Topic 2: Cells Flashcards
What is the mitochondria?
The powerhouse of the cell 💪😡🧬
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What are cells?
Cells are the structural unit of all living things, the basic functional unit of life, not only making up the bodies of living things but they also carry out the ‘life processes’.
What is the cell theory?
The cell theory is a concept that unifies all living things.
what does the cell theory state?
The cell theory states that:
All organisms consist of one or more cells
The cell is the basic structural and functional unit of all living things
All cells arise from pre-existing cells
(Most) cells contain hereditary information (DNA) which is passed on to daughter cells.
Cells use energy
What are some features that distinguish living things from non-living things?
Living things:
Are complex and have an organised structure
Take in energy from their surroundings and use it
Preserve a composition that is chemically different from that of their external environment
Respond to stimuli
Are able to reproduce themselves
Grow and develop
What encloses the cytoplasm (internal fluid) of the cell?
All cells are made up of an outer membrane called the cell membrane which encloses the cytoplasm.
What is cytoplasm and what does it contain?C
Cytoplasm is a fluid inside cells made up of mainly water and contains many smaller structures called organelles (small organs).
What can a cell be defined as?
A cell can be defined as a unit of living matter (protoplasm) that is separated from its external surroundings by a membrane which regulates the passage of materials into and out of the cell.
What are the main functions of the cell membrane?
Separate the contents of the cell from the external environment
Regulate the passage of substances into and out of the cell
Enable cells to recognise each one other, and to recognise certain hormones
Enable attachment of the cytoskeleton
Describe current model of the cell membrane.
The cell membrane is made up of two layers of phospholipid, a phospholipid bilayer.
It is a dynamic living structure, where proteins and lipids penetrating it at various points can move around, known as the fluid mosaic model.
This is able to explain how substances move through the permeable membrane, and hence, into and out of cells.
What are lipids/phospholipids?
Lipids are molecules that contain only carbon, hydrogen, and oxygen making up fatty acids that join together to form a lipid molecule.
Phospholipids are lipids with a phosphate group. They make up the bilayer of the cell membrane.
The heads (phosphates) are hydrophilic and align to be facing outside, in contact with water.
The tails (lipids) are hydrophobic and form the interior of the membrane, reducing exposure to the water
What does cholesterol do to a cell membrane?
Cholesterol provides structural support so that the bilayer is more stable and fluidity is reduced - “regulates fluidity of the cell membrane”.
There are various types of proteins that are a part of the cell membrane, what are they?
Integral proteins - span across both layers of the membrane and are permanently there, used in transport across the membrane.
Peripheral proteins - in one of the two layers and can move and are temporary, used in enzymic reactions.
Glycoproteins - proteins attached to carbohydrates on the surface, allow other molecules (e.g., hormones) to bind.
What are glycolipids and what are they for?
Glycolipids are lipids with a carbohydrate attached, they recognise other cells of the body.
Compare the roles of lipids and proteins in the cell membrane.
While lipids help to give membranes their flexibility, proteins monitor and maintain the cell’s chemical climate and assist in the transfer of molecules across the membrane.
What are some of the functions of proteins in the cell membrane?
Transport materials in and out i.e., channel proteins.
Enzymes speed up reactions along a membrane.
Receptors receive information.
Cell adhesion - can allow cells to stick together.
Cell-cell recognition - allows cells to communicate with each other by proteins attaching.
Describe the structure of prokaryotic cells.
Very small, <10um
Have simple internal organisation
Have circular and unbound DNA found free-floating in the cytosol in the nucleoid region
Do not have membrane-bound organelles (only have ribosomes which are smaller than those in eukaryotic cells)
Often have flagella (like a tail) for movement and pili to stick to other cells
All prokaryotes are unicellular organisms.
Describe the structure of eukaryotic cells.
The DNA is condensed around proteins that form linear chromosomes located in the nucleus
Have more complex internal organisation and are generally bigger, 10-100um
Contain membrane-bound organelles, ‘compartmentalised’
What do bacteria, archaea, and plant cells have in common?
Bacteria, archaea, and plant cells all have outer cell walls along their cell membranes, each have cell walls made of different substances.
