Cell Biology Flashcards
Define cell biology
This deals with cell structure, function and cell physiology all at the unit level of a living organism called a cell.
What is cytology?
The study of the structure of cells.
List the main functions of the cell (6 points)
- Basic unit of life.
The cell is the smallest part to which an organism can be reduced that still retains the characteristics of life.
- Protection and support.
Cells produce and secrete various molecules that provide protection and support of the body. For example, bone cells are surrounded by a mineralized material , making bone a hard tissue
that protects the brain and other organs and that supports the weight of the body.
- Movement.
All the movements of the body occur because of molecules located within specific cells such as muscle cells
- Communication.
Cells produce and receive chemical and electrical signals that allow them to communicate with one another. For example, nerve cells communicate with one another and with muscle
cells, causing them to contract
- Cell metabolism and energy release.
The chemical reactions that occur within cells are referred to collectively as cell metabolism. Energy released during metabolism is used for cell activities, such as the synthesis of new molecules,muscle contraction, and heat production, which helps maintain body temperature.
- Inheritance.
Each cell contains a copy of the genetic information of the individual. Specialized cells are responsible for transmitting that genetic information to the next generation
What is a cell?
- Smallest structural and functional unit of an organism capable of carrying out life processes under suitable conditions
- This is the basic unit of structure and function in a living organism
What does the cell theory state?
“A cell is the fundamental and functional unit of life”
i.e. the cell is the basic unit of the structure and function in living organisms.
What factors limit cell size?
- Surface area to volume ratio
Small cells have large surface area: Volume ratio (SA: V ratio) while large cells have a small SA: V ratio.
A large SA: V ratio enables fast rate of diffusion while a small SA: V ratio slows the rate of diffusion.
Small cells have low metabolic demands and form low amount of wastes while large cells have higher metabolic demands and form much amount of wastes.
Therefore, the large SA: V ratio in small cells enables adequate supply of oxygen and nutrients and expulsion of wastes e.g. carbon dioxide via the surface of the cell by simple diffusion while the small SA: V ratio in large cells limits diffusion hence the supply of nutrients by simple diffusion is inadequate to meet the metabolic demands of the cell.
- Nucleocytoplasmic ratio
DNA in the nucleus provides instructions for protein synthesis hence controls activities of the whole cell.
Each nucleus can only control a certain volume of cytoplasm.
Specialization forms some long / large cells, therefore to overcome this limitation such cells are modified to become multinucleate / coenocyte e.g. skeletal muscle cells and fungal hyphae.
- Fragility of cell membrane
As cell size increases, the risk of damage to the cell membrane also increases. This limits the maximum size of cells, especially animal cells.
Hence;
(i) In animals, some large sized cells take in substances in bulk by endocytosis and expel bulk
substances by exocytosis to supplement on simple diffusion.
(ii) Some animal cells increase their surface area by forming many tiny projections called microvilli.
(iii) Some cells divide when they reach a certain size to maintain suitable SA: V ratio.
Note: SA: V ratio particularly limits the size of bacterial cells, i.e. prokaryotic cells which are incapable of endocytosis and exocytosis.
- Mechanical structures that hold the cell together
Cells with tough cell walls e.g. plant cells are larger than cells with only the fragile cell membrane e.g. animal cells because the tough walls provide support and maintain cell shape.
Cells with complex internal cytoskeleton are larger than cells with little cytoskeleton because the cytoskeleton protects and supports the cell structure and maintains cell shape.
State the two types of cells?
The Prokaryote/ Prokaryotic cell
(Pro, before; karyon, nucleus) and the Eukaryote/ Eukaryotic cell (Eu, true; Karyon Nucleus) cell.
State characteristics of Prokaryote cells
- They have no membrane bound organelles.
- Their nuclear material lies in a free region known as a nucleoid e.g. in bacteria.
- The cell has no distinct nucleus. The nucleoplasm appears scattered in the cytoplasm or the nuclear
materials e.g. DNA. - The cell lacks a nuclear membrane/ envelope
- Each cell has got very few cell organelles (cell parts) e.g. they do lack the chloroplasts and mitochondria.
