A level Biology: Post your doubts here!

[Dukeofwin]

And also this :
Q: state that a gene is a sequence of nucleotides as part of a DNA molecule, which codes for a polypeptide
and state that a mutation is a change in the sequence that may result in an altered polypeptide

 

[Unreal]

Q: describe the way in which the nucleotide sequence codes for the amino acid sequence in a polypeptide
with reference to the nucleotide sequence for HbA (normal) and HbS (sickle cell) alleles of the gene for
the β -haemoglobin polypeptide.

(This is from Syllabus! Could anyone answer this?)

The nucleotide sequence for an amino acid consists of a triplet code. Due to a mutation a different nucleotide sequence can arise.
In this case base substitution occurs where one Thymine from CTT is substituted with Adenine forming CAT. Therefore the amino acid valine forms instead of glutamate. (Allele for HbA contains CTT while allele for HbS contains CAT) Formation of HbS leads to sickle cell anaemia.

Thats as far as i know. Someone else might have a better one.

 

[Dukeofwin]

The nucleotide sequence for an amino acid consists of a triplet code. Due to a mutation a different nucleotide sequence can arise.
In this case base substitution occurs where one Thymine from CTT is substituted with Adenine forming CAT. Therefore the amino acid valine forms instead of glutamate. (Allele for HbA contains CTT while allele for HbS contains CAT) Formation of HbS leads to sickle cell anaemia.

Thats as far as i know. Someone else might have a better one.

Yeah thats right but I also got it,

Heamoglobin is made from 2 Alpha Chains and 2 Beta Chains. Sometimes In the Beta Chain the nucleotide sequence for Gulatamine is replace by Valine (like you said from CTT to CAT). As a result of this mutation the structure of Heamoglobin (WHEN IT IS NOT COMBINED WITH OXYGEN) changes and it forms a Half moon like structure(forms HbS). And because of this it is ineffective in carrying Oxygen

 

[Khadija.95]

Umm guys. Can somebody please help me with valves? I know that:

• tricuspid has 3 valves and is on the right side
• bicuspid has 2 valves and is on the left side
• bicuspid is also called the mitral valve (is this true? Please confirm.)

So the tricuspid and bicuspid valves are ATRI-VENTRICULAR valves. What and where are the SEMILUNAR VALVES?? Pleasee help :/

 

[Khadija.95]

Oh wait, are the Pulmonic Valves also called Semilunar Valves?? :|

 

[devonaoki]

CAN ANYONE HELP ME WITH FULL AS BIOLOGY REVISION NOTES

 

[6Astarstudent]

Oh wait, are the Pulmonic Valves also called Semilunar Valves?? :|

When you see "Pulmo" it is related to the lungs, in this case you're half right. The pulmonic valve is the semilunar valve between the pulmonary artery and the right ventricle.

Umm guys. Can somebody please help me with valves? I know that:

• tricuspid has 3 valves and is on the right side
• bicuspid has 2 valves and is on the left side
• bicuspid is also called the mitral valve (is this true? Please confirm.)

So the tricuspid and bicuspid valves are ATRI-VENTRICULAR valves. What and where are the SEMILUNAR VALVES?? Pleasee help :/

Bicuspid = mitral valve
semilunar valves are valve between arteries and ventricle. (aorta/left ventricle) (pulmonary artery/right ventricle)

 

[Khadija.95]

When you see "Pulmo" it is related to the lungs, in this case you're half right. The pulmonic valve is the semilunar valve between the pulmonary artery and the right ventricle.


Bicuspid = mitral valve
semilunar valves are valve between arteries and ventricle. (aorta/left ventricle) (pulmonary artery/right ventricle)

Jazak'Allah! Thank you sooo muchh! Could you also tell me if it's true that Lung Cancer starts due to mutations, causing uncontrollable division of epithelial cells in the airways?

 

[6Astarstudent]

Jazak'Allah! Thank you sooo muchh! Could you also tell me if it's true that Lung Cancer starts due to mutations, causing uncontrollable division of epithelial cells in the airways?