Describe eukaryotic organisms.
Eukaryotic organisms differ greatly from one another in size, shape, colour and complexity
Whilst there is a great diversity among eukaryotic organisms, they are made up of cells that have similar features, including membrane-bound organelles
Eukaryotic organisms can be both unicellular and multicellular
Prokaryotic and eukaryotic cells have many features in common, what are some and what does this reflect?
They both have a phospholipid cell membrane
A fluid-like matrix filling the cell (cytoplasm and cytosol)
A cytoskeleton structure within the cell
Similar protein synthesis mechanisms (using ribosomes)
The same genetic code system (DNA and RNA)
This is a reflection of their common evolutionary past, showing they have similar ancestors to have similar features.
Compare the structure of animal and plant cells.
Animal cells are typically round or irregular in shape, where plant cells are typically rectangular or cubic
Animal cells are typically 10-30um, plant cells are typically 10-100um
Plant cells contain larger vacuoles than animal cells
Both have cell membranes, but plant cells also have a cell wall made of peptidoglycan
Due to this, plant cells do not have cholesterol in the cell membrane, where animal cells do
Plant cells have chloroplasts
Describe the structure of fungal cells
Fungi are saprophyte heterotrophs, they secrete enzymes to breakdown and digest dead or decomposing matter
They do not need chloroplasts to produce energy
Grow as a tangle of long, threadlike hyphae, a branching structure
As more hyphae grow they divide into separate cells by forming septa
Cell wall made from glucans and chitin instead of peptidoglycan (plant cells)
Ergosterol instead of cholesterol (animal cells) in the cell membrane for stabilisation of the membrane
Provide some examples of fungal organisms.
Yeasts - unicellular fungi
Moulds and mushrooms - multicellular fungi
Describe the structure of the nucleus and its function.
The nucleus controls the activities of the cell.
Composed of a double membrane boundary called the nuclear envelope, containing many nuclear pores lined with proteins
It is able to determine which enzymes are made and thus determines which chemical reactions take place, and even what structure the cell will have
When a cell is not dividing, the nucleus has a grainy appearance and its contents are referred to as chromatin (which has no distinctive shape)
Describe the structure of the nucleolus and its function.
Inside the nucleus ,there may be one or more circular regions that are very distinguishable from the rest
These are nucleoli, and are not bounded by a membrane
They are composed of DNA and protein and are the site of ribosomal RNA synthesis
Describe the structure of the mitochondria and its function.
Sausage-shaped organelle roughly 10um containing an outer and inner membrane
The inner membrane is folded to form structures called cristae
The latter stages of aerobic respiration are carried out inside the mitochondria and a great deal of energy is released from this reaction
This explains why it is often referred to as the powerhouse of the cell, and explains why some cells, such as muscle cells, which require a lot of energy, have abundant mitochondria
Contain their own circular mitochondrial DNA and ribosomes, both of which work to produce proteins for the mitochondria
Describe the structure of the chloroplast and its function
They are a type of plastid.
Inside the double membrane there are membranous flattened sacs called thylakoids, some of which are arranged into stacks called grana (singular granum)
The fluid which surrounds the thylakoids is called stroma
The thylakoid membranes contain photosynthetic pigments such as chlorophyll, and their function is to carry out photosynthesis
The first stage requires light energy and occurs in the grana
Enzymes that catalyse the many steps of the process are located in the grana and stroma
Chloroplasts contain their own circular DNA and ribosomes
What is so special about mitochondria and chloroplasts?
Both mitochondria and chloroplasts contain their own circular DNA and ribosomes, both of which work to produce necessary proteins
Evidence that they were possibly their own bacteria that functioned on their own and were incorporated into cells at some stage
Describe the structure and function of the vacuole
A vacuole is a fluid filled space bounded by a membrane
In it there is a watery solution, with solutes such as salts, simple sugars, and amino acids
It maintains the water and salt balance of the cell
Most mature plant cells have a large, central vacuole that provides structural support
Animal cells tend to have many smaller vacuoles
They may also be used to store the cell’s waste products, and some contain pigments
Compare vacuoles in plant cells and other eukaryotic cells
Unlike plant cells, other eukaryotic cells do not contain large central vacuoles
Vacuoles found in animal cells are usually much smaller and more numerous
Other cells can have vacuoles such as food vacuoles and contractile vacuoles
Food vacuoles are formed when a cell engulfs a particle by phagocytosis
Describe the structure of a vesicle and its function.
