A2.2 Cell Structures

Complete

What are the 3 parts of the cell theory?

1. All living things are composed of cells

2. Cells are the basic units of life

3. New cells are produced from existing cells

What do all cells have?

• All surrounded by membrane

• Contain genetic material

• Have chemical reactions that are catalysed by enzymes

• Cytoplasm

What is deductive reasoning?

Deductive reasoning is an approach where one progresses from general ideas to specific conclusions

What is inductive reasoning ?

start with specific observations and form general conclusions.

What 4 observations led to development of cell theory ? ( Inductive reasoning )

• Cork consists of cells

• Embryos consist of cells

• Elder pith consists of cells

• Toad cartilage consists of cells

What is cytology?

Branch of biology that focuses on cell theory

How is cytology an example of deductive reasoning ?

It has led our understanding of cells to theorise that all living organisms are made of at least one cell and therefore any newly discovered living organisms on Earth, will also be made up of at least one cell

What does the presence of DNA mean ?

a new cell can be formed from an old cell, as genetic material is able to be stored and transferred

What additional systems do DNA control ?

the production of enzymes and other vital proteins within the cell

What is cytoplasm composed of ?

mainly water with dissolved substances, such as ions

What is the cytoplasm fluid known as ?

cytosol

What happens in the cytoplasm ?

Many of the cell's important reactions take place within the cytoplasm

What does the plasma membrane do?

• Controls what enters and leaves the cell

• Encloses all cell content

What function do the proteins in the plasma membrane have ?

• Cell recognition

• Cell communication

• Transport into and out of the cell

What are the 2 domains of prokaryotic cells ?

A2.2.5

Bacteria and Archaea ( found in extreme environments )

How big are prokaryotic cells ?

0.1µm to 5.0µm

What structures do prokaryotic cells have?

• 70S ribosomes

• DNA in a loop

• Cytoplasm

• Plasma membrane

• Cell wall

What do 70s ribosomes do ?

they bind and read mRNA during translation to produce proteins

Define the term "naked" in relation to prokaryotic DNA.

DNA that is not associated with proteins for additional packaging

What are plasmids ?

Plasmids are small loops of DNA that are separate from the main circular DNA molecule

What do plasmids contain ?

Plasmids contain genes that can be passed between prokaryotes (e.g. genes for antibiotic resistance)

What form does DNA take in prokaryotic cells ?

Takes the form of single circular DNA molecule

Where are 70S ribosomes found?

Cytoplasm

What is the cell membrane composed of ?

A phospholipid bilayer

What does the cell wall contain ?

murein/peptidoglycan (a glycoprotein)

What does the cell wall do?

acts as protection, maintains the shape of the cell and prevents the cell from bursting

What's gram positive and gram negative bacteria ?

A2.2.5

Gram positive has the ability to retain a dye ( Crystal violet ) and therefore appear blue/violet after exposure E.g Bacillus and Staphylococcus

Gram negative bacteria won't react with this dye

What are capsules ?

A final outer layer surrounding the cell. It helps to protect bacteria from drying out and from attack by cells of immune system

What is the Flagellum ?

Long, tail-like structures that rotate and enable to prokaryote to move

What are the Pili ?

short, hairlike protein structures on the surface of some bacteria. They assist with movement, avoidance of attack by white blood cells and conjugation. They also allow bacteria to adhere to cell surfaces.

Define the term "naked" in relation to prokaryotic DNA.

Refers to DNA that is not associated with proteins, lipids or any other molecule to help protect it

It's not enclosed in a membrane

What's the difference between prokaryotic and eukaryotic cell structure ?

A Prokaryotic cells cytoplasm is one undivided space whereas a eukaryotic cells cytoplasm has many compartments divided by single or double membrane

What does the nucleus do ?

Holds the cells chromosomes.

• Has a double membrane

What is in the nucleus ?

DNA attached to proteins. DNA molecules are linear.

Proteins are histones arranged in globular groups

Whats the difference between ribosomes in prokaryotic and eukaryotic cells ?

Eukaryotic cells have 80's ribosomes whereas prokaryotic has 70's ribosomes.

In eukaryotes they are larger in size

What is the mitochondria?

provides the cell with energy as they carry out aerobic respiration.

• surrounded by a double membrane

What are chloroplasts ?

an organelle surrounded by a double membrane.

produces glucose and other compounds as a result of photosynthesis

What does the rough endoplasmic reticulum do ?

The rER synthesises protein for secretion from the cell. Once synthesised by the ribosomes it passes into the cisterna where it is carried by vesicles which bud off and move to the golgi apparatus.

What is the smooth endoplasmic reticulum ?

The smooth endoplasmic reticulum consists of branches of tubular networks. The membrane is smooth because there are no ribosomes attached.

What does the smooth endoplasmic reticulum do ?

