Biology P4 random notes

[NIXORCollege]

Refractory Period
Represents a time during which the membrane cannot be depolarised again
During repolarisation and hyperpolarisation
Membrane is impermeable to Na+ ions / sodium ion channels closed
Sodium ions cannot enter axon
K+ ions move out as membrane is more permeable to K+ ions
Membrane becomes more negative than resting potential
Nerve impulses can only travel in one direction
Action potential can only depolarise the membrane in front
Membrane behind is recovering from refractory period (previous action potential)
Limits frequency with which neurones can transmit impulses

 

[NIXORCollege]

Factors Affecting the Speed of Conductance: Myelin, Axon Diameter, Temperature
Impulses travel faster in myelinated neurones → SALTATORY CONDUCTION
Schwann cells prevent diffusion of ions
Flow of current between adjacent nodes of Ranvier
\ depolarisation only at nodes of Ranvier
Action potential jumps from node to node
Temp affects speed of conduction of impulses
Higher temp increases rate of diffusion of ions
Impulses faster in an axon with larger diameter
Small cells / large surface area:volume ratio / ion leakage weakens membrane
Myelin stops ion leakage \ diameter only important for unmyelinated neurones

 

[NIXORCollege]

Pacinian Corpuscles
Found in dermis of skin, joints, tendons, external genitalia, internal organs
Structure
Layers (maellae) of connective tissue surround
Myelinated sensory neurone (nerve fibre ending) that have
Stretch-mediated Na+ channels
Round pacinian corpuscle has a resting potential
Stretch-mediated sodium channels restrict movement of ions
PRESSURE OPENS SODIUM CHANNELS
Entry of sodium ions
Causes depolarisation / membrane potential / generator potential
Threshold potential reached
Slight pressure / small generator potential / no depolarisation
Great pressure / more channels open / larger generator potential

 

[NIXORCollege]

Gametogenesis (→Formation of Gametes)
SAME in both sexes a) spermatogenesis, b) oogenesis
Multiplication of diploid cells by MITOSIS
Epithelium of seminiferous tubules multiplies Daughter cells are pushed towards lumen of tubule
Epithelial cell inside ovary of female fetus multiplies
GROWTH of daughter cells from mitotic divisions
Products of the growth phase divide by MEIOSIS producing haploid cells (46→23)
MATURATION of haploid daughter cells into gametes (eggs, sperm)
Heads are embedded in Sertoil cells
Prevent destruction of sperm by immune system
Sperm and body cells are genetically different
Provide nutrients Tails are projected into fluid-filled lumen

 

[NIXORCollege]

How gametogenesis differs in females
"b) Unequal cell division in meiosis / 1 ovum and tiny polar bodies produced
b) Primary oocytes form before birth / growth phase before birth
b) Pause in meiosis at prophase I / further development suspended until puberty
b) Pause in meiosis at metaphase II / meiosis not complete until fertilisation occurs"1

Follicle Development/Ovarian Cycle
Follicular stage [days1-13]
Anterior pituitary gland is secreting follicle-stimulating hormone FSH
FSH travels in bloodstream to ovary
Stimulates development (division) of follicle cells surrounding oocyte
Developing follicle cells secrete oestrogen
Stimulates proliferation of endometrium and its blood supply
Inhibits further secretion of FSH by negative feedback
Stimulates anterior pituitary gland to secrete luteinising hormone LH
LH brings about ovulation

Ovulation [day14]
        // Mature ovarian follicle ≈15mm in diameter
Mature ovarian follicle bursts and releases secondary oocyte (now called ovum!)
Corpus luteum forms from remaining follicle cells in ovary
Ovum passes down fallopian tube/oviduct towards uterus; fertilization now possible
Happens once a month, menstrual cycle ≈28days
Each ovary alternatively releases an ovum every ≈56days (→56/2)

Luteal phase [days15-28]
Corpus luteum secretes sex hormones
Progesterone continues to stimulate
Profileration of endometrium and its blood supply
Development of nutrient fluid glands in uterus lining
High levels of sex hormones inhibit secretion of LSH and LH
IF FERTILISATION DOES NOT OCCUR
Corpus luteum degenerates \ levels of sex hormones fall
Uterus lining breaks down; FSH is not inhibited anymore → cycle starts again

