A level Biology: Post your doubts here!

[rogue94]

which year is this?

Q1. (a) (ii).........
http://www.xtremepapers.com/papers/...nd AS Level/Biology (9700)/9700_w10_qp_23.pdf

 

[hihi]

DNA and RNA are polynucleotides ,made up of long chains of nucleotides.A nucleotide consists of a pentose sugar,a phosphate group and an nitrogen-containing base

.A DNA molecule consists of two polynucleotide chains ,linked by hydrogen bonds between the bases.Adenine always bonds with thymine and cytosine with guanine
.RNA which comes in several different forms , has only one polynucleotide chain ,although this may be twisted back onto itself like in tRNA .In RNA the base thymine is replaced by uracil.

DNA molecules replicate during interphase .The hydrogen bonds between the bases break ,allowing free nucleotides to fall into position beside their complementary bases on each strand of the original DNA molecule .Adjacent nucleotides are then linked ,through their phosphates and sugars ,to form new strands .Two complete new molecules are thus formed from one old one ,each new molecule containing one old strand and one new .

The sequence of bases on a DNA code for a amino acids in a protein (or polypeptide) .Each amino acid is coded for by three bases .A length of DNA coding for one complete protein or polypeptide is a gene.

During protein synthesis , a complementary copy of the base sequence on a gene is made by building a molecule of mRNA against one DNA strand .The mRNA then moves to a ribosome in the cytoplasm.
tRNA molecules with complementary triplets of bases temporarily pair up with the base triplets on the mRNA ,bringing appropriate amino acids .As two amino acids are held side by side ,a peptide bond is formed between them .The ribosome moves along the mRNA molecule , so that appropriate amino acids are linked together , following the sequence laid down by the base sequence on the mRNA

That should pretty much sum up the whole chapter .Hope this helps!

Thank you soooo much !!! I wish u a good luck on the exam !

 

[KurayamiKimmi]

Thank you soooo much !!! I wish u a good luck on the exam !

thanks!!! ^_^

 

[geek101]

yup kay tx a lot...

oh i wrote potential difference somewhere there...ignore that, physics and bio are taking over me

 

[confused_soul]

heyy can sum 1please explain me what happens in DNA synthesis after replication occurs in DNA ? ribosomes carry den out n all wat is role of tRNA ? n wats translation

 

[angelpari]

heyy can sum 1please explain me what happens in DNA synthesis after replication occurs in DNA ? ribosomes carry den out n all wat is role of tRNA ? n wats translation

u need PROTEIN SYNTHESIS..???

 

[soccerprinc3]

Can someone please explain the full process of an immune response? as in the order of how everything happens and which cells reach the pathogen first?

 

[raamish]

Hey guys help: name a part of the human body where B-cells are produced by division of stem cells?

State two similarities and one difference b/w the structure of ribose and the structure of B- glucose?

 

[angelpari]

heyy can sum 1please explain me what happens in DNA synthesis after replication occurs in DNA ? ribosomes carry den out n all wat is role of tRNA ? n wats translation

Translation is a step in protein synthesis when the genetic code carried by mRNA is decoded to produce the specific sequence of amino acids in polypeptide chain. The process follows transcription in which DNA sequence is copied into mRNA..

PROTEIN SYNTHESIS..
In the nucleus, part of DNA unwinds and unzips as the hydrogen bonds between the bases break. Free activated RNA nucleotides pair up with the exposed bases of one strand only.
In the cytoplasm, there are free amino acids and tRNA molecules. At one end of each tRNA molecule is a site to which an amino acid can bind. At the other end are three unpaird bases. The base triplet is called an anticodon. Each tRNA molecules binds with the particular amino acid, under the control of specific enzyme and with energy from ATP.
Meanwhile, also in the cytoplasm, the mRNA molecule attaches to a ribosome. Ribosone are made of ribosomal RNA and proteins and contain a large and small subunit. Six bases at a time are exposed to the large subunit, tRNA molecules with the anticodon forms hydrogen bonds with the codon. The tRNA molecules has the amino acids attach to it.
A second tRNA molecules bonds with the next three exposed bases. This one brings a different amino acid. The two amino acids are held closely together and a peptide bond is formed between them. The raection is catalysed by the enzym peptidyl tranferase, which is found in the small subunit of the ribosome.
The ribosomes now move along the mRNA 'reading' the next three bases of the ribosome. A third tRNA molecules brings a third amino acid, which joins to the second one. The first tRNA leave.
The polypeptide chain continues to grow until a stop codon is exposed on the ribosomes.


i hope this make some sense.. do correct me where m wrong..

 

[SalamH]

PPL ANY ONE DOING BIO VARIANT 21 . ANY ONE KNOWS WHEN IS IT PLS ANS MY QUES CUZ I WANNA GUESS P22 WHICH IS 2MORO

 

[Gémeaux]

-In an antibody, does the sugar chain attached influence the specificity of the antibody?
-What are the exact definitions for *nitrification* and *nitrogen fixation*?
Please help

 

[rogue94]

Hey guys help: name a part of the human body where B-cells are produced by division of stem cells?

State two similarities and one difference b/w the structure of ribose and the structure of B- glucose?

part of body: bone marrow
similarities: in both structures the H atom is below C atom 1 or OH is above C 1 atom in ring structures of both ribose glucose. Also, the H and OH are at same place on C atom 2.
differences: B-glucose has 6 C atoms while ribose has 5 C atoms or B-glucose is 6-membered ring while ribose is 5-membered ring.

 

[eyamwir]

alveolar wall is one cell thick and it is a squamous epithelium but capillary wall is one cell thick and it is not a squamous epithelium, why? can anyone explain? and what is squamous epithelium? i don't get it

 

[trgirl]

Because the person has memory B lymphocytes in his bloodstream. When a pathogen with the same/similar antigen invades the body a secondary immune response will be triggered and the B lymphocytes will undergo mitosis to form plasma cells. These plasma cells will then produce antibodies specific to the antigen which will then destroy the invading cells.

thank uuuu

 

[rogue94]

alveolar wall is one cell thick and it is a squamous epithelium but capillary wall is one cell thick and it is not a squamous epithelium, why? can anyone explain? and what is squamous epithelium? i don't get it

capillary wall is squamous endothelium (difference of epithelium and endothelium). Squamous cells or squames are flat cells, which are long and thin. Hence, squamous endothelial/epithelial cells form squamous endothelium/epithelium. Capillary endothelium is 1-2 um thick while alveolar epithelium is 0.5 um think.

 

[raamish]

part of body: bone marrow
similarities: in both structures the H atom is below C atom 1 or OH is above C 1 atom in ring structures of both ribose glucose. Also, the H and OH are at same place on C atom 2.
differences: B-glucose has 6 C atoms while ribose has 5 C atoms or B-glucose is 6-membered ring while ribose is 5-membered ring.

ty stem cells are cells of the marrow rite?

 

[Soldier313]

oh i wrote potential difference somewhere there...ignore that, physics and bio are taking over me

lol no p......i totally understand

 

[eyamwir]

capillary wall is squamous endothelium (difference of epithelium and endothelium). Squamous cells or squames are flat cells, which are long and thin. Hence, squamous endothelial/epithelial cells form squamous endothelium/epithelium. Capillary endothelium is 1-2 um thick while alveolar epithelium is 0.5 um think.

so are epithelium and endothelium the same? what are the difference?

 

[rogue94]

ty stem cells are cells of the marrow rite?

yeah!

 

[eyamwir]

what does carcinogen do?