Lecture 3 & 4 Cell Organelles: Structure-Function Relationships Flashcards
What are cells? What are cells made of?
- Small units bound by a plasma membrane (or cell wall)
- Contain aqueous fluid (cytosol) plus:
- chemicals (cytoplasm)
- structural support (cytoskeleton)
- membrane bound organelless
What kind of membrane surrounds cells?
• All cells are surrounded by a plasma membrane
• Single membrane (lipid bilayer)
• Membrane is selectively permeable;
IntraCellular Fluid (ICF) (cytosolic face) ≠ ExtraCellular Fluid (ECF) (non-cytosolic face)
What is the plasma membrane made of?
- Plasma membrane = complex of:
- Lipids (amphipathic)
- Proteins
- Carbohydrates (CnH2nOn)
- Glycolipids
- Glycoproteins
- Peptidoglycans
- Glycosaminoglycans
Why is the Plasma Membrane Selectively Permeable?
• Because lipids are amphipathic (Ampithatic both hydrophilic and hydrophobic)
- hydrophobic core (hydrophobic lipid tails)
- hydrophilic exterior (hydrophilic phosphate heads)
What is the selectively permeable model called and what does it entail?
- Fluid mosaic model:
- Integral & peripheral membrane proteins
- Transport hydrophilic solutes
What is the cell wall?
- Plant cells and bacteria have a cell wall surrounding the plasma membrane
- Further limits passage of molecules in to / out of the cell
What is the cell wall in plant?
- Plant cell walls composed of cellulose
- Complex carbohydrate
- Has to be digested by cellulase (which animals don’t have!)
What is the cell wall in bacteria?
- Bacterial cell walls composed of peptidoglycans
- Can be surrounded by gelatinous polysaccharide layer:
- capsule
- glycocalyx
- “slime layer”
What is an experiment with which we can test the cell wall in bacteria?
- Can stain bacteria with Gram’s Stain
- Gram positive bacteria: thick peptidoglycan layer to cell wall prevents stain being washed out (means cell wall exists)
- Gram negative bacteria: peptidoglycan layer to cell wall allows gram stain to be washed out (no cell wall)
What are the Cell Surface Appendages?
- Plasma membrane and/or cell wall can have:
- villi / microvilli
- cilia
- flagella
Why do Cell Surface Appendages exist?
- To move the cell (flagella / cilia)
- To move ECF (cilia)
- To increase the cell’s surface area (villi / microvilli)
What is the function of the nucleus?
- Nucleolus-site of ribosomal synthesis
-Contains chromosomes the cells blue-print for proteins – DNA
+ In dividing cells the DNA is replicated
• Mitosis
-Chromosomes composed of condensed chromatin
-Chromatin = DNA + histone proteins
What is DNA used for in non-dividing cells?
• In non-dividing cell, use DNA blueprint for protein synthesis:
+Two step process:
-Transcription of DNA to RNA (in nucleus)
-Translation of RNA to protein (in rough endoplasmic reticulum)
How are the Nucleus and Nucleolus separated from the cytoplasm?
- Double membrane (nuclear envelope) around nucleus with nuclear pores
- No membrane around nucleolus
What are centrioles?
- Only found adjacent to nucleus in animal cells
- Perpendicular pair of specialist microtubules
- Organise mitotic (or meiotic) spindle
What is the mitochondrial structure?
- Bounded by double membrane
- Inner and outer mitochondrial membranes separated by aqueous intermembrane space
- Inner mitochondrial membrane (IMM) convoluted into cristae (larger surface area for citric acid cycle=makes ATP)
- Inside IMM is the mitochondrial matrix
- Mitochondrion has its own mit.DNA
What is the mitochondrial function?
• Mitochondrion contains series of oxidative enzymes
• Catalyse aerobic catabolism of fuels (carbohydrates, fatty acids and amino acids / proteins)
• Harness energy as ATP
=
• Mitochondria harness energy from C-based fuels by oxidative phosphorylation
• Generate and metabolise reactive oxygen species (ROS) and free radicals
• Mediate apoptosis
What happens in the ICF (intracellular fluid)(cytosolic face)?
