Topic 2: Cells Flashcards
How are Eukaryotes characterised?
They are characterised by the presence of a nucleus and cytoplasm containing many cell organelles e.g. mitochondria and endoplasmic reticulum.
What is the structure and function of a Nucleus?
Function: -The Nucleus contains the genetic material, DNA, which determines the cell’s development, structure, and function. The nucleus also controls protein synthesis and therefore, controls the development and function of a cell.
Structure: -The nucleus is bound by a double membrane, the nuclear envelope which has nuclear pores allowing communication with the cytoplasm.
–>Chromatin is made up of DNA coiled around proteins called histones. (Linear molecule)
What is the structure and function of Ribosomes?
-Ribosomes are very small organelles, made up of protein and ribosomal RNA (rRNA)
-They are present in the cytoplasm or attached to the RER
-Function: -Used in protein synthesis, joining amino acids.
What is the structure of the Endoplasmic reticulum?
-RER (Rough Endoplasmic Reticulum) has ribosomes that produce secretory proteins, which are proteins released out of the cell.
-(These secretory proteins are sent to the Golgi apparatus for modification and/or packaging.)
-SER (Smooth Endoplasmic Reticulum) lacks ribosomes and is involved in the production and transport of lipids.
What is the structure and function of the Golgi apparatus and the Golgi vesicle?
-The Golgi apparatus consists of flattened, membrane sacs:
–>Adds carbohydrates to proteins received from RER to form glycoproteins
–>Packages proteins/glycoproteins into Golgi vesicles for secretion
–>Produces lysosomes, a type of Golgi vesicle that releases lysozymes (hydrolytic enzymes)
-The Golgi apparatus is abundant in secretory cells e.g. in the pancreas.
What are Lysosomes and what is their function?
-Lysosomes are simple sacs containing hydrolytic enzymes surrounded by a single membrane. (The enzymes are kept away from the rest of the cell or they would destroy it)
-(They are made in the Golgi apparatus)
-Function:
1) Digestion of material taken in by phagocytosis (by fusing with the vesicles formed during phagocytosis and releasing hydrolytic enzymes)
2) Non-functioning organelles within the cell may be engulfed and digested within lysosomes.
3) Release of enzymes outside the cell (sometimes)
What is the function of Mitochondria?
Mitochondria are involved in aerobic respiration, which produces ATP
-(They are variable in shape and size but are often rod shaped)
What is the function of Chloroplasts?
Chloroplasts perform photosynthesis.
What additional structures do plant cells have that animal cells don’t?
1) Cell wall –>providing support, strength, and shape of the cell. the cell wall consists of cellulose microfibrils (which provide strength).
2) Chloroplasts (containing the pigment chlorophyll)
3) A large vacuole–> containing soluble sugars, salts and sometimes pigment. (The membrane surrounding the vacuole is known as the tonoplast)
How are Epithelial cells from the small intestines adapted to their function?
They are specifically adapted for the absorption of digested food products:
–>The cell surface membrane is folded into microvilli providing a large surface area for the absorption of digested foods
–>Numerous mitochondria provide energy in the form of ATP for the active uptake of digested food molecules.
What are Prokaryotes?
Bacteria are prokaryotes and are single-celled organisms with no nucleus and no membrane-bound organelles in their cytoplasm.
What do Prokaryotes always and sometimes contain?
Always:
–>Cell wall
–>Cell surface membrane
–>Circular DNA molecule that is free in the cytoplasm (and not associated with protein)
–>Ribosomes
–>Cytoplasm
Sometimes:
–>Capsule (surrounding the cell wall)
–>Plasmids (one or more)
–>Flagella (one or more)
What are the differences between Prokaryotic cells and Eukaryotic cells?
-P-No nucleus (E-Nucleus present)
-P-No membrane bound organelles present (E-Present)–>e.g. Mitochondria/RER/SER/Golgi Body etc.
-P-Smaller 70s ribosomes (E-Larger 80S ribosomes)
-P-DNA is circular (E-DNA is linear)
-Murein cell wall (E-Cell wall, if present does not contain Murein)
What is a Virus and what are its characteristics?
Viruses are acellular and non-living
They have:
–>No nucleus/Organelles/Cell surface membrane/cytoplasm
-A typical virus particle will always contain genetic material (DNA/RNA), a capsid (consisting of protein) and attachment proteins on the outside.
What is Centrifugation?
The process of separating structures with different densities.
The process works by spinning the sample at high speeds in a centrifuge, which generates a strong force that causes particles to sediment or separate according to their size, shape, and density. This technique is commonly used in biological and chemical laboratories to separate substances like cells, organelles, proteins, or blood components.
How is a sample of cells prepared for centrifugation?
–>The cells are broken down by grinding (Homogenising) tissