair, crossing over can occur
-1st division, homologous pairs seperate, halving chromosome number
-2nd division: pairs of sister chromatids seperate
-Four new daughter cells produced, genetically differ.

Question 17

Explain crossing over

Answer 17

-Before 1st division, homologous pairs pair up
-Two chromatids in each pair, twist around one another
-Twisted bits break off their original and join onto their new chromatid
-Chromatids have same number of genes. just differing combos of alleles
-4 new cells formed from meiosis contain chromatids with differing alleles

Question 18

Explain independant assortment of chromosomes

Answer 18

-4 daughter cells formed from meiosis have different combinations of chromosomes
-When gametes are produced, you have half genes from mum and dad
-When gametes produced, different combos of said maternal and paternal genes go into each cell

Question 19

Define totipotency and pluripotency

Answer 19

-Ability to produce all cell types in an organism including extraembryonic cells (placenta and umbillical cord cells)

-Ability for a stem cell to produce all specialised cells in an organism not including extraembryonic ones

Question 20

Explain transcription factors

Answer 20

-Controls gene expression by altering rate of transcription
-Proteins that bind to DNA to activate or deactivate genes by increasing or decreasing rate of transcription
-In prokaryotes, T.F binds to operons to control gene expressions

Question 21

Explain lac operon in E.Coli

Answer 21

-Ecoli is bacterium that respires glucose, it uses lactose if glucose is unavailable
-Genes producing enzymes needed to respire lactose is found on lac operon
-Lac operon has 3 structural genes, LacZ, Y and A, which produce proteins that aid bacteria digesting lactose

Question 22

Explain lactose not present in E.Coli

Answer 22

-Regulatory gene lacll produces lac repressor, a T.F that binds to operator site out of presence of lactose
-This blocks transcription as RNA polymerase cannot bind to the promoter region
-Structural genes are not transcribed

Question 23

Explain lactose present in E.Coli

Answer 23

-Lactose binds to repressor changing its shape so it cannot bind to operator site
-RNA polymerase can bind to the promoter region and begin its transcription of structural genes (lacz, y and A)

Question 24

Explain where stem cells can come from

Answer 24

-From adult tissues: stem cells found in bone marrow, limited differentiation
-Simple operation, very little risk however much discomfort

-From embroyos: created in IVF where egg cells are fertilised by sperm outside the womb, totipotent stem cell.
-Embroyos must be 4-5 days old, their stem cells to be removed resulting in embryo destroyed
-Ethical issue: killing of potential fetus

Question 25

Explain continuous and discontinuous variation

Answer 25

-Continuous: value has a range such as mass or height
-Discontinuous: value has a distinct category such as eye colour or shoe size or blood group
-Variation of phenotype is influenced by variation of genotype and the enviroment
-Enviromental influence could be diet, influences height and cancer

Question 26

Explain increasing methylation on DNA

Answer 26

-Methylation of DNA represses a gene
-Addition of a methyl group to DNA coding for a gene where cyotosine and guanine are next to eachother in a gene
-Leads to changes to DNA structure, proteins and enzymes needed for transcriptions cannot bind to gene and will not be expressed

Question 27

Explain histone modification and how it affects gene expression

Answer 27

-How condense a chromatid is affects the accessibility of DNA, wrapped around a histone, by a protein or enzyme
-Epigenetic modification includes adding or removing acetyl group
-Adding acetyl makes the chromatin less condense allowing it to be more accessible
-Removing acetyl groups makes the chromatin highly condensed making it less accessible by enzymes, disallowing transcription - it is repressed