Question

1. After being produced in the endoplasmic reticulum, some proteins go on to the __________ where they may undergo final modifications before being packaged to be sent along to their final destination inside or outside of the cell.

2. The cell membrane allows some molecules, such as oxygen and carbon dioxide to pass through, while preventing other molecules such as glucose and amino acids from passing through, this means cell membranes are ______________.

Answer 1

1. After being produced in the endoplasmic reticulum, some proteins go on to the Golgi complex where they may undergo final modifications before being packaged to be sent along to their final destination inside or outside of the cell.

Explanation: - Ribosomes present in association with rough endoplasmic reticulum are the actual site for protein synthesis. From the rough endoplasmic reticulum, proteins are transported to the Golgi complex (Golgi apparatus) also known as dictyosome.

- Golgi complex is a stack of membranous cisternae located close to the nucleus of the cell and a maturation site for the synthesized proteins.

- Functions of Golgi apparatus :-

• post translational modifications of proteins

• protein sorting and packaging into secretory vesicles before transporting them to their destination inside or outside of the cell.

• site for incorporation of carbohydrates into newly synthesized proteins to form glycoproteins.

2. The cell membrane allows some molecules such as oxygen and carbon dioxide to pass through, while preventing other molecules such as glucose and amino acids from passing through, this means cell membranes are selectively permeable (semipermeable).

Explanation:-

- Cell membrane is a semipermeable (selectively permeable) lipid bilayer that contains protein molecules in between. It consists of 50% proteins, 45% lipids and 5% carbohydrates.

- Cell membrane lipids are amphipathic molecules (both hydrophilic and hydrophobic) i.e. their head/polar region is hydrophilic and tail/non polar region is hydrophobic. These lipids are arranged such that the tail ends are directed towards the center of the membrane whereas the head ends are directed towards the extra cellular fluid (on the outside) and cytoplasm (on the inside).

- Cell membrane acts as a selectively permeable membrane as it allows the passage of fat soluble (lipophilic or hydrophobic) molecules like oxygen, carbon dioxide, alcohol, fatty acids across the cell membrane while preventing the passage of water soluble (hydrophilic or lipophobic) molecules like urea, glucose, amino acids.