It synthesizes lipids, phospholipids and steroids

• storage of calcium ions in muscles when relaxed

What is the golgi apparatus?

consists of flattened membranous sacs called cisternae. However they are short, do not have ribosomes attached and have many vesicles nearby.

What does the golgi apparatus do ?

Processes proteins brought in vesicles from the rER.

Proteins are then carried to plasma membrane for secretion in vesicles.

What is a vesicle ?

A vesicle is a small vacuole that is used to transport materials inside a cell.

It is a single membrane bound organelle that has fluid inside.

What's a vacuole?

Saclike structured that store materials like water, salts, proteins, and carbohydrates

it is bound by a singular membrane and found in plants

What's a lysosome ?

A spherical organelle that contains high concentrations of proteins. They also contain digestive enzymes which can break down ingested food in the vesicles. They can also break down organelles or whole cells.

What do microtubules do ?

Guide the movement of cell components. They help plant cells construct cell walls

What do microfilaments do ?

Line inside of plasma membrane to help animal cells maintain shape.

What is the cytoskeleton?

a microscopic network of protein filaments and tubules in the cytoplasm of many living cells, giving them shape and coherence.

What are the functions of life ?

Metabolism Reproduction Homeostasis Growth Response Excretion Nutrition

What is metabolism ?

all the enzyme-catalysed reactions occurring in a cell, including cell respiration

What is reproduction?

the production of offspring. It may be sexual or asexual

What is homeostasis ?

ability to maintain a constant stable internal environment

What is Growth ?

the permanent increase in size

What is response ?

the ability to respond to external or internal changes (stimuli) in their environment. Thus improving their chance of survival

What is excretion ?

the disposal of metabolic waste products, including carbon dioxide from respiration

What is nutrition ?

the acquisition of energy and nutrients for growth and development, either by, absorbing organic matter or by synthesising organic molecules (e.g. photosynthesis)

What adaptations allow these functions to occur ? ( Ribosomes and Mitochondria )

Mitochondria are present to provide energy through respiration

Ribosomes are present to produce proteins for growth and repair, in addition enzymes for vital cell functions

What adaptations allow these functions to occur ? ( Cell Membrane )

The cell membrane controls movement of materials in and out of the cell to maintain homeostasis

What adaptations allow these functions to occur ? ( Vacuoles and flagella )

Vacuoles are used for digestion purposes and also to store waste substance

Cilia or flagella are used for movement of the organism in response to changes in the environment

What subcellular structures have adapted to allow these functions to occur ?

• Mitochondria

• Ribosomes

• Flagella

• Vacuoles

• Cell Membrane

What characteristics allow paramecium to reproduce ?

The nucleus of the cell can divide to produce extra nuclei needed during reproduction ( asexual )

What characteristics allow paramecium to execrete ?

Waste products can diffuse out through the membrane

• allows entry if oxygen for respiration

What characteristics allow paramecium to maintain homeostasis ?

Contractile vacuoles at the end of each cell fill up with water and expel it through the plasma membrane.

• enables cell to maintain water levels

What characteristics allow paramecium to metabolise reactions ?

Reactions are metabolised in the cytoplasm.

• enzymes in the cytoplasm catalyse these reactions

What characteristics allow paramecium to grow ?

The food vacuoles contain smaller organisms that the paramecium has consumed. They are gradually digested and the nutrients are absorbed into the cytoplasm where they provide the energy needed for growth.

What characteristics allow paramecium to respond to stimuli ?

Beating of the cilia moves the paramecium through water. This can be controlled by the cell so that it responds to changes in the environment.

What are the types of eukaryotic cells?

fungus, protists, plants, and animals

Compare cell wall structure in eukaryotic cells

Animals: none Plants: cell walls composed of cellulose Fungi: cell walls composed of chitin

Compare vacuole structure in eukaryotic cells

Animals: small temporary vacuoles expel excess water or digest food / pathogens taken in by endocytosis Plants: used for storage of substances and pressurizing cell Fungi: used for storage of substances and pressurizing cell

Compare centrioles structure in eukaryotic cells

Animals: used to construct the spindle that moves chromosomes in mitosis Plants: none except in male gametes found at the base of flagellum Fungi: none except in male gametes found at the base of flagellum

Compare cilia and flagella structure in eukaryotic cells

Animals: present in many cells ( tail of male gametes ) Plants: none except in male gametes that swim using flagella Fungi: none except in male gametes that swim using flagella

Compare chloroplast structure in eukaryotic cells

Animal: none Plants: used for photosynthesis Fungi : none

What is undulipodia

flagella and cilia

What features of skeletal muscle make them atypical cells?

Multinucleate structures are formed when groups of cells fuse together ( Syncytium ). Muscle fibres develop to form columns of cells each with their own nucleus .

This goes against cell theory as the cell/fibre has more that one nucleus

What features of red blood cells make them atypical cells?