- The cell has circular strands of DNA in the cytoplasm, not contained in a nuclear membrane (no chromosomes)
- They are extremely small, ranging in size between 1-10milimetres in diameter
- Duplication of the chromosomes occurs but not on the spindle i.e. their cells are capable of multiplication
- The cell has got a unique cell wall containing a polysaccharide Examples include bacteria and cyanobacteria
Define ‘Eukaryotic cells’
These are cells with a true nucleus.
Their nuclear materials are found inside the nucleus surrounded by two membranes.
They probably evolved about 1000 million years ago, 2 million years after the prokaryotes.
What are the two main kinds of Eukaryotic cells?
- Plant cells
- Animal cells
Define a ‘light microscope’
A light microscope is a microscope that uses light as a source of radiation.
Under the microscope, cells are described as a small unit of living protoplasm and always surrounded by cell surface membrane and sometimes as in plants, surrounded by a non-living cell wall made of cellulose.
The most conspicuous structure is the nucleus which contains a deeply staining material known as chromatin.
When loose it is referred to as chromosome.
Chromosomes appear as thread like structures just before nuclear division.
The living material between the nucleus and the cell surface is known as the cytoplasm which contains a variety of organelles.
Define a ‘generalized cell’
This is a cell which shows all the typical features found in a cell.
Describe the features of an animal cell under the light microscope
- Contains protoplasm ( nucleus and cytoplasm) surrounded by a thin plasma membrane.
-Relatively large central nucleus surrounded by the cytoplasm.
-The nucleus contains coiled threads called chromatin.
-Chromatin contains DNA and proteins called histones which together condense to form chromosome during cell division.
-(DNA carries genetic material which controls cell activities and determines the organism’s characteristics.)
-The cytoplasm contains organelles suspended within.
Describe the structures of a plant cell under a light microscope
NB: A typical plant cell has additional specialised structures as well as many of those found in an animal cell.
- Protective, rigid, cellulose cell wall surrounding the cell.
-Plant cells have a nucleus and cytoplasm which are usually peripheral.
-The cytoplasm contains chlorophyll pigments which carry out photosynthesis.
-A large central vacuole filled with cell sap is present in mature plant cells.
- The vacuole is surrounded by the tonoplast
The most conspicuous/ clearly visible structure of the cell is the (dash) which contains chromatin.
Nucleus
- Chromatin is the loosely- coiled form of chromosomes.
- Chromosomes contain genetic material in the form of DNA.
- The nucleus is separated from the cytoplasm by its nuclear membrane
- The cytoplasm contains organelles.
State similarities between prokaryotic and eukaryotic cells
-Both have vacuoles
-Genetic material (DNA)
-Ribosomes
-Vesicles
-Cytoplasm
-Cell membrane
State differences between prokaryotic cells (p cells) and eukaryotic cells (*e cells)
P cells; The nuclear material is not enclosed by nuclear envelope
E cells;
The nuclear material is enclosed by nuclear envelope
P cells;
Organelles are not membrane bound
E cells;
Organelles are membrane bound
P cells;
Binary fission/ conjugation occurs
E cells;
Mitosis, meiosis or both can occur
P cells;
Have 70S ribosomes
E cells;
Have both 70S and 80S ribosomes
P cells;
Use mesosomes for respiration
E cells;
Use mitochondria for respiration
P cells;
Flagella if present, lack microtubules
E cells;
Flagella, if present, have a ‘9+2’ arrangement of microtubules
P cells;
Have circular DNA
E cells;
Have linear DNA
P cells;
Have photosynthetic lamellae
E cells;
Have chloroplasts in (plants and algae)
P cells;
Rigid cell wall containing murein (peptidoglycan)
E cells;
Cell walls of plants and algae contain cellulose, fungi contain chitin and animal cells have no cell walls
P cells;
Smaller in size
E cells;
Larger in size
What is the only organelle found in animal cells which is absent from plant cells?
The centriole
State advantages of having membrane bound organelles
- Potentially harmful reactants (enzymes) can be isolated inside an organelle so that they do not harm the rest of the cell
- The rate of any metabolic reactions inside an organelle can be controlled by regulating the rate at which the membrane allows the first reaction to occur or to enter
- The containment of enzymes for a particular metabolic pathway within the organelle means that the products of the reaction will always be in close proximity to the next enzymes within the sequence.
This increases the rate of metabolic reactions
- Many metabolic processes which involve enzymes occur in the membrane.
What is the function of flagella in prokaryotic cells?
Propulsion
What is an organelle?
