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Biology A Level > 2 - DNA and Cells > Flashcards

2 - DNA and Cells Flashcards

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1
Q

components of a eukaryotic cell (11)

A
  • cell surface membrane
  • nucleus
  • mitochondria
  • chloroplasts
  • Golgi
  • vesicles
  • lysosomes
  • RER
  • SER
  • cell wall
  • cell vacuole
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2
Q

function and structure of cell surface membrane

A
  • fluid phospholipid bilayer

- controls what enters and leaves the cell using embedded transport and channel proteins

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3
Q

function and structure of nucleus

A
  • nucleolus is a dense spherical region of protein and nucleic acid. Synthesises ribosomal RNA and assembles ribosomes
  • nuclear envelope controls entry and exit of materials, allowing the passage of RNA
  • chromosomes are linear strands of DNA which are coiled over histones and folded so compact
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4
Q

function and structure of mitochondria

A
  • inside is matrix fluid, which contains proteins, lipids, circular DNA and ribosomes
  • double membrane, inside membrane folded into cristae
  • synthesises ATP through aerobic respiration
  • some proteins synthesised in mitochondria, suggesting bacterial origin
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5
Q

function and structure of chloroplasts

A
  • double membrane with internal membrane stacks called grana
  • grana surrounded by stroma, fluid containing proteins, circular DNA, ribosomes and starch grains
  • contain chlorophyll which traps light energy for photosynthesis
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6
Q

function and structure of Golgi apparatus

A
  • label proteins to allow for sorting and form vesicles (packages) of carbs, proteins and lipids
  • add carbs to proteins to form glycoproteins
  • stacks of flattened sacs of membranes, surrounded by vesicles
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7
Q

function and structure of vesicles

A
  • small hollow spheres of membrane

- transport large molecules to cell surface membrane for exocytosis

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8
Q

function and structure of lysosomes

A
  • small spheres of membrane containing digestive enzymes

- fuse with vesicle containing engulfed pathogen to digest it, along with dead organelles and cells

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9
Q

function and structure of RER

A
  • flattened discs of membranes with embedded ribosomes on the outside
  • synthesises proteins to be embedded in the cell membrane or transported out of the cell, not in cytoplasm
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10
Q

function and structure of SER

A
  • flattened discs of membranes with no ribosomes

- synthesise lipids and carbohydrates to be transported throughout the cell, including Golgi

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11
Q

function and structure of cell wall

A
  • made of cellulose
  • provides mechanical strength and support to withstand turgor pressure
  • regulates diffusion and helps prevent water loss
  • sends signals for the cell to enter the cell cycle
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12
Q

function and structure of vacuole

A
  • membrane bound structure filled with inorganic and organic materials and water
  • store harmful or waste products, and proteins for seed germination
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13
Q

define resolving power

A
  • the ability to distinguish between two objects that are close to each other
  • or the smallest distance below which two discrete objects will be seen as one
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14
Q

why do optical microscopes have low resolving power?

A

their wavelength is too long

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15
Q

wavelength of visible light

A

400-700nm

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16
Q

wavelength of electron wave

A

0.005nm

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17
Q

what can you see with a TEM

A

detailed cross section of a very thin specimen

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18
Q

limitation of electron microscopes

A

has to been in a vacuum, so can’t look at live specimens

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19
Q

what formula gives us magnification?

A

magnification = image / actual

20
Q

outline the steps for cell fractionation

A

1 - put cut up tissue in cold buffered solution with same water potential as tissue
2 - homogenise it by stirring with paddle
3 - filter homogenate to remove cell fragments and intact cells
4 - ultracentrifuge at different speeds until you get what you want

21
Q

order the 3 things that come out as sediment during ultracentrifugation

A

nucleus
mitochondria
chloroplasts

22
Q

how does DNA transcription and translation work?

A

https://www.youtube.com/watch?v=gG7uCskUOrA

23
Q

what does DNA helicase do?

A

unzips the DNA by breaking the hydrogen bonds between the corresponding bases

24
Q

what does RNA polymerase do?

A

joins up the corresponding RNA bases during transcription to make mRNA, making phosphodiester bonds

25
Q

when can mutations occur?

A

DNA replication

26
Q

are there any mechanisms to prevent mutations?

A

a checking mechanism in eukaryotes goes through the DNA, checking for lumps caused by incorrect pairing

27
Q

name the 6 types of mutations

A
  • substitution
  • deletion
  • addition
  • inversion
  • duplication
  • translocation
28
Q

name the 3 types of substitution

A
  • silent - no effect
  • nonsense - makes stop codon
  • missense - makes a new amino acid
29
Q

which type of mutation is least harmful and why?

A

substitution, because only one amino acid can be changed and even then if only the last base is changed, it won’t affect the amino acid that is made.

30
Q

which type of mutation is most harmful and why?

A

deletion or insertion, because they cause a frame shift, so every codon after the deletion/insertion is affected

31
Q

why do not all mutations change the amino acid that is made?

A

degenerate nature of DNA

32
Q

how does mutation in the number of chromosomes arise?

A

spontaneously by chromosome non-disjunction during meiosis

33
Q

what is DNA like in prokaryotic cells?

A

short, circular and not associated with proteins

34
Q

what is DNA like in eukaryotic cells?

A

long, linear and associated with histone proteins

35
Q

which organelles of a eukaryotic cell also contain DNA?

A

mitochondria and chloroplasts

36
Q

what does a gene code for?

A

the amino acid sequence of a polypeptide, and a functional RNA

37
Q

what is the fixed position of a gene on the DNA called?

A

locus

38
Q

how do we describe the DNA code?

A
  • universal
  • non overlapping
  • degenerate
39
Q

what are the sequences within a gene called and what do they do?

A
  • exons which code for amino acid sequences

- introns which separate exons and don’t code for anything

40
Q

how do prokaryotic cells differ from eukaryotic cells

A
  • much smaller
  • don’t have membrane-bound organelles
  • have smaller ribosomes
  • don’t have a nucleus but a singular circular DNA molecule that is free in the cytoplasm
  • have a cell wall that contains murein a glycoprotein
  • some have one or more plasmids
  • some have a slime capsule or flagellum
41
Q

which enzyme converts mRNA to chromosomal DNA

A

reverse transcriptase

42
Q

which process removes base sequences from pre-RNA to form mRNA

A

splicing

43
Q

which bases are purines and which are pyrimidines?

A

G and A purines

C and T pyrimidines

44
Q

difference between purines and pyrimidines

A

purines have 2 carbon rings

pyrimidines have 1 carbon ring

45
Q

how is genetic variation ensured in meiosis

A
  • homologous chromosomes pair up
  • independent segregation
  • maternal and paternal chromosomes reshuffled in any combination
  • crossing over leads to exchange of alleles between homologous chromosomes

Biology A Level (11 decks)

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