-Anaerobic carbohydrate metabolism (glycolysis) (first step but outside mitochondria)
-Aerobic oxidation of carbohydrates, lipids and amino-acids (β-oxidation and Kreb’s/TCA cycle)
-Phosphorylation of ADP to ATP
• Oxidative metabolism of glucose
• Harness energy as ATP:
C6H12O6 + 6O2 = 6CO2 + 6H2O+ ATP
What are the synthetic organelles?
- Chloroplasts – photosynthesis
- Ribosomes – translation of proteins
- Endoplasmic reticulum – protein and lipid synthesis
- Golgi apparatus – protein processing, sorting & secretion
What is a chloroplast and what does it do?
• Only found in photosynthetic cells
• Catalyse anabolic (rather than catabolic) metabolism
• Harness light energy in photosynthesis:
Energy + 6CO2 + 6H2O = C6H12O6 + 6O2
• Bounded by double membrane
• Has its own DNA
What are ribosomes?
- In nucleus (nucleolus), DNA is transcribed into RNA:
- Messenger (m)RNA
- Ribosomal (r)RNA
- Transfer (t)RNAs
- mRNA code is translated into amino-acid sequence (peptide / protein) by ribosomes
What is the structure of ribosomes?
• Ribosomes have 2 subunits: small and large • Each subunit is a complex of: • rRNA • proteins • Which component is enzymatic? = rRNA! -Prokaryotes = 70S ribosomes -Prokaryotes = 80S ribosomes \+can be exploited with antibiotics (only target 70S)
What are polysomes?
• Several ribosomes translating the same mRNA template
What is the endoplasmic reticulum?
• Continuous, highly convoluted membrane system – nucleus to plasma membrane
What is the path travelled by proteins for secretion by the cell?
Endoplasmic Reticulum (ER) = Golgi Apparatus = Secretory Vesicles
What is the difference between Smooth vs Rough Endoplasmic Reticulum?
• Ribosomes!:
- smooth - no ribosomes
- rough - bound ribosomes
What does the rough endoplasmic reticulum do?/What is its function?
-Rough ER makes membrane and organelle proteins and virtually all proteins secreted by the cell:
• protein synthesis, transport and sorting
• ribosomes protein synthesis translate RNA into protein
• proteins made by the bound ribosomes cross the rough ER membrane
• proteins folded and modified in ER
• Have sugars added glycosylation to protect proteins
What are the other differences/similarities between Smooth vs Rough Endoplasmic Reticulum?
- Smooth ER – site of lipid synthesis
- Rough ER – site of protein synthesis (translation)
- Synthesis generally occurs in lumen of the cisternae (for both)
What is the Golgi apparatus and what does it do?
• Series of specialised, stacked cisternae through which proteins (and lipids) are processed prior to:
• insertion into plasma membrane
• secretion
• Molecules enter on cis face and exit from trans face of GA – move via vesicular trafficking
+ Enzymes in Golgi can add carbohydrate:
• carbohydrate + lipid = glycolipid
• carbohydrate + protein = glycoprotein
• Golgi Apparatus “sorts” molecules for final destination
What is a vesicle?
- “Small”, spherical, sealed, single membrane (lipid bilayer) contains ICF
- Not a micelle! (SOS)
What is vesicular trafficking?
- Vesicle buds off from one membrane (cisterna)
- Vesicle passes through the cytoplasm and fuses with another membrane
- Traffics luminal and membrane content of vesicle
What are the secretory pathways?
-Two types:
• Exocytosis- constitutive i.e. not regulated e.g. Extra cellular matrix proteins by fibroblasts
• Secretory vesicles-regulated by signals e.g. Insulin-b cells in islets of Langerhans
What are the digestive organelles?
- Endosomes
- Lysosomes
- Peroxisomes
What is an endosome?
