Hi Thaheera, thanks for commenting! The beta pleated sheet is a type of secondary structure of proteins (the other type being the alpha helix).
It involves the formation of INTRAmolecular HYDROGEN bonds between the O atom of C=O group of one amino acid, and the H atom of N-H group of another amino acid. Only atoms of the polypeptide BACKBONE are involved in the formation of hydrogen bonds(i.e. R groups are not involved). Since the hydrogen bonds formed here are INTRAmolecular (ie. not intermolecular), the beta pleated sheet is made up of only ONE polypeptide chain .
In a beta-pleated sheet, the beta strands that make up one sheet can run in parallel or antiparallel directions. However, they are still part of the same one polypeptide chain. Ill be posting up a picture in my next post to give you a visual on this.
Hope this clears it up! Let me know if you have further queries! :)
Hi Thaheera, a nucleotide is a general term used to describe monomers making up polynucleotides/ nucleic acids. A nucleotide is made up of a pentose sugar (either ribose or deoxyribose), a nitrogenous base, and one phosphate group. Ribonucleotide is a more specific term describing nucleotides where the pentose sugar is ribose (ie. in RNA), whereas deoxyribonucleotides are nucleotides where the pentose sugar is deoxyribose (ie. in DNA). Hope that this is clear!
Hi Miss Teong :D i want to ask some questions on Phospholipids :D 1. Does the hydrophilic head allow polar molecules and non-polar molecules to pass through or only polar molecules? 2. In the cell membrane, are the phospholipids always arranged with the hydrophilic head facing outwards and hydrophobic tails facing inwards, or does it depends on the type of environtment the cell is in? 3. According the page 17 of biological molecules (part 1) lecture notes, under the functions of phospholipids, it states that 'it regulates the type of molecule entering or leaving the cell, as the hydrophobic tail allows only lipid-soluble/non-polar molecules to pass through the cell membrane'. If the hydrophilic head is facing outwards, and if it only allows polar molecules to pass through, how does the non-polar molecules pass through the hydrophilic head?
1 and 2. Phospholipids are amphipathic with a hydrophilic ("water-loving") phosphate head and hydrophobic ("water-fearing") fatty acid tails. When phospholipids are placed in an aqueous environment (like inside our bodies), they will aggregate to form the bilayer like that of cell membranes in our bodies (with heads facing outwards and tails facing inwards). However, when placed in a hydrophobic environment instead, I would think that the phospholipids would be oriented in an opposite direction with the tails facing outwards and the heads facing inwards. In other words, the orientation of phospholipid aggregates are dependent on the environment.
In cell membranes, the structure of phospholipids is responsible for the semi-permeability of membranes. Because the interior of the phospholipid bilayer is occupied by hydrophobic fatty acid chains, the membrane is impermeable to polar and charged (eg. ions) molecules. Hence, only nonpolar and uncharged molecules can pass through the cell membrane. However, note that size is also a factor in determining whether it is able to pass through the cell membrane. Smaller molecules can pass through the cell membrane easier than larger molecules.
3. I think you should be able to find out how polar molecules are able to pass through the cell membrane when you do your SDL component for this topic on membranes. :)
Hi:-)
ReplyDeleteIs a beta pleated sheet made up of one polypeptide chain or a few polypeptide chains? Please clarify.
Thanks:-)
~Thaheera
Hi Thaheera, thanks for commenting! The beta pleated sheet is a type of secondary structure of proteins (the other type being the alpha helix).
ReplyDeleteIt involves the formation of INTRAmolecular HYDROGEN bonds between the O atom of C=O group of one amino acid, and the H atom of N-H group of another amino acid. Only atoms of the polypeptide BACKBONE are involved in the formation of hydrogen bonds(i.e. R groups are not involved). Since the hydrogen bonds formed here are INTRAmolecular (ie. not intermolecular), the beta pleated sheet is made up of only ONE polypeptide chain .
In a beta-pleated sheet, the beta strands that make up one sheet can run in parallel or antiparallel directions. However, they are still part of the same one polypeptide chain. Ill be posting up a picture in my next post to give you a visual on this.
Hope this clears it up! Let me know if you have further queries! :)
Thanks:-)
DeleteHi:-)
ReplyDeleteThaheera here.. The basic unit of dna- is it called a deoxyribonucleotide, or just a nucleotide?
Thx:-)
Hi Thaheera, a nucleotide is a general term used to describe monomers making up polynucleotides/ nucleic acids. A nucleotide is made up of a pentose sugar (either ribose or deoxyribose), a nitrogenous base, and one phosphate group. Ribonucleotide is a more specific term describing nucleotides where the pentose sugar is ribose (ie. in RNA), whereas deoxyribonucleotides are nucleotides where the pentose sugar is deoxyribose (ie. in DNA). Hope that this is clear!
ReplyDeleteHi Miss Teong :D i want to ask some questions on Phospholipids :D 1. Does the hydrophilic head allow polar molecules and non-polar molecules to pass through or only polar molecules? 2. In the cell membrane, are the phospholipids always arranged with the hydrophilic head facing outwards and hydrophobic tails facing inwards, or does it depends on the type of environtment the cell is in? 3. According the page 17 of biological molecules (part 1) lecture notes, under the functions of phospholipids, it states that 'it regulates the type of molecule entering or leaving the cell, as the hydrophobic tail allows only lipid-soluble/non-polar molecules to pass through the cell membrane'. If the hydrophilic head is facing outwards, and if it only allows polar molecules to pass through, how does the non-polar molecules pass through the hydrophilic head?
ReplyDeleteHi Jacquelyn,
Delete1 and 2. Phospholipids are amphipathic with a hydrophilic ("water-loving") phosphate head and hydrophobic ("water-fearing") fatty acid tails. When phospholipids are placed in an aqueous environment (like inside our bodies), they will aggregate to form the bilayer like that of cell membranes in our bodies (with heads facing outwards and tails facing inwards). However, when placed in a hydrophobic environment instead, I would think that the phospholipids would be oriented in an opposite direction with the tails facing outwards and the heads facing inwards. In other words, the orientation of phospholipid aggregates are dependent on the environment.
In cell membranes, the structure of phospholipids is responsible for the semi-permeability of membranes. Because the interior of the phospholipid bilayer is occupied by hydrophobic fatty acid chains, the membrane is impermeable to polar and charged (eg. ions) molecules. Hence, only nonpolar and uncharged molecules can pass through the cell membrane. However, note that size is also a factor in determining whether it is able to pass through the cell membrane. Smaller molecules can pass through the cell membrane easier than larger molecules.
3. I think you should be able to find out how polar molecules are able to pass through the cell membrane when you do your SDL component for this topic on membranes. :)