Integral University Assignment: Chloroplast Structure & Function PDF

# Integral University Assignment **Introduction to cell biology and genetics (103)** ## Structure and function of chloroplast **Submitted By:** Nasrin Khatoon **Submitted To:** Durdana Yasir **Name:** Nasrin Khatoon **Branch:** BSc (Hons) Biotechnology **Year/Sem:** 1year/ 1 semester **Enroll No...

# Integral University Assignment **Introduction to cell biology and genetics (103)** ## Structure and function of chloroplast **Submitted By:** Nasrin Khatoon **Submitted To:** Durdana Yasir **Name:** Nasrin Khatoon **Branch:** BSc (Hons) Biotechnology **Year/Sem:** 1year/ 1 semester **Enroll No:** 2400103831 ## Chloroplast - The term chloroplast was first described by Nehemiah Grew and Antonie van Leeuwenhoek - These are a green colored plastid. It contains chlorophyll pigment - They are usually situated near the surface of the cell. - Chloroplast has its own DNA and can reproduce independently from the rest of the cell. They also produce amino acid and lipids required for the production of chloroplast membrane. - These are found in the guard cells located in the leaves of the plants. - This cell organelle is not present in animal cells. - Chloroplasts are present in plant and other eukaryotic organisms that conduct photosynthesis. ## Outer membrane - The outer membrane is made up of a phospholipid bilayer, similar to the cell membrane, which helps maintain the integrity of the chloroplast. - It is permeable to small molecules, ions, and metabolites due to the presence of protein channels called porins, allowing for selective transport. - The outer membrane encases the chloroplast, separating it from the surrounding cytoplasm, thus providing a distinct environment for chloroplast functions. - While photosynthesis primarily occurs within the thylakoid membranes, the outer membrane's role in metabolite transport is essential for efficient photosynthetic activity. - Provide structural support to the chloroplast, maintaining its shape and integrity. ## Inner membrane - The inner membrane is a lipid bilayer, similar to other biological membranes, composed primarily of phospholipids. - It is less permeable than the outer membrane, allowing selective transport of molecules. - The inner membrane is involved in the process of chloroplast division, ensuring the proper distribution of organelles during cell division. - The inner membrane helps maintain an acidic environment within the thylakoid lumen, which is vital for ATP production. ## Thylakoids - The thylakoids consist of flattened and closed vesicles arranged as a membranous network. It may be stacked like coins forming grana. - It may be 40-80 grana in the matrix of a chloroplast - Thylakoids include light-absorbing pigments, a complex chain of electron carriers, and an ATP synthesizing apparatus. - Light reaction occurs in thylakoid membrane. ## Stroma - The stroma is a gel-like fluid that fills the space between the thylakoid membrane within the chloroplast. - The stroma contains ribosomes, allowing for local protein synthesis. - The stroma is involved in various metabolic pathways. - It is a colourless, alkaline, aqueous, protein-rich fluid present within the inner membrane of the chloroplast present surrounding the grana. - The stroma is the site of CO2 fixation and where the synthesis of sugar, starch, fatty acid and some proteins occurs. ## Granum - A granum consists of multiple stacked thylakoids, resembling a stack of pancakes. - Granum is found within the chloroplast of plant cells, specifically in the stroma. - The primary role of granum is to facilitate the light-dependent reactions of photosynthesis. - Light absorption in granum creates a proton gradient used to synthesize ATP. - The number of thylakoids in a granum can vary based on light conditions and plant species. - Granum enables efficient transfer of absorbed light energy to the photosystem. ## Chloroplast DNA - Chloroplast DNA (cpDNA) is also known as plastid DNA (ptDNA). - This is circular double-stranded DNA molecules. - Chloroplast genome size is about 120-217 Kb. - It contains non-coding sequences. ## Function - The main function of chloroplast is photosynthesis. - Process of photosynthesis consists of the following two steps. - Light reaction: Excited chlorophyll molecules - Dark reaction: - Stage 1: Fixation - Stage 2: Reduction - Stage 3: Regeneration of acceptor - Light reaction: It is also known as Hill reaction, photosynthetic electron transfer reaction or photochemical reaction. In light reaction, solar energy is trapped in the form of chemical energy of ATP and NADPH. During this, oxygen is evolved by photolysis. - Dark reaction: It is also known as Calvin cycle, photosynthetic carbon reduction cycle (PCR cycle), carbon fixation reaction or thermochemical reaction. Here, the reducing capacity of NADPH and energy of ATP is utilized for the conversion of CO2 to carbohydrate. It occurs in stroma. - Starch synthesis is occurring within the stroma of chloroplast. - From chloroplast, some of the intermediates are transported to cytosol for sucrose synthesis.