2.4-2.6: Cell Structure Flashcards
What is the definition of a cell?
The basic unit of all living things
What is a eukaryotic cell?
A cell that contains a nucleus and makes up multicellular organs
What kind of organisms contain eukaryotic cells?
Fungis, animals and plants.
What is the definition of the “ultrastructure of a cell”?
Features that can be seen using an electron microscope
Where is the nucleolus?
Within the nucleus
Describe the nucleolus.
An organelle that doesn’t have a membrane, made up of DNA, RNA and proteins.
Describe the role of the nucleolus
Produces ribosomes by making RNA, which is used to produce Ribosomal RNA, which is combined with proteins to form the ribosomes
How are ribosomes produced?
The nucleolus makes RNA, which is used to produce Ribosomal RNA (rRNA), which is combined with proteins to form the ribosomes.
Describe the nucleus.
-Contians coded genetic information in the form of DNA molecules.
-Often the biggest organelle in the cell
-Surrounded by a nuclear envelope composed of two membranes
Describe the role of DNA in the cell
-DNA controls metabolic activities of the cell
-DNA directs the synthesis of all proteins required by the cell
-DNA encodes information
Where is DNA contained in the nucleus?
In the Nuclear envelope, within the double membrane, to protect it from damage in the cytoplasm
What does the nuclear envelope contain to allow molecules to move in and out of the nucleus?
Nuclear pores
What is the role of nuclear pores?
Within the nuclear envelope to allow molecules to move in and out of the nucleus
How are chromosomes created?
-DNA associates with proteins called HISTONES to form a complex called CHROMATIN
-The chromatin coils and condenses to form chromasomes.
What are histones?
Proteins found in the nucleus that provide structural support for chromosomes
What is chromatin?
Chromatin is a mixture of DNA and proteins that form the chromosomes
How does DNA leave the nucleus for protein synthesis?
-Because DNA is too large to leave the nucleus, it is transcribed into RNA molecules which can leave via the nuclear pores.
Why is DNA transcribed into RNA molecules?
Because the DNA is too large to leave the nucleus.
What are the mitochondria and their function?
-The site of the final stages of cellular respiration, that produce ATP (energy source)
-Contain their own DNA (mtDNA)
-Can produce their own enzymes and reproduce themselves.
What is the number of mitochondria in the cell a reflection of?
The amount of energy it uses.
Describe the structure of mitochondria.
-Mitochondria have a double membrane.
-Inner membrane is highly folded to form structures called CRISTAE
-The fluid interior is called the MATRIX.
-Inner membrane forming the cristae contains the enzymes used in aerobic respiration.
What are Cristae?
The structures formed by the highly folded inner membrane of a mitochondrion.
What is the matrix?
The fluid interior of a mitochondrion
What are vesicles?
-Membranous sacs that have storage and transport roles
-A single membrane with fluid inside
What is the role of a vesicle?
To transport materials inside the cell
What are lysosomes?
Specialised forms of vesicles that contain hydrolytic enzymes that break down molecules
What is the role of a lysosome?
-Break down waste material in cells, including old organelles.
-Responsible for breaking down pathogens ingested by phagocytic cells
-Also play an important in programmed cell death (apoptosis)
What is the cytoplasm?
-The medium for metabolic processes (catabolism and anabolism)
-Contains enzymes and cytosol
-Where chemical reactions for the cell take place
What chemical do you use to stain DNA?
Methylene blue
What is the cytoskeleton?
-A network of fibres necessary for the shape and stability of a cell, present throughout the cytoplasm
What is the function of the cytoskeleton?
-Holds organelles in place,
-Controls cell movement and movement of organelles within cells.
What are the 3 key components of the cytoskeleton?
Microfilaments, microtubules and intermediate fibres
What are microfilaments?
-A component of the cytoskeleton
-Formed from the protein actin
-Responsible for cell movement and cell contraction during cytokinesis
What is cytokinesis?
Where the cytoplasm is divided to form 2 daughter cells
What is actin?
Protein that forms microfilaments in the cytoskeleton
What are microtubules?
-A component of the cytoskeleton
-Polymerised tubes of globular tubulin proteins
-They form a scaffold-like structure that determines the shape of a cell
What are intermediate fibres?
-A component of the cytoskeleton
-Give mechanical strength to cells and help maintain their integrity
What are centrioles?
-A component of the cytoskeleton
-Composed of microtubules
-Two associated together form the centrosome
What are centrioles composed of?
Microtubules
What are centrosomes?
Cellular structures that separate chromosomes during cell division.
What are both the flagella and cilia made of?
Microtubules from the cytoskeleton
What are flagella?
-Whip-like extensions from the cell surface that are used for cell movement.
What are cilia?
-Hair-like extensions from the cell surface involved in creating currents
Which are longer: cilia or flagella?
Flagella
Which are found in greater numbers: cilia or flagella?
Cilia
What are actin and myosin?
-Microfilaments responsible for muscle contraction
What is the difference between actin and myosin?
-Actin is thinner and made of two polypeptides twisted around eachother
-Myosin is thicker and bobbly.
What does movement of the cytoskeleton by actin filaments cause?
Causes muscle cells to contract and allows cells to move.
Which organelles are involved in protein synthesis?
The nucleus, ribosomes, rough endoplasmic reticulum, and the golgi apparatus
What is the endoplasmic reticulum?
-A network of membranes enclosing flattened sacs called cisternae.
-Connected to the outer membrane of the nucleus
-Made up of two types: Smooth endoplasmic reticulum and rough endoplasmic reticulum.
What does the Rough Endoplasmic Reticulum do?