A small vacuole is called a vesicle
May be involved in phagocytosis, and with Golgi bodies in exocytosis
There are also specialised vesicles, such as lysosomes
Describe the structure of the Golgi body and its function.
The Golgi body is a stack of flattened sacs made of smooth membrane
They are involved in the packaging and secretion of proteins and carbohydrates manufactured by the cell
They are abundant in cells involved in secretion such as gland cells like salivary glands, which secrete saliva
It also manufactures some carbohydrates for use outside the cell
These are packaged into vesicles that bud off from the Golgi body and migrate to the cell membrane where they fuse with it and release their contents
This secretion is an example of exocytosis (exo=out of, cytosis=the cell)
What is the endoplasmic reticulum?
The endoplasmic reticulum (ER) is a system of membranes that extends throughout the cytoplasm from the nuclear envelope to the cell membrane
It forms an intricate network of passageways throughout the cell and is important in the transport of materials from one part of the cell to another
What is the rough endoplasmic reticulum?
Some endoplasmic reticulum has ribosomes attached to it and this is referred to as rough endoplasmic reticulum, due to its appearance
Rough ER is mainly the site of protein synthesis (and for transport)
What is the smooth endoplasmic reticulum?
Endoplasmic reticulum without ribosomes attached to it is called smooth endoplasmic reticulum, and it tends to be involved in metabolic processes such as lipid synthesis and carbohydrate metabolism
It can be thought of as a ‘workbench’ for many metabolic processes, since certain enzymes are embedded in it
Describe the structure of the ribosome and its function
A ribosome is made of RNA and protein
The RNA in ribosomes is a special type, produced in the nucleolus, ribosomal RNA (rRNA)
It is not enclosed by a membrane
It is the site of protein synthesis
Describe the structure of the lysosome and its function
A vesicle containing digestive enzymes
In some cells, lysosomes fuse with food vacuoles and release digestive enzymes, which break down the food
Certain cells of our immune system that are involved in engulfing and destroying foreign particles like bacteria also use lysosomes
Lysosomes are also involved in programmed cell death (apoptosis)
What is the cytoskeleton? What is it made up of?
The cytoskeleton is a structure that helps cells maintain their shape and internal organisation, whilst also helping them carry out certain functions
All eukaryotic cells have a cytoskeleton which is made up of three main components:
Microfilaments
Intermediate filaments
Microtubules
The filaments and microtubules of the cytoskeleton are made up of subunits which can be rapidly removed or inserted into the existing structure to change its shape - much like the temporary scaffolding at a building site
The cytoskeleton is therefore a dynamic structure
What are the main functions of the cytoskeleton?
To give cells their shape
To be involved in cell movement
To hold organelles in place
To strengthen cells
Describe the structure and function of microfilaments (cytoskeleton).
Microfilaments, made of the globular protein actin, are involved in intracellular movement like cytoplasmic streaming, chloroplast orientation, the pinching in of the cell membrane to form daughter cells after cell division, and the formation of a food vacuole by the process of phagocytosis
The contraction of muscle is due to one group of microfilaments interacting with one another
Actin proteins are also found in some prokaryotes
Describe the structure and function of microtubules (cytoskeleton).
Microtubules, made of the protein tubulin, are an essential part of the flagella and cilia, fine hair-like projections found on many cell membranes
The coordinated beating of these structures causes fluid movement, so that either the cell moves of fluid moves past the cell
Unicellular organisms often use cilia to move around its environment, while epithelial cells in the airways of our lungs use cilia to move mucus out of the lungs
Describe the structure and function of intermediate filaments (cytoskeleton).
Intermediate filaments are made up of strong fibrous proteins and they are found in cells, such as skin cells, that are subject to wear and tear
The function of the intermediate filaments is to strengthen these cells and their tissues
How does the cytoskeleton affect cell structure?
A human red blood cell is formed into a bi-concave shape, rather than a sphere, by its cytoskeleton, and this gives it a high surface area to volume ratio suitable for transporting oxygen
A nerve cell, with its very long axon, is another example of a cell shape that would be impossible without a cytoskeleton
It enables some cells to have highly specialised structures
How are organelles in a cell held in place?
The organelles in the cell are held in place by the cytoskeleton
For example, the chloroplasts in plant cells are held near the surface of the cell with the correct orientation to receive maximum light
How is movement in a cell possible?
Movement within a cell is made possible by the cytoskeleton
For example, the spindle apparatus formed to move chromosomes in cell division is a specialised microtubule structure
How is the abstract concept of energy defined?
Energy is defined as ‘the capacity to do work’
The more energy an animal or plant has, the more work it can do
What needs energy and why?
All living things need energy to carry out essential life processes such as movement involving the whole cell or movement within the cell, and synthesis of compounds such as proteins, carbohydrates, lipids and nucleic acids
By performing these tasks cells are able to grow, repair, reproduce, and function normally
Where can cells obtain energy from to carry out their life processes?
Cells can obtain energy to carry out their life processes in either physical or chemical form
Some cells can use sunlight, a physical form of energy, while others must take in energy-rich compounds, a chemical form of energy
In both cases the energy that enters the cell is then transformed so that it is useful to the cell
All cells produce heat as part of their chemical activities
What are autotrophs?
Autotrophs are organisms (autotrophic cells) that are able to make all the energy-rich compounds they need from inorganic substances
Most use sunlight, a physical form of energy, for the synthesis reaction of photosynthesis, as the Sun is the main source of energy for life on earth
Organisms that photosynthesise are called photosynthetic autotrophs
Chemosynthetic reactions are carried out by some rare single-celled organisms to make food molecules from simple raw materials
What are heterotrophs? Example?
Heterotrophs are organisms (heterotrophic cells) that cannot produce all of their organic compounds from simple inorganic substances, and so they rely on other organisms, or their products or remains, for ‘food’
An example is the snail obtaining its organic compounds from grass, and the lizard obtains some of its organic compounds from snails. The kookaburra, in turn, obtains some of its organic compounds from the lizard. Ultimately, the kookaburra’s organic compounds have come from the grass (an autotroph)
Simply compare autotrophs and heterotrophs
Autotrophs make their own organic compounds, whereas heterotrophs must obtain at least some of their organic compounds by feeding
What is the formula for photosynthesis?
6CO2 + 6H2O sunight,chlorophyll-> C6H12O6 + 6O2
Carbon dioxide + water sunlight,chlorophyll-> glucose + oxygen
What is a transformation of energy?
A transformation of energy is the conversion of a form of energy to another through the formation and breaking of chemical bonds
What is photosynthesis and where does it occur?
In photosynthetic eukaryotic cells (plant cells) photosynthesis occurs in chloroplasts, where light energy is used to convert carbon dioxide and water into glucose, a simple sugar
Chlorophyll, the green pigment that absorbs light, is located in the thylakoid membranes of the grana
Enzymes that catalyse the many steps of photosynthesis are found in the grana and stroma
In photosynthetic prokaryotic cells (cyanobacteria) photosynthesis occurs in the cytoplasm which contains the chlorophyll and necessary enzymes
When is there a net output of energy in a chemical reaction?
There is a net output of energy in a chemical reaction when the energy in the reactants is greater than the energy in the products
How does glucose release energy?
The breakdown of glucose in the presence of oxygen releases energy, as the energy in the reactants is greater than the energy in the products.
