cells, viruses and reproduction (2) Flashcards
name the 6 features of prokaryotic cells
nucleiod
plasmids
70s ribosomes
cell wall
pili
flagella
what is a nucleon
an irregular shaped region of cytoplasm
where a loop of DNA is located
what are plasmids
rings of DNA found in some bacterial cells
contains non-essential genes
they can also be used for genetic modification
what are ribosomes
the site of protein synthesis
what is the cell wall
peptidoglycan cell wall provides strength and support
may have a slime capsule to prevent cessation
what are pili
hairs which help them attach themselves
what is the flagella
a tail like feature which allows for movement
outline the process of gram staining
stain the culture with crystal violet
rinse
add iodine (then remove)
add alcohol
counterstain with red safranin
dry + examine under microscope
explain the results of gram staining
gram positive stains purple
- thick peptidoglycan layer (insoluble in alcohol)
gram negative stains pink
- thin peptidoglycan layer (soluble in alcohol)
why do some bacteria react differently to antibiotics?
some antibiotics inhibit peptidoglycan formation
e.g. penicillin
- this doesn’t work on gram negative as they have a thin peptidoglycan layer + an outer membrane
role of nucleus
stores genetic information + controls cell activities
role of nucleolus
the site of ribosomes production
role of the rough ER
many ribosomes attached for protein synthesis + transport
role of the smooth ER
the site of lipid synthesis
role of mitochondria
the site of respiration
role of centrioles
involved in cell division
role of lysosomes
contain digestive enzymes e.g. hydrolytic enzymes
role of the golgi apparatus
processes proteins and lipids + produces lysosomes
role of the cell wall
provides protection + support
role of chloroplasts
contains chlorophyll for photosynthesis
role of the vacuole
stores stuff e.g. cell sap in plants
role of tonoplasts
the vacuoles membranes
which regulates the movement of ions
why are specimen stained
the stain binds to structures
what is immunostaining
when labelled antibodies are added to a sample
making specific proteins visible
what is magnification
how much bigger the image is than the object
what is resolution
how far apart two points can be before they are seen as one
outline the process of using a light microscope
shine ray of light onto specimen
different structures absorb different amounts + wavelengths of light
the reflected light is then transmitted to the observer
outline the process of using a transmission electron microscope
pass a beam of electrons through specimen
more dense structures appear darker as they absorb more electrons
outline the process of using a scanning electron microscope
focus a beam of electrons onto specimens surface
reflected electrons hit collecting device
and are amplifies to produce a 3D image
outline the limitations of electron microscopes
it is expensive
the specimen must be in a vacuum
therefore dead
produces black + white images
how are viruses classified
by their
shape + structure (enveloped vs non-enveloped)
and
type of nucleic acid (RNA vs DNA and single stranded vs double stranded)
give an example of a DNA virus
lambda page
give examples and features of RNA viruses
tobacco mosaic
- non-enveloped
- positive ssRNA
meaning it can be directly translated into proteins
ebola
- enveloped
- negative ssRNA
meaning it must to be transcribed before it can be translated
give an example of a RNA retrovirus
HIV
outline the lysogenic cycle
- non-virulent virus injects nucleic acid into host cell
- viral DNA is replicated when host cell divides
- virus produces repressor proteins to inhibit transcription
- latent virus enters lytic pathway when host cell is damaged or immune system is weak
(this is mostly done by phages infecting bacteria)
outline the lytic cycle
- virulent virus injects nucleic acid into host cell
- viral DNA replicated immediately + independently of the host cells DNA
- cell matures + bursts
- large numbers of virus released
why are viruses classified as non-living
they cannot reproduce without a host
how do antiviral drugs work
drug must interfere with a process in viral life cycle e.g. reverse transcription (RNA->DNA) in HIV you can have an enzyme inhibitor. A drug could also be a cytokine that increases immune response (e.g. interferon)
A drug may stop viral DNA polymerase working (e.g. anti-herpes drug)
how do antiviral drugs inhibit viral replication
they do this by
- targeting viral antigens
preventing entry into host cell - targeting viral enzymes
preventing DNA replication + assembly of vision
e.g. reverse transcriptase inhibitor for HIV
list 3 ethical problems associated with the use of untested drugs during epidemics
who to treat first
chance of unanticipated side effects
severely ill patients cannot give informed consent
name the stages in the cell cycle
interphase, mitosis + cytokinesis
define mitosis
process by which a cell divides into 2 identical daughter cells
what is the significance of mitosis
growth and repair
and
asexual reproduction