An organelle can be defined as a membrane-enclosed
structure with specialised functions, suspended in the cytosol of eukaryotic cells.
State an example of prokaryotic cells
- Bacteria
State the main components of the cell membrane
- Phospolipids
- Proteins
- Cholesterol
- Carbohydrates
Where are mitochondria abundant?
- Kidney nephron
- Muscle fibres
- Neuron axons
- Tail of sperms
- Root hairs
What are prokaryotic cells?
These are cells whose DNA is not enclosed in a nuclear envelope; they lack a true nucleus and their organelles are not membrane bound
Their DNA lies free in the cytoplasm in an area called the nucleoid
True or false;
The flagella of prokaryotic cells lack microtubules
True
Which organelle of the prokaryotic cell is useful in respiration?
Mesosome
What are the plasmodesmata?
These are fine threads that link the cytoplasm of neighboring cells through the cell walls
True or false;
Only plant cells are able to carry out photosynthesis
False
Prokaryotic cells may have photosynthetic lamellae which contain photosynthetic pigments, allowing them to photosynthesize
What is the difference between plasmids and plastids?
Plasmids are circles of DNA able to replicate independently of the main circular chromosome which aid survival of bacteria in adverse conditions
While
Plastids are organelles containing pigments
Explain the symbiotic theory
The symbiotic theory states that some of the organelles in eukaryotic cells were once prokaryotic microbes.
- It suggests that mitochondria and chloroplasts were once separately existing small anaerobic bacteria and photosynthetic bacteria respectively.
- Larger anaerobic bacteria engulfed the smaller bacteria by the process of endocytosis but digestion failed.
- Initially, smaller bacteria might have lived as parasites or phagocytic vesicles after which endosymbiosis resulted (smaller organisms removed oxygen and the larger organisms provided protection)
- With time, mitochondria and chloroplasts were modified into organelles for respiration and photosynthesis inside larger eukaryotic cells
Summary:
- Larger prokaryotes engulfed smaller ones
- Smaller ones were not digested
- They began to depend on each other
- Mitochondria and chloroplasts carried out respiration and photosynthesis thus removing oxygen from eukaryotic cells
Give features of Eukaryotic cells
- Nuclear envelope
- Linear DNA
- Membrane bound organelles
- Many ribosomes
Give differences between plant and animal cells
Plant cells;
- Cellulose cell wall in addition to the cell membrane
- Large central vacuole
- Starch grains used for storage
- Centrioles absent
- Nucleus is peripheral
- Cytoplasm is peripheral
- Tonoplast around vacuole
Animal cells;
- Only have cell membrane
- Vacuoles if present are small and scattered throughout the cell
- Glycogen granules used for storage
- Centrioles present
- Nucleus is often central
- Cytoplasm present throughout the cell
- Tonoplast absent
Give proof/ evidence of the symbiotic theory
- Mitochondria and chloroplasts have their own circular DNA different to that of eukaryotic cells
- Mitochondria and chloroplasts can self-replicate
- Presence of 70S ribosomes in both mitochondria and chloroplasts as well as prokaryotes
- DNA replication in prokaryotes, mitochondria and chloroplasts takes place by binary fission while in eukaryotes it is by mitosis/ meiosis
- Presence of double membrane bound organelles
Describe the structure of the nucleus
- Has a double membrane called the nuclear envelope
- The outer membrane is continuous with rough ER
- Has a cytoplasm-like material called the nucleoplasm
- Contains chromatin/DNA/ genetic material
- Has a spherical nucleolus
- Nuclear membrane is perforated / has pores
Give the functions of the nucleus
- Contains the hereditary genetic material of the cell
- It is the center to control cell activities
- Produces ribosomes and RNAs needed for protein synthesis
- Carries instructions for formation of proteins
- Nuclear division gives rise to cell division, hence reproduction
Give adaptations of the nucleus to its function
- The nuclear membrane is perforated for exchange of DNA and RNA between the nucleus and the cytoplasm
- DNA contained in the nucleus is long to store genetic information
- Presence of the nucleolus which produces ribosomes for protein synthesis
- The nuclear envelope provides a compartment for reactions to take place in the nucleus
- Nuclear pores are narrow to regulate entry and exit of substances
Describe the structure of chloroplasts
- They are oval shaped
- Double membrane bound (chloroplast envelope)