This is because the amount of energy required to break the bonds in the glucose and oxygen molecules (reactants) is less than the amount of energy released when the bonds in carbon dioxide and water (products) are formed
Some of this energy released can be used by the cell to do work, while the rest is lost as heat
What is ATP? Describe its structure and its formation
ATP, adenosine triphosphate, is one of the most important energy storage compounds in cells, and is a short-term energy storage compound
ATP consists of the nitrogen base adenine bonded to the sugar ribose, which in turn is bonded to three phosphate groups, called a triphosphate
The third phosphate group is held to the others by an unstable bond
The energy needed to produce ATP from ADP and Pi comes from cellular respiration
ADP + Pi -> ATP + water
Describe the conversion of ATP to ADP and Pi
When ATP is broken down to form ADP (adenosine diphosphate) and Pi (an inorganic phosphate group), energy is released
This energy can be used by the cell to drive many processes that require energy, such as synthesis, cell movement, endocytosis and exocytosis
ATP -> ADP + Pi + energy
Why do cells/organisms need to respire?
All living cells, and hence organisms, need to respire in order to obtain the energy to carry out essential life processes
Cellular respiration provides this energy by breaking down energy-rich organic molecules into lower energy products
What are the two types of respiration? Compare them.
The two types of respiration are aerobic respiration and fermentation (anaerobic respiration)
Both reactions use glucose as their starting point, but produce different products
The most efficient of the two is aerobic respiration, which, like many other chemical processes in the cell, consists of a series of small steps - a metabolic pathway
Each step in the pathway is catalysed by a specific enzyme
What is the formula for aerobic respiration?
C6H12O6 + 602 -> 6CO2 + 6H20
Glucose + oxygen -> carbon dioxide + water
The reactants and products for photosynthesis and aerobic respiration are the same but reversed, but both undergo different processes to achieve them
Describe the process of aerobic respiiration
Aerobic respiration begins with the conversion of glucose to an intermediate compound called pyruvic acid
This metabolic pathway is called glycolysis and it occurs in the cytoplasm
One glucose molecule breaks down to produce two pyruvic acid molecules. The energy of this breakdown produces a net gain of two ATPs
The next two stages occur inside the mitochondria
First, the two molecules of pyruvic acid produced by glycolysis are converted to acetyl coenzyme A (acetyl CoA) which enters the Krebs cycle
The acetyl CoA molecules are then broken down to carbon dioxide and water
The final stage is called phosphorylation, and its function is to add a phosphate group to ADP using the energy released from the pyruvic acid breakdown, thus making the energy-rich molecule ATP
The energy for phosphorylation is obtained from glycolysis and the Krebs cycle in which electrons are transferred from one molecule to another
Compare glycolysis in other living things.
All organisms carry out glycolysis in exactly the same way using the same enzymes to catalyse the same steps, evidence that all living things evolved from a common ancestor
Summarise aerobic respiration
In summary, glycolysis and the Krebs cycle break down glycose and are energy releasing processes, whilst phosphorylation synthesises ATP and is an energy transferring process
As a result of the completion of the two stages in the mitochondria, enough energy is released to make about 34 more ATPs, thus about 36 ATPs are produced from the aerobic respiration of one glucose molecule
What does the mitochondria do in aerobic respiration?
The role of mitochondria is vital in the later stages of aerobic respiration, providing four separate regions for the different reactions to occur:
The outer membrane
The space between the outer and inner membrane
The inner membrane
The space inside the inner membrane
Each of the proteins and enzymes that are necessary is located in one particular region
What is fermentation?
Many cells are also able to respire in the absence of oxygen, a process called fermentation or anaerobic respiration
It also uses a fuel such as glucose, but the harvest of ATP is much less than for aerobic respiration, as the fuel is not completely broken down
The products of fermentation depend on the type of cell involved
In plant cells and yeasts, ethanol and carbon dioxide are the products and the process is called alcoholic fermentation
In animals the sole product is lactic acid and the process is called lactic acid fermentation
What is the formula of fermentation in plants and yeast?
Ethanol fermentation
C6H12O6 -> 2C2H5OH + 2CO2
Glucose -> ethanol + carbon dioxide
What is the formula of fermentation in animals?
Lactic acid fermentation
C6H12O6 -> 2C3H6O3
Glucose -> lactic acid
Why is fermentation so significant?
It is of significant commercial importance
Under anaerobic conditions sugars are converted by yeast into ethanol and carbon dioxide
Yeast is also used in baking - the carbon dioxide gas produced causes the product to ‘rise’, while the oven kills the yeast cells and evaporates the ethanol