-Synthesises proteins
-Transports proteins made on attached ribosomes
What does the Smooth Endoplasmic Reticulum do?
-Is responsible for lipid and carbohydrate synthesis, and storage
What are the two types of endoplasmic reticulum?
Rough Endoplasmic Reticulum and Smooth Endoplasmic Reticulum
What is the golgi apparatus?
-A structure similar to the smooth endoplasmic reiticulum
-A stack of membrane bound, flattened sacs
What is the function of the golgi apparatus?
Modifies proteins and “packages” them into vesicles
(either vesicles if they leave the cell, lysosomes if they stay in the cell)
What are ribosomes?
-Small, dense organelles composed of 1 large subunit and 1 small subunit.
-Manufactured in the nucleolus from rRNA and protein
-The site of protein synthesis
-Can be free-floating in the cytoplasm or attached to ER, forming Rough ER.
What is the function of a ribosome?
They are the site of protein synthesis
-Act as an assembly line to use mRNA to assemble proteins
-Many ribosomes can read the same mRNA strand to create many copies of the polypeptide at the same time
How is Rough Endoplasmic Reticulum produced?
-Ribosomes are attached to endoplasmic reticulum
List the stages of protein production.
-Proteins are synthesised on teh ribosomes bound to the endoplasmic reticulum
-They then pass into its cisternae and are packaged itno transport vesicles
-Vesicles containing the newly synthesised proteins move towards the Golgi Apparatus through the transport function of the cytoskeleton
-Vesicles fuse with the face of the Golgi Apparatus and the proteins enter
-The proteins are structurally modified before leaving the Golgi Apparatus in vesicles from the opposite side
-Sensory vesicles carry proteins that are to be released fromt the cell, the vesicles fuse with the cell-surface membrane, releasing their contents by exocytosis
What structures are in a plant cell that aren’t in an animal cell?
-Permanent vacuole,
-Cell wall,
-Chloroplasts
What structures are in an animal cell that aren’t in a plant cell?
Centrosomes and lysosomes
What is the function of a plant cell wall?
-Surrounds the cell-surface membrane
-Gives the plant cell its shape
-Supports both the individual cell and the plant as a whole
-Acts as a defence mechanism
How does the plant cell wall act as a defence mechanism?
Protects contents of the cell against pathogens
What makes a plant cell rigid?
The contents of the cell push up against the cell wall
What is a plant cell wall made of?
Cellulose
How permeable is a plant cell wall
Freely permeable
What are vacuoles?
-Membrane-lined sacs in the cytoplasm containing cell sap.
What is the name of the membrane of the vacuole?
Tonoplast
State the functions of the vacuole.
-Acts as food store
-Accumulates waste products
-Maintains turgor in the plant cell
Is the tonoplast of the vacuole permeable?
It is selectively permeable, only some small molecules can pass through
What is the name of the vacuole that is exclusive to plant cells?
Permanent vacuole
Can animal cells have vacuoles?
Yes, but they are small and transient.
What are chloroplasts?
The organelles responsible for photosynthesis in plant cells.
Where are chloroplasts found in a plant?
In the cells of leaves and stems
What kind of structure do chloroplasts have?
Double membrane structure
What is the name of the fluid in the chloroplast?
The stroma.
What does the internal network of membranes in chloroplasts do?
Forms flattened sacs called thylakoids.
What is the name for several thylakoids stacked together?
A granum.
What are granum in the chloroplast joined together by?
Membranes called lamellae
What do grana in the chloroplasts contain?
The chlorophyll pigments, where light-dependant reactions occur during photosynthesis.
In chloroplasts, what is starch produced by photosynthesis present as?
Starch grains
What do chloroplasts contain?
membranes, DNA, and ribosomes
Because chloroplasts contain DNA and ribosomes, what are they therefore able to make?
Their own proteins.
What do internal membranes in the chloroplasts provide?
The large surface area needed for the enzymes, proteins and pigment molecules necessary for photosynthesis.
What did eukaryotic cells evolve from?
Less complex prokaryotic cells
When did prokaryotic cells first appear?
3.5 billion years ago
What are prokaryotic cells?
Cells without a nucleus
Describe the DNA of a prokaryotic cell.
-The structure is fundamentally the same as eukaryotes, but packaged diffferently
-They only have 1 molecule of DNA, a chromosome
Describe the chromosome of a prokaryotic cell.
-Only 1
-Supercoiled to make it more compact
-Genes on the chromosome are grouped into operons.
What type of ribosome do eukaryotes have, and why?
80S Ribosome, to make more complex proteins
What type of ribosome do prokaryotes have?
70S Ribosome
Compare the size of ribosomes in prokaryotic and eukaryotic cells.
Ribosomes in prokaryotic cells are smaller than ones in eukaryotic cells.
Describe the cell wall of prokaryotes.
-Made from peptidoglycan, aka murein. It is a complex polymer formed from amino acids and sugars.
Describe the structure of the flagella in prokaryotes.
-Thinner than the equivalent structure in eukaryotes and does not have the 9+2 arrangement
What is the eukaryote equivalent of flagella?
Cilia
How are flagella attached to the cell membrane of a bacterium?
By a basal body, attaching the filament of the flagellum to the cell-surface membrane.
What rotates the flagella?
A molecular motor, giving it a whip-like movement that propells the cell.
What provides the energy to rotate the flagella?
Energy produced from the process of chemiosmosis (the movement of ions)
What are plasmids?
Satellite DNA, which can replicate independant of the main chromosome.
What are mesosomes in a bacterial cell?
Inner extensions of the cell membrane, the site of respiration.
Define “endosymbiosis”
Symbiosis whereby one of the organisms lives inside the other.