- Have a colorless matrix called the stroma
- Have grana
- The grana are made up of flattened sacs called thylakoids
- The thylakoids have photosynthetic pigments eg chlorophyll
- Some thylakoids have tubular connections which connect adjacent grana
- Starch grains are also present
- Small amount of circular DNA present
- Oil droplets present
Give functions of the chloroplast
- Manufacture of food via photosynthesis
- Produce fatty acids
- Store starch
- Produce new pigments eg chromoplasts
- Produce oxygen
Describe the structure of the mitochondrion
- Double membrane bound
- Inner membrane is folded inwards into cristae
- Has stalked particles
- Has a matrix made if semi-rigid material
- Has 70S ribosomes
- Fluid filled intermembrane space
Give the functions of the mitochondrion
Site of aerobic respiration
Describe the structure of the rough endoplasmic reticulum
- Double membrane bound
- The membrane is continuous with the nuclear envelope
- Encrusted with ribosomes
- Has sac-like structures called cisternae
- Perforated membrane
Give the functions of the rough ER
- Isolate and transport proteins
- Maintain cell shape
Give the function of the smooth ER
- Synthesis and transport of lipids and steroids
- Stores calcium ions used in muscle contraction
- SER of the liver contains enzymes to carry out detoxification
Give differences between the rough ER and the smooth ER
ROUGH
- Has ribosomes on its membrane
- Transports mainly proteins
- ER membrane is continuous with nuclear membrane
- Flattened sacs
SMOOTH
- Does not have ribosomes on its membrane
- Transports lipids
- ER membrane is not continuous with nuclear membrane
- Tubular cavities
Describe the structure of the golgi body (dictyosome in plants)
Numerous vesicles
Give the functions of the golgi body
- Synthesis of lysosomes
- Replenishes the cell membrane
- Synthesis of peroxisomes
- Modifies and transports proteins
Describe the structure of the lysosome
- Spherical shape
- Single membrane bound
- Contain hydrolytic enzymes
Give the functions of the lysosome
- Play a role in immunity
- Digestion of materials taken in by endocytosis
- Destroy worn out organelles
Define autophagy
Process by which unwanted cell structures are engulfed and destroyed within lysosomes
Define autolysis
Process by which lysosomes release their content into the cell thus breaking down the entire cell
Distinguish between the structure of a chloroplast and that of a mitochondrion
CHLOROPLAST
- Contains photosynthetic pigments that absorb light
- Cristae absent
- Larger size
- Biconvex shaped
- Thylakoids present
- Matrix is the stroma
- Have grana
- Have starch granules
MITOCHONDRION
- Non-pigmented
- Highly folded to form cristae
- Smaller size
- Sausage shaped
- Thylakoids absent
- Mitochondrial matrix
- Do not have grana
- Phosphorus granules for ATP production
substances, from the cell
- Maintain cell shape
- Enable separate compartments within a cell to be formed
- Isolate, harmful reagents, such as enzymes
- Control the rate of chemical reactions to changing permeability
- Cell secretions are added by cell membranes
- The inter-membrane space of the mitochondrion is a crucial site for ATP synthesis
Describe the structure of microbodies/ peroxisomes
- Single membrane bound
- Contain numerous catalase enzymes
Give the functions of the peroxisome
- To get rid of toxic hydrogen peroxide
Describe the structure of vacuoles
- Fluid filled sac
- Single membrane bound
- In plants the membrane is called the tonoplast
Give the functions of plant vacuoles
- Temporary food store
- Give petals bright colors for attracting insect pollinators
- Temporary stores for organic waste
- Contain hydrolytic enzymes that break down waste
- Support herbaceous plants
- Bring about cell elongation
Describe the structure of ribosomes
- Made up of one large and one small subunit
- Small
- Non-membranous
- Some are bound to the rough endoplasmic reticulum, and others are free
Give the function of the ribosome
- Sites of protein synthesis
Describe the structure of microtubules
- slender unbranched tubes
- Non-membranous
Give the functions of micro tubules
- form spindle fibers involved in cell division
- Maintain cell shape
- Form a framework along which the cellulose cell wall of plants is laid down
- Major component of cilia and flagella, which contribute to movement of the cell
Describe the structure of cilia and flagella
CILIA
- Often numerous
- Typically shorter
FLAGELLA
- often few
- Typically longer
- Both are enclosed by a plasma membrane
- Consist of internal microtubules