For A level biology this is true because the out of all the chemicals we learn (Carbon Monoxide, Tar, Nicotine), tar is actually the only carcinogen. Of course there are lots more, like the radio active isotopes, benzyl compounds.
Since tar only settles on the epithelial cells (like 99% of the time), so it will only cause uncontrollable mitosis of epithelial cells causing malignant tumours which is the cause of cancer. (By the way tar causes cancer by switching off the tumour suppression genes)

 

[Khadija.95]

For A level biology this is true because the out of all the chemicals we learn (Carbon Monoxide, Tar, Nicotine), tar is actually the only carcinogen. Of course there are lots more, like the radio active isotopes, benzyl compounds.
Since tar only settles on the epithelial cells (like 99% of the time), so it will only cause uncontrollable mitosis of epithelial cells causing malignant tumours which is the cause of cancer. (By the way tar causes cancer by switching off the tumour suppression genes)

Ohh right, Oncogenes, right? But thank you so much

 

[6Astarstudent]

Ohh right, Oncogenes, right? But thank you so much

yup, by switching off tumor suppressor genes the proto-oncogenes are activated turning into oncogenes that proliferate instead of dieing.

 

[Afza Munir]

i need some help here for AS level (11) what is the easy way of learnin about biological molecules?
no matter how many times i study it i dont understand the whole thing

 

[1357911]

Assalamualaikum.
Can sombody helpme with the following question please?
Maiz is a C4 plant. Explain how the structure of the leaves of maize plants enable them to photosyntesize more effectively at high temp than wheat plants?

 

[Afza Munir]

C4 plants almost never saturate with light and under hot, dry conditions much outperform C3 plants. They use a two-stage process were CO2 is fixed in thin-walled mesophyll cells to form a 4-carbon intermediate, typically malate (malic acid). The reaction involves phosphoenol pyruvate (PEP) which fixes CO2 in a reaction catalyzed by PEP-carboxylate. It forms oxaloacetic acid (OAA) which is quickly converted to malic acid. The 4-carbon acid is actively pumped across the cell membrane into a thick-walled bundle sheath cell where it is split to CO2 and a 3-carbon compound.
This CO2 then enters the Calvin cycle in a chloroplast of the bundle sheath cell and produces G3P and subsequently sucrose, starch and other carbohydrates that enter the cells energy transportsystem.

 

[Afza Munir]

what is the difference between ATP and ADP ?
What is there function?

 

[Afza Munir]

any one who needs help and short good notes of any cie subjects just check out this website :http://www.s-cool.co.uk/a-level

 

[Afza Munir]

Re: Stuck in Biology?? Post your doubts here!!

Assalamoalaikum!

Please, help me with this question:
Describe the function of vasa recta.

Mark scheme points:
-removing water;
-from/ reabsorbed by collecting ducts;
-ref. to maintain water potential gradient (in medulla)

Jazakumullah Khair..

Each of the vasa recta has a hairpin turn in the medulla and carries blood at a very slow rate, two factors crucial in the maintenance ofcountercurrent exchange that prevent washout of the concentration gradients established in the renal medulla.[2]
The maintenance of this concentration gradient is one of the components responsible for the kidney's ability to produce concentrated urine.
On the descending portion of the vasa recta, NaCl and urea are reabsorbed into the blood, while water is secreted. On the ascending portion of the vasa recta, NaCl and urea are secreted into the interstitium, while water is reabsorbed. hope this helps you

 

[Afza Munir]

what is fluid mosaic model ?

 

[Eng Minhal]

what is the difference between ATP and ADP ?
What is there function?

ATP is the active energy used by organisms to carry out operation.

ATP has Three- Phosphate groups filled with energy.

ATP utilizes its energy by breaking a Phosphate Bond and forming ADP; The ADP is then again built back to ATP and this cycles carry on. Its a non-stop process taking place inside our bodies.

ADP = Two Phosphate. It can't release/ provide energy like ATP.

 

[Eng Minhal]

what is fluid mosaic model ?

Two Scientists describing Structural features of Biological membranes. They named their model Fluid mosaic cause both the Protein and Phospholipid can about a diffusion.
Parts of membrane move freely and there's fluid.