Chapter 1.2 Flashcards
electron micrograph: animal cells
electron micrographs: plant cells
The ultrastructure of an animal cell shows a densely packed cell
Plant cells diagram
Cell surface membrane
-All cells are surrounded by a cell surface membrane which controls the exchange of materials between the internal cell environment and the external environment -The membrane is described as being ‘partially permeable’ -The cell membrane is formed from a phospholipid bilayer of phospholipids spanning a diameter of around 10 nm
Cell wall
-Cell walls are formed outside of the cell membrane and offer structural support to cell -Structural support is provided by the polysaccharide cellulose in plants, and peptidoglycan in most bacterial cells -Narrow threads of cytoplasm (surrounded by a cell membrane) called plasmodesmata connect the cytoplasm of neighbouring plant cells
Nucleus
-Present in all eukaryotic cells, the nucleus is relatively large and separated from the cytoplasm by a double membrane (the nuclear envelope) which has many pores -Nuclear pores are important channels for allowing mRNA and ribosomes to travel out of the nucleus, as well as allowing enzymes (eg. DNA polymerases) and signalling molecules to travel in -The nucleus contains chromatin (the material from which chromosomes are made) -Usually, at least one or more darkly stained regions can be observed – these regions are individually termed ‘nucleolus’ and are the sites of ribosome production
Mitochondria
-The site of aerobic respiration within eukaryotic cells, mitochondria are just visible with a light microscope -Surrounded by double-membrane with the inner membrane folded to form cristae -The matrix formed by the cristae contains enzymes needed for aerobic respiration, producing ATP -Small circular pieces of DNA (mitochondrial DNA) and ribosomes are also found in the matrix (needed for replication)
Chloroplast
-Larger than mitochondria, also surrounded by a double-membrane -Membrane-bound compartments called thylakoids containing chlorophyll stack to form structures called grana -Grana are joined together by lamellae (thin and flat thylakoid membranes) -Chloroplasts are the site of photosynthesis: —-The light-dependent stage takes place in the thylakoids —-The light-independent stage (Calvin Cycle) takes place in the stroma Also contain small circular pieces of DNA and ribosomes used to synthesise proteins needed in chloroplast replication and photosynthesis
Ribosome
-Found freely in the cytoplasm of all cells or as part of the rough endoplasmic reticulum in eukaryotic cells -Each ribosome is a complex of ribosomal RNA (rRNA) and proteins -80S ribosomes (composed of 60S and 40S subunits) are found in eukaryotic cells -70S (composed of 50S and 30S subunits) ribosomes in prokaryotes, mitochondria and chloroplasts -Site of translation (protein synthesis)
Endoplasmic reticulum
Rough Endoplasmic Reticulum (RER) -Surface covered in ribosomes -Formed from continuous folds of membrane continuous with the nuclear envelope -Processes proteins made by the ribosomes Smooth Endoplasmic Reticulum (ER) -Does not have ribosomes on the surface, its function is distinct to the RER -Involved in the production, processing and storage of lipids, carbohydrates and steroids
Golgi apparatus (golgi complex)
-Flattened sacs of membrane similar to the smooth endoplasmic reticulum -Modifies proteins and packages them into vesicles or lysosomes
Large permanent vacuole
-Sac in plant cells surrounded by the tonoplast, selectively permeable membrane -Vacuoles in animal cells are not permanent and small
Vesicle
Membrane-bound sac for transport and storage
Lysosome
-Specialist forms of vesicles which contain hydrolytic enzymes (enzymes that break biological molecules down) -Break down waste materials such as worn-out organelles, used extensively by cells of the immune system and in apoptosis (programmed cell death)
Centriole
-Hollow fibres made of microtubules, two centrioles at right angles to each other form a centrosome, which organises the spindle fibres during cell division -Not found in flowering plants and fungi
Microtubules
-Makes up the cytoskeleton of the cell about 25 nm in diameter -Made of α and β tubulin combined to form dimers, the dimers are then joined into protofilaments. -Thirteen protofilaments in a cylinder make a microtubule -The cytoskeleton is used to provide support and movement of the cell
Microvilli
Cell membrane projections that increase the surface area for absorption
Cilia
-Hair-like projections made from microtubules -Allows the movement of substances over the cell surface
Flagella
-Similar in structure to cilia, made of longer microtubules -Contract to provide cell movement for example in sperm cells
Structure of Animal & Plant Cells which are not found in each other
-The only structures found in animal cells but not plant cells are the centrioles and microvilli -Plant cells also have additional structures: the cellulose cell wall, large permanent vacuoles and chloroplasts
Prokaryotic cells diagram, whatsa present always and sometimes present
The Vital Role of ATP
-All organisms require a constant supply of energy to maintain their cells and stay alive -This energy is required: —-In anabolic reactions – building larger molecules from smaller molecules —-To move substances across the cell membrane (active transport) or to move substances within the cell -In animals, energy is required: —-For muscle contraction – to coordinate movement at the whole-organism level —-In the conduction of nerve impulses, as well as many other cellular processes -In all known forms of life, ATP from respiration is used to transfer energy in all energy-requiring processes in cells -This is why ATP is known as the universal energy currency -Adenosine Triphosphate (ATP) is a nucleotide —-The monomers of DNA and RNA are also nucleotide
Structural Features of Typical Prokaryotic Cells
Prokaryotes have a cellular structure distinct from eukaryotes:
- Their genetic material is not packaged within a membrane-bound nucleus and is usually circular (eukaryotic genetic material is packaged as linear chromosomes)
- Prokaryotes lack membrane-bound organelles
- They are many (100s/1000s) of times smaller than eukaryotic cells
- Their ribosomes are structurally smaller (70 S) in comparison to those found in eukaryotic cells (80 S)
Prokaryotic & eukaryotic cells comparison table
Key Features of Viruses
- Viruses are non-cellular infectious particles that straddle the boundary between ‘living’ and ‘non-living’
- They are relatively simple in structure; much smaller than prokaryotic cells (with diameters between 20 and 300 nm) -Structurally they have: —-A nucleic acid core (their genomes are either DNA or RNA, and can be single or double-stranded)
- A protein coat called a ‘capsid’
- Some viruses have an outer layer called an envelope formed usually from the membrane-phospholipids of a cell they were made in -All viruses are parasitic in that they can only reproduce by infecting living cells and using their protein-building machinery (ribosomes) to produce new viral particles
this is just one example of a virus structure