• Incoming vesicle formed by endocytosis
• Buds off from plasma membrane
• Pinocytosis
• Phagocytosis
• 3 types: early, recycling and late endosome (EE, RE & LE)
-EE first one to form/ forms from endocytosis then becomes:
-RE for exocytosis or
-LE for lysosomal pathway or golgi apparatus
What is a lysosome?
- Late endosome fuses with vesicle containing “lysozymes” (acid hydrolyases)
- At low pH, hydrolyse chemical bonds to degrade contents of lysosome
What is a peroxisome?
• Contain peroxidase enzymes: RH2 + O2 → R + H2O2 (HOOH) • Also contain catalase enzyme: RH2 + H2O2 → 2 x H2O • Initial catabolism of long chain FA, branched chain FA, amino acids and polyamines
What are prokaryotes and eukaryotes?
- Historical (antiquated) terms
- “Karyon” = “nut / kernel” (nucleus surrounded by double membrane / nuclear envelope)
- Prokaryotes – don’t have a nucleus; “before the nucleus”
- Eukaryotes – cells with nucleus
Do Prokaryotic and eukaryotic cells simply
differ with respect to having a nucleus?
-FALSE
• Absence vs presence of ANY membrane bound organelles
(i.e. nucleus, mitochondria, Golgi apparatus, etc.)
How else does a prokaryote differ from a eukaryote?
-A prokaryote has:
• Relatively simple internal structure; only common organelle = ribosome
• Nucleoid = bacterial chromosome: single circular molecule of “naked” DNA (no histones)
• Metabolism occurs in cytosol (no ER or mitochondria)
“Cells are either prokaryotic or
eukaryotic” - True or False?
-FALSE
• Classification refers to organisms not cells - Prokaryota vs Eukaryota
“Prokaryotes are simple; eukaryotes are
complex” - True or False?
-FALSE
• 5 kingdoms of eukaryotes
• 2 kingdoms of prokaryotes but each with multiple phyla
What are the Eukaryote kingdoms?
- Eukarya: \+ Multicellular: • Animals • Plants • Fungi \+ Unicellular: • Yeast • Amoeba
What are the Prokaryote kingdoms?
- Prokarya: \+ Bacteria: • Gram positive vs gram negative • >12 phyla \+ Archaea: • Euryarchaeota vs Crenarchaeota • >6 phyla
What are the prokaryote morphologies?
4 morphologies:
1) Cocci (spherical
(2) Bacillus (rods/rod-like)
(3) Spirochetes (spiral)
(4) Vibrio (“commas”/curved rods)
“Prokaryotes are unicellular; eukaryotes
are multicellular” - T/F?
-FALSE
• Some prokaryotes can be multicellular at specific stages of their life cycle
• Some eukaryotes are unicellular
-Prokaryotes:
• Archaea always unicellular
• Bacteria usually unicellular (e.g. E.coli, Pseudomonas & Streptococcus)
• Some bacteria have multicellular stages (e.g. myxobacteria) or form
colonies (e.g. cyanobacteria)
Do all eukaryotic cells have nuclei?
- All mammals – mature erythrocytes lack nuclei
- Most non-mammalian vertebrates have nucleated red blood cells
- “Lens fibre” cells in the eye have no nuclei
Do all cells have the same number/type of mitochondria?
-NO
+eg.: Hepatocytes have c.2,000 mitochondria per cell (accounting for 20% of cell volume) - Why?
= perform most of the livers function = need lots of ATP
• Unicellular organisms usually have a single mitochondrion
• Erythrocytes and some unicellular eukaryotes* have zero mitochondria *(microsporidians, metamonads & archamoebae)
+implies they have no need/less need for ATP
• Mature “lens fibre” cells (long, thin cells which comprise the lens) of the eye have:
• No nuclei
• No mitochondria
• No endoplasmic reticulum
How would you expect the number of mitochondria in the midpiece of the sperm to relate to fertility?
- Sperm contain spiral mitochondria wrapped around flaggelum (midpiece)
- mitochondria provides energy for flagellum to move, acrosome (head) no need for energy as soon as it enters the ovary
Which cells should contain the most abundant golgi apparatus?
- Specialised secretory cells!
- need for lots of packing for secretion
