Plant Cell Review

Components of cytoplasm

cytosol, cell organelles, cytoskeleten (microtubules, microfilaments, and intermediate filaments), cell inclusions (ergastic components)

Photosynthesis stages and localisations

Light-dependent reactions: thylakoid membranes of chloroplasts
(produces ATP, NADPH, and molecular oxygen)
Light-independent reactions (Calvin Cycle): stroma of chloroplasts (CO2 is fixed by RuBisCo and reduced by ATP/NADPH; produced carbohydrates in the form of glucose)

Cell wall modifications of angiosperm plants

Lignification: deposition of lignin in secondary cell walls
Suberization: deposition of suberin to make cell walls impermeable to gas exchange
Cutinization: formation of waxy cuticle on epidermal cells (e.g. leaves), protecting from water loss
Mineralization: deposition of inorganic substances to enhance mechanical strength

Pits and plasmodesmata allow for water transport and communication between cells

Nucleolus origin

Forms around nucleolar organizer regions which contain genes for ribosomal RNA (present during interphase as it disassembles during mitosis)

Nucleolus structure

Fibrillar centers: contain rRNA genes

Dense fibrillar component: where rRNA transcription and processing occurs
Granular component: responsible for ribosomal subunit assembly

Nucleolus functions

Synthesizes and process rRNA, assembles ribosomal subunits and regulates the cell cycle/stress responses

Pathways of genetic information flow

DNA replication: semiconservative process that results in the production of two identical DNA strands
Transcription: DNA is transcripted into mRNA by RNA polymerase in the nucleus
Translation: mRNA is translated into proteins via complementary tRNA codons that code for specific amino acids, forming a polypeptide chain

Chemical composition of primary cell wall of angiosperm plants

Cellulose: linear beta- 1,4-glucan chains
Hemicelluloses- xyloglucans that cross-link cellulose microfibrils

Pectins- homogalcturonan and rhamnogalacturonans (responsible for wall hydration, porosity, and plasticity)
Cell wall proteins
Water

Structure of biological membranes

Phosopholipid bilayer, proteins (integral, peripheral), sterols, carbohydrates (bind to proteins/lipids to form glycoproteins/glycolipids)

Function of biological membranes

Separation of the cell and organelles from environment

Regulate what is transported into the cell (selective permeability/regulated transport)
Compartmentalization of metabolic processes
Anchoring of enzymes/protein complexes
Signal reception/transduction
Cell-cell interaction/communication

Vacuole origin

E.R. and Golgi apparatus

Vacuole structure

surrounded by a single membrane: tonoplast

Filled with cell sap (ions, sugars, enzymes, pigments)

Vacuole functions

Maintains turgor pressure
Stores nutrients, metabolites, pigments
Detoxification and sequestration of harmful compounds (keeping harmful compounds from the cytoplasm)
Regulates pH and ion homeostasis for cytoplasm

Participates in intracellular digestion

Types of membrane transport pathways

Passive transport, active transport, endocytosis (pinocytosis “drinking”, phagocytosis “eating”, receptor-mediated endocytosis), exocytosis

Endoplasmic reticulum organisation

Rough endoplasmic reticulum: covered with ribosomes on its cytosolic
Smooth endoplasmic reticulum: lacks ribosomes and has a tubular structure

Endoplasmic reticulum functions

RER: synthesis of membrane, secretory and lysosomal proteins, initial folding and quality control of proteins, N-glycosylation of newly synthesized proteins
SER: synthesis of lipids, phospholipids, and sterols
Detoxification of xenobiotics
Calcium ion storage and regulation
In plant cells: synthesis of membrane lipids and precursors of cell wall components

C3 plants

First stable product: 3-phosphoglycerate (3C)

CO₂ fixation by RuBisCO in mesophyll cells

No spatial separation of processes

High rate of photorespiration

Typical of temperate climate plants (e.g. wheat, rice)

C4 plants

First stable product: oxaloacetate (4C)

CO₂ initially fixed by PEP carboxylase

Spatial separation:

mesophyll cells – CO₂ fixation

bundle sheath cells – Calvin cycle

Reduced photorespiration

Typical of tropical plants (e.g. maize, sugarcane)

C3 and C4 photosynthesis comparison

C4 photosynthesis is more efficient under high light intensity, high temperature and low CO₂ concentration, while C3 photosynthesis is energetically less demanding.

Golgi apparatus organization

Composed of flattened membrane sacs called cisternae

cis-Golgi (receiving side)

medial cisternae

trans-Golgi and trans-Golgi network (TGN) (sorting and exporting side)

Vesicles transport materials between ER and Golgi

Golgi apparatus functions

Post-translational modification of proteins (glycosylation)

Sorting and targeting of proteins to correct destinations

Synthesis of cell wall polysaccharides (pectins, hemicelluloses) in plant cells

Formation of secretory vesicles

Participation in membrane renewal

The Golgi apparatus plays a key role in secretion and intracellular trafficking.