Uterine Cycle
Menstruation [days1-5] → Endometrium breaks down
Low levels of female sex hormones causes
uterus lining/endometrium to disintegrate
its blood vessels to rupture
Flow of blood (menses) passes out of the vagina
Proliferative phase [days6-13] → Endometrium rebuilds
Increased production of oestrogen by ovarian follicle
Secretory phase [days15-28] → Endometrium thickens and glands are secretory

 

[NIXORCollege]

Structure of a Mature Sperm Cell
Head: acrosome (enlarged lysosome → digestive enzymes → penetrate egg), nucleus
Middle piece: mitochondria, ATP needed for tail movement
Tail: flagellum, movement

Movement of Sperm in the Female Reproductive Tract
Sperm are ejaculated into the vagina / deposited outside the cervix
Alkalinity of semen neutralises acidic pH in vagina
Mucus allows sperm to swim through cervix / mucus is thin and watery during ovulation / glycoprotein chains run parallel
Wall of uterus has two distinct layers
Bulk of uterus wall consists of myometrium (→smooth muscle) / expels fetus at birth
Active muscular contractions during intercourse support sperm
Travel to oviduct in ≈5hours / survival rate of sperm ≈48hours
Endometrium is concerned with anchorage and nourishment of embryo
Sperm undergo capacitation while travelling
Acquire ability to fertilise 2° oocyte by removal of acrosome membrane proteins
Takes ≈6hours
Fertilisation occurs in the fallopian tube
Walls are lined with ciliated epithelia and contain smooth muscles
Egg moves to uterus via cilia movement and peristaltic muscle contraction
Contact between sperm and oocyte is by chance

Structure of the Egg
0.1mm (100um) in diameter. Sperm's head is only 2.5um across
Haploid nucleus is surrounded by cytoplasm / with enzymes and organelles
Yolk droplets contain proteins and lipids
Outside plasma membrane is a glycoprotein coat called a jelly coat

Acrosome Reaction and Penetration of the Oocyte Membrane
Acrosome reaction
Contact of jelly coat and sperm
Triggers Ca2+ to enter membrane of sperm
Causes acrosome to burst / releases enzymes / digest jelly coat
// enzymes: hyluronidase + acrosin
Sperm filament attaches to receptor on vitelline membrane
Sperm and egg plasma membranes fuse
Sperm nucleus enters egg, tail and middle piece remain outside
Depolarisation of membrane / blocks entry of more sperm
2° oocyte undergoes 2nd division of meiosis / produces ovum + second polar body
Nuclei (ovum + sperm) fuse forming a zygote

Female Infertility
Pituitary gland fails to produce FSH and prevents ovulation
TREATMENT: Injections of FSH
SIDE EFFECTS: May produce several eggs at the same time (→twins)
Too much oestrogen is secreted which inhibits FSH secretion
TREATMENT: non-steroidal drugs (e.g. clomiphene) which oppose action of oestrogen

Male Infertility
Semen contain too few sperm
TREATMENT: natural/synthetic androgens such as testosterone
// Viagra (sildenafil) is an enzyme inhibitor → causes smooth muscle surrounding erectile tissue to relax → more blood can be pumped into them during erection process

 

[NIXORCollege]

In Vitro Fertilisation (IVF)
FSH is injected in woman
Just before ovulation eggs are collected and matured
Fertilisation → collected sperm sample is added to collected mature egg
Nucleus of sperm is micro-injected into the egg
Fertilisation outside the body in a plastic disc
Advantage: possible to screen embryos for genetic defects
Maximum of three are transferred into the uterus

 

[xenaprongs]

"In substrate level phosphorylation, ATP synthesised using CHEMICAL POTENTIAL ENERGY but in oxidative phosphorylation, ATP synthesised using ELECTRICAL POTENTIAL ENERGY"
can u tel me hw does ATP is synthesised using ELECTRICAL POTENTIAL ENERGY in oxidative phosphorylation??
im cnfusd!!

 

[xenaprongs]

"In substrate level phosphorylation, ATP synthesised using CHEMICAL POTENTIAL ENERGY but in oxidative phosphorylation, ATP synthesised using ELECTRICAL POTENTIAL ENERGY"
can u tel me hw does ATP is synthesised using ELECTRICAL POTENTIAL ENERGY in oxidative phosphorylation??
im cnfusd!!

