2 - DNA and Cells Flashcards
components of a eukaryotic cell (11)
- cell surface membrane
- nucleus
- mitochondria
- chloroplasts
- Golgi
- vesicles
- lysosomes
- RER
- SER
- cell wall
- cell vacuole
function and structure of cell surface membrane
- fluid phospholipid bilayer
- controls what enters and leaves the cell using embedded transport and channel proteins
function and structure of nucleus
- 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
function and structure of mitochondria
- 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
function and structure of chloroplasts
- 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
function and structure of Golgi apparatus
- 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
function and structure of vesicles
- small hollow spheres of membrane
- transport large molecules to cell surface membrane for exocytosis
function and structure of lysosomes
- small spheres of membrane containing digestive enzymes
- fuse with vesicle containing engulfed pathogen to digest it, along with dead organelles and cells
function and structure of RER
- 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
function and structure of SER
- flattened discs of membranes with no ribosomes
- synthesise lipids and carbohydrates to be transported throughout the cell, including Golgi
function and structure of cell wall
- 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
function and structure of vacuole
- membrane bound structure filled with inorganic and organic materials and water
- store harmful or waste products, and proteins for seed germination
define resolving power
- 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
why do optical microscopes have low resolving power?
their wavelength is too long
wavelength of visible light
400-700nm
wavelength of electron wave
0.005nm
what can you see with a TEM
detailed cross section of a very thin specimen
limitation of electron microscopes
has to been in a vacuum, so can’t look at live specimens
what formula gives us magnification?
magnification = image / actual
outline the steps for cell fractionation
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
order the 3 things that come out as sediment during ultracentrifugation
nucleus
mitochondria
chloroplasts
how does DNA transcription and translation work?
https://www.youtube.com/watch?v=gG7uCskUOrA
what does DNA helicase do?
unzips the DNA by breaking the hydrogen bonds between the corresponding bases
what does RNA polymerase do?
joins up the corresponding RNA bases during transcription to make mRNA, making phosphodiester bonds
when can mutations occur?
DNA replication
are there any mechanisms to prevent mutations?
a checking mechanism in eukaryotes goes through the DNA, checking for lumps caused by incorrect pairing
name the 6 types of mutations
- substitution
- deletion
- addition
- inversion
- duplication
- translocation
name the 3 types of substitution
- silent - no effect
- nonsense - makes stop codon
- missense - makes a new amino acid
which type of mutation is least harmful and why?
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.
which type of mutation is most harmful and why?
deletion or insertion, because they cause a frame shift, so every codon after the deletion/insertion is affected
why do not all mutations change the amino acid that is made?
degenerate nature of DNA
how does mutation in the number of chromosomes arise?
spontaneously by chromosome non-disjunction during meiosis
what is DNA like in prokaryotic cells?
short, circular and not associated with proteins
what is DNA like in eukaryotic cells?
long, linear and associated with histone proteins
which organelles of a eukaryotic cell also contain DNA?
mitochondria and chloroplasts
what does a gene code for?
the amino acid sequence of a polypeptide, and a functional RNA
what is the fixed position of a gene on the DNA called?
locus
how do we describe the DNA code?
- universal
- non overlapping
- degenerate
what are the sequences within a gene called and what do they do?
- exons which code for amino acid sequences
- introns which separate exons and don’t code for anything
how do prokaryotic cells differ from eukaryotic cells
- 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
which enzyme converts mRNA to chromosomal DNA
reverse transcriptase
which process removes base sequences from pre-RNA to form mRNA
splicing
which bases are purines and which are pyrimidines?
G and A purines
C and T pyrimidines
difference between purines and pyrimidines
purines have 2 carbon rings
pyrimidines have 1 carbon ring
how is genetic variation ensured in meiosis
- homologous chromosomes pair up
- independent segregation
- maternal and paternal chromosomes reshuffled in any combination
- crossing over leads to exchange of alleles between homologous chromosomes