outline the stages in interphase
G1-
cell synthesises proteins for replication
S phase-
DNA replicates
G2-
organelles divide
outline the stages of mitosis
prophase
metaphase
anaphase
telophase
outline prophase
chromosomes condense
spindle fibres form
and
nuclear envelope breaks down
outline metaphase
chromosomes line up along the equator in a single file line
and
spindle fibres attach at the centromere
outline anaphase
sister chromatids move to opposite poles
and
centromeres divide
outline telophase
chromosomes decondense
spindle fibres break down
and
nuclear envelope reforms
outline cytokinesis
cytoplasm divides
and
parent cell becomes 2 identical daughter cells
define meiosis
process by which a cell divides into 4 genetically different haploid cells
outline meiosis 1
prophase 1- same as mitosis
**+ crossing over **of non-sister chromatids -> making recombinant alleles -> with new allele combinations
metaphase I - same as mitosis except homologous pairs of chromosomes instead line up along the equator
anaphase I - same as mitosis except homologous pairs of chromosomes instead move to the poles
+ independent assortment- which way the paternal and maternal chromosomes will be pulled is random
telophase 1- same as mitosis…
results in 2 haploid cells
outline meiosis 2
all the same as mitosis
prophase 2- same as mitosis
metaphase 2- same as mitosis (single-file)
anaphase 2- same as mitosis (chromatids separate)
telophase 2- same as mitosis
results in 4 genetically different daughter cells (after cytokinesis)
how does meiosis bring about genetic variation
- crossing over during prophase 1
- independent assortment of homologous chromosomes + sister chromatids
resulting in new combinations of alleles in gametes
what is a chromosome mutation e.g. translocation
when a chromosome is changed on a large scale rather than just at 1 place
so much DNA is lost/gained on a chromosome that it can often be observed with a microscope
e.g. translocation- when part of a chromosome jumps onto another chromosome
what is non-disjunction
when chromosomes fail to separate correctly + gametes have
1 extra chromosome (polysomy)
e.g. downs syndrome
or
1 missing chromosomes (monosomy) e.g. turners syndrome
what are the types of gametogenesis
oogenesis + spermatogenesis
outline the process of oogenesis
diploid primordial gremlin cell
mitosis
oogonia
growth period
primary oocytes
first meiotic division (separating chromosomes)
1 haploid secondary oocyte + 1 polar body
second meiotic division (separating chromatids)
secondary oocyte -> haploid ootid + polar body
polar body -> divides into 2
= ootid + 3 polar bodies (degenerate as ootid develops)
ootid differentiates = ovum
outline the process of spermatogenesis
1 diploid primordial germline cell
mitosis
2 diploid spermatogonia
loads of mitosis
many diploid primary spermatocytes
each primary spermatocyte
first meiotic division (separating homologous chromosomes)
2 haploid secondary spermatocytes
second meiotic division (separating chromatids)
4 haploid spermatids
spermatids differentiate to gain
- flagellum
- acrosome
- many mitochondria
what is the importance of mitosis in spermatogenesis
to keep on making more spermatogonia
in order to make more spermatocytes forever
outline the process of fertilisation
- enzymes in acrosome of sperm head digest zone pellucida
- sperm head fuses with the ovums cell membrane -> allowing sperm nucleus to enter
- cortical granules from ovum are released via exocytosis -> cortical reaction -> causing the zona pellucida to harden -> preventing polyspermy
- nuclei fuse -> forming a diploid zygote
outline the formation of a blastocyst
zygote -> several mitotic divisions
-> embryo (2 or more cells)
-> morula (solid ball of identical cells -> which are totipotent)
further divisions, differentiation + cavity formation
-> blastocyst (pluripotent)
describe the structure of a blastocyst
fluid filled cavity
inner cell mass -> develops into foetus
outer layer -> develops into placenta
what and where are the plant gametes found
pollen grains in anther
and
embryo sac in ovule
how are the male gametes in plants formed
diploid microspore cell
meiosis
4x haploid microspores
mitosis
they mature into 4x pollen grains (2x haploid nuclei each)
how are the female gametes in plants formed
diploid megaspore mother cell
meiosis
1x haploid megaspore + 3x polar bodies (these degenerate then are reabsorbed)
3x mitotic divisions + differentiation
1x megaspore (made up of 8x haploid nuclei- of which 2 are polar nuclei + 1 is the female gamete)
how do male nuclei reach the embryo sac
- pollen grain germinates on stigma
- mitosis of generative nucleus -> produces 2x male gametes -> which will enter the embryo sac
- enzymes digest the surrounding tissue -> which will allow the tube to grow + provides nutrients -> enabling the pollen tube to grow down the style -> then through micropyle -> into the embryo sac
outline the process of double fertilisation
what sucrose conc do pollen tubes grow best in
near isotonic -> as its the same as conc as inside -> preventing osmotic damage