 

[zeebujha]

"In substrate level phosphorylation, ATP synthesised using CHEMICAL POTENTIAL ENERGY but in oxidative phosphorylation, ATP synthesised using ELECTRICAL POTENTIAL ENERGY"
can u tel me hw does ATP is synthesised using ELECTRICAL POTENTIAL ENERGY in oxidative phosphorylation??
im cnfusd!!

Substrate level phosphorylation is an entirely enzyme catalysed reaction in which phosphate group from a high energy intermediate is directly used to phosphorylate ADP. So, you are using the chemical energy of the high energy intermediate to phosphorylate ADP.

Oxidative phosphorylation uses the elctro-chemical gradient across the cristae to synthesize ATP. Here the Pi is not coming from any substance in particular(at least that is my understanding) and the phosphates are "free". We are using the kinetic energy of chemoosmosis (due to the resulting electrochemical gradient) to synthesise ATP from ADP and Pi.

 

[zeebujha]

Need to maintain rare breeds of animals: (From MS)
They can be used to form and maintain a gene bank. They are source of genetic variation and sources of alleles and could possibly have many unrecognized traits. So, they could be used for selective breeding in the future for possible resistance to pathogens and pests.

 

[zeebujha]

Process of selective breeding in Jersey cows:
-In Jerseys, the trait looked for is docility, high milk production and high content of fat in their milk
-Parents with some of these traits as well as general fitness (mental health + physical health) are made to mate.
-To test the parents, we can mate them on many occasions and check if the progeny have the suitable trait, particularly the heritability of the sex limited traits
-The offsprings are mated back with their parents when suitbale for background genes
-Artificial insemination can be used to maximise offspring from suitabl male and to allow long-distance mating
-Embryo transplantation can be used to maximise offspring from suitable female.
-This process carried out over MANY GENERATIONS

 

[zeebujha]

Spread of antibiotic resistance among bacteria:
Most bacteria reproduce rapidly and thus there is frequent DNA replication. This increases chances for mistakes during DNA replication process (mostly gene mutation) and this is compounded by the lack of gene editing enzymes which can proofread. Some of these mutations can provide resistance to the antibiotics and these mutations can be passed onto a large number of descendants via vertical transmission. In some cases, the mutation for resistance gene can be on plasmid. This gets transferred via horizontal transmission even to different species. This could be by conjugation, transformation or transduction. The bacteria with the resistance gene will be favored by selection and their allele frequency will increase over many generations

 

[zeebujha]

Dangers of gene therapy:
-ALLELE may be inserted within another needed gene altering the product of the needed gene
-ALLELE may be inserted into tissue other than target with unknown consequences
-ALLELE may be inserted into germ line and passed via gamete
-Virus may damage tissue

 

[zeebujha]

It is when genetic fingerprints show a much greater degree of similarity than might be expected, even amongst closely related individuals, that there is an indication of inbreeding

 

[zeebujha]

Anti-antibody: An antibody that attacks other antibodies,especially one produced in response to the injection of another antibody

 

[zeebujha]

Steps of Bioleaching:
1. Acidified water is pumped into large heaps of waste materials containing iron and copper sulfides, left from conventional mining
2. Thiobacillus ferro-oxidans oxidises iron (II) sulfide to iron (III) sulfate
3. The iron (III) ions oxidise copper sulfide to soluble copper sulphate. The solution is collected in shallow ponds
4. Scrap iron is put into the ponds and the reduction of Cu2+ ions by Fe metal allows metallic copper to be precipitated onto the iron
5. Metallic copper is scraped off the surface of the scrap iron and refined.

 

[zeebujha]

MAbs in vaccination in vaccination:
-Can be used to identify different strains of pathogens as monoclonal antibodies are monospecific for a particular epitope
-Identificatoin of immunogenic parts of viruses/bacteria
immunogenic: eliciting an immune response
-Use as subunit vaccines
subunit vaccine: a vaccine that contains isolated proteins from a virus, but lacks viral nucleic acid
-passive immunization
-which is especially helpful for immunologically compromised hosts

 

[zeebujha]

The prime assumption in selective breeding is that the selected trait is heritable

 

[zeebujha]

The main goal of genetic counselling is to provide information enabling parents to make their own informed decisions