Give the functions of cilia and flagella
- propulsion
- To sense the environment
- Movement of material
- Aids locomotion and movement
True or false centrioles are absent in plant cells
True
Describe the structure of centrioles
- hollow cylinders
- Small
- Contain nine triplets of microtubules
Give the function of centrioles
Form spindle fibers
Describe the structure of the cell wall
- Made up of cellulose
- Has three main layers
- Interconnected (have plasmodesmata)
Give the functions of the cell wall
- Provide support in herbaceous plants
- Maintain cell shape
Describe the Danielli- Davidson hypothesis of the plasma membrane
- The membrane has two molecules, lipids, and proteins
- The lipids are sandwiched between two protein layers
- Inwardly directed hydrophobic tails
- One head with two tails
- The membrane is rigid
Describe the fluid mosaic model
- The plasma membrane is made up of phospholipids
- The phospholipids have a head and a tail
- They have hydrophilic phosphate, heads and hydrophobic tails of fatty acids
- The tails face inwards and the heads face outwards
- It has cholesterol between the phospholipid molecules which maintains the fluidity of the membrane
- It has proteins that occur, extrinsically, intrinsically, and transmembrane
- The proteins from a mosaic, hence the name fluid mosaic model
- Some proteins and lipids have carbohydrates attached to them, for example glycoproteins and glycolipids, respectively
- The membrane is approximately 7 to 8nm
Give proof of the fluid mosaic model
Freeze fracturing.
A piece of cell membrane is frozen, split down the middle longitudinally and viewed in an electron microscope.
Globular structures of the same size as the membrane proteins are seen scattered about confirming the fluid mosaic model.
Give the similarities between the sandwiched theory, and the fluid mosaic model
- both consist of proteins and lipids
- Lipids, in both cases a hydrophobic
- BothBoth suggest that phosphates are hydrophilic
State differences between the sandwiched theory and fluid mosaic model
SANDWICHED THEORY
- suggest that the cell membrane is rigid
- Cholesterol is absent
- Suggested proteins are only extrinsic
- Carbohydrates absent
FLUID MOSAIC MODEL
- suggest that the cell membrane is fluid
- Cholesterol is present
- Suggested proteins are extrinsic, intrinsic or span across the membrane
- Has carbohydrates
Give the functions of proteins in the cell membrane
- they act as enzymes catalyze reactions
- They aid facilitated diffusion
- Useful in cell to cell recognition
- They are receptor molecules
- They join cell to cell forming a tissue
- They give structural support to the cell
Give the function of glycolipids and glycoproteins in the cell membrane
- Play a role in cell to cell recognition
- They are receptor sites
Give the function of cholesterol in the cell membrane
- maintain fluidity and flexibility of the membrane
(When temperatures are low, they make the cell membrane more fluid to prevent solidifying, and when temperatures are high, they make the cell membrane less fluid)
Give the function of phospholipids in the cell membrane
- Prevent the entry or exit of polar molecules
- Maintain flexibility and fluidity of the cell membrane
Give the general functions of membranes
- Control the rate of chemical reactions by changing permeability
- Protective barriers to pathogens
- Prevent the escape of useful substances, from the cell
- Maintain cell shape
- Isolate, harmful reagents, such as enzymes
- Cell secretions are added by cell membranes
- The inter-membrane space of the mitochondrion is a crucial site for ATP synthesis
- Membranes are vital in excretion as excretory products are packed in vesicles, which are membrane-bound
- Increase the efficiency of the cell through compartmentalization
- Nuclear membrane contains genetic material which prevents it from being altered in the cytoplasm
- Secretions are packaged in membrane bound vesicles and transported to their site of secretion
- Useful in immunity as pathogens are broken down in membrane bound lysosomes
Give the advantages of organisms being multicellular
- Increased possibility of specialization
- Storage of more materials, and better ability to overcome periods of scarcity
- Competitive advantage
- Better developed muscles and skeletons for defense
What are the disadvantages of organisms being multicellular?
- High metabolic demand
- The cells lose independence
- Exposure to predation
Where may DNA be found in a cell?
- Nucleus
- Mitochondria
-Chloroplast
Where may RNA be found in the cell?
- Nucleus
- Cytoplasm
