Stroma, matrix

Chloroplasts of higher plants are saucer-shaped, and from 4 to 10 ym in diameter and 1 to 3 ym thick. The chlorophyll is concentrated in bodies within the chloroplasts called grana, which are about 0.4 ym in diameter. Under the electron microscope, the grana appear as highly organized, precisely stacked lamellae, to which the chlorophyll is bound, imbedded in a stroma matrix. The light and associated electron transport reactions take place in the lamellae, whereas enzymes involved in carbon dioxide fixation are located in the stroma. 

Stroma, matrix colorless, homogeneous (by light microscopy) ground substance of cell organelles, like Chloroplasts (see) and Mitochondria (see). 

Edwards, A., M.R. Prausnitz. 1998. Fiber matrix model of sclera and corneal stroma for drug delivery to the eye. AIChE Journal 41 214. 

FIGURE 1. Thin section of part of an isolated chloroplast showing the internal thylakoid membrane system which consists of appressed grana lamellae (g) and non-appressed stroma lamellae (s) embedded in the stroma protein matrix and surrounded by a double membrane envelope (e). 

A large part of the biosynthetic capacity of a plant cell is localized in plastids, which are self-replicating organelles surrounded by a doublemembrane envelope. Plastids are present in most cells of photosynthetic eukaryotes. In most angiosperms, however, sperm cells lack plastids, a fact that makes plastid inheritance solely maternal. The envelope is composed of an outer and inner membranes, which differ in their permeability, separated by a 10 to 20-nm gap. The plastids contain DNA that is concentrated in a section of the stroma, which is the background matrix of the plastid. The plastidial ribosomes are smaller that the cytoplasmic ribosomes. 

Figure 19.25. Comparison of Photosynthesis and Oxidative Phosphorylation. The light-induced electron transfer in photosynthesis drives protons into the thylakoid lumen. The excess protons flow out of the lumen through ATP synthase to generate ATP in the stroma. In oxidative phosphorylation, electron flow down the electron-transport chain pumps protons out of the mitochondrial matrix. Excess protons from the intermembrane space flow into the matrix through ATP synthase to generate ATP in the matrix.

Key factors in the complex process of invasion and metastasis are proteolysis of the local connective tissue stroma and locomotion into the region of the matrix modified by proteolysis. 

Figure 2.5 compares the orientation of the ATP synthase F0/Fj complex in mitochondria with that in chloroplasts. The lumen enclosed by the thylakoid membrane is slightly acidic it corresponds to the mitochondrial intermembrane space where electron transport first pumps protons (H+). In chloroplasts, ATP is made as protons diffuse from the thylakoid lumen through the membrane to the chloroplast stroma (Fig. 2.4). In mitochondria, ATP is made as protons diffuse from the mitochondrial intermembrane space through the inner mitochondrial membrane to the mitochondrial lumen or matrix.

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