In mammals they do not have a nucleus in order to create more space for haemoglobin. Towards the end of their development in the bone marrow the nucleus is moved to the end of the cell and pinched off to be consumed by a phagocyte.

What features of phloem sieve tube elements make them atypical cells?

Xylem: made from columns of cylindrical cells in which dividing walls and typical structures are removed leaving a hollow tube that no longer consists of cells.

Phloem: Plasma membrane remains in the tube like structure but nucleus and other organelles break down.

Sieve tube elements are connected to companion cells in order to survive

What features of aseptate fungal hyphae make them atypical cells?

In some of the growing cells the nucleus keeps dividing without cell division occurring

Compare the number of nuclei in the atypical cells

Red blood cells: none Phloem sieve tube elements: none Skeletal muscle: many Aseptate fungal hyphae: many

What are examples of atypical cells

Red blood cells Phloem sieve tube elements: Skeletal muscle Aseptate fungal hyphae

What is symbiosis?

Any relationship in which two species live closely together

What is emdosymbiosis?

One organism ( endosymbiont ) lives inside another cell ( host )

Endosymbiont enters via endocytosis and lives inside a cell within the host

What is endocytosis ?

Process that cells use to make a vesicle or vacuole by pinching off the plasma membrane

Explain the origin of mitochondria within eukaryotes

Mitochondria once lived as prokaryotes that could perform aerobic respiration. Larger prokaryotes that could only respire anaerobically engulfed the mitochondria by endocytosis. They allowed the cells to live in the cytoplasm rather than killing them. Aerobic respiration in the endosymbiont ( mitochondria ) provided energy to the host more efficiently.

Natural selection therefore favoured cells with this endosymbiotic relationship.

• Mitochondria have evolved in eukaryotic cells today as they grew and divided as quickly as the host cell did.

Explain the origin of chloroplasts within eukaryotes

A prokaryote that had developed photosynthesis was taken in by a host cell and was allowed to grow and divide. This produces an endosymbiotic relationship again

What features of mitochondria and chloroplasts supports the endosymbiotic theory ?

• Double membrane ( expected if single membrane prokaryote was ingested by endocytosis )

• Own genes ( circular DNA molecule like that in prokaryotes )

• They transcribe their own DNA and use mRNA to synthesise their own proteins

• Ribosomes they use for protein synthesis have a size ( 70s ) similar to prokaryotes rather than eukaryotes

• Can only be produced by division of pre existing cells

What are the benefits of cell specialisation in multicellular organisms ?

The cells are more efficient as they only develop the features they need to carry out their functions

What are housekeeping genes?

Genes that are required in every cell in order to complete life sustaining activities

What is gene expression ?

The control of which genes act in a cell

What's the relationship between cell differentiation and gene expression ?

In differentiated cells different genes are switched on and expressed so the cell makes particular proteins and gene products

What organisms are multicellular ?

Plants, Animals, Fungi, Algae, Some prokaryotes

How has multicellularity evolved?

It has evolved independently more than once in the origins of plants and at least once in animals

Disadvantages of electron microscopes

• cannot view images in colour

• cannot view living cells

Light microscopes can do both of these things

State benefits of using fluorescent stains

• certain organelles can be viewed more vividly

Outline the process of using immunofluorescent technology to view specific proteins

Antibodies that bind to antigens in the cell are produced. Fluorescent markers of different colours are then linked to these antibodies. A multicoloured fluorescent image can then be produced showing where the different chemicals are located.

Outline the process of using freeze fracture electron microscopy to view images of cell surfaces

A sample is placed into liquefied propane at -190c so it freezes rapidly. A steel blade is used to fracture the frozen sample through the weakest points of the cells. Some of the ice is removed at the fractured surface by vaporisation ( etching ). A vapour of platinum or carbon is then fired onto the fractured surface which forms a coating producing a replica of the fractured surface.

• replica can be viewed under electron microscopes

Outline the process of visualizing specific proteins using cryogenic electron microscopy

A thin layer of pure protein solution is applied to a grid then flash frozen to create a smooth ice and prevent formation of water crystals. Liquid ethane just above its melting point ( -182.9c ) is usually used as the coolant. The grid is then placed in an electron microscope and detectors record the patterns of electrons transmitted by the individual protein molecules. The patterns are combined with computational algorithms to produce a 3D image of the molecules.

Why did cryo - EM change research ?

Previous methods only produced images of the proteins in their most stable form. Cyro - EM analyses the proteins at the time they froze in the water which allows scientists to research the change in protein forms as they carry out their functions.

Define resolution

The smallest distance between two objects that can be distinguished.

Define magnification

the ratio of an object's image size to its real size

Compare qualitative and quantitative observations.

Quantitative data is numerical and usually obtained with a measuring instrument whilst Qualitative involves descriptions that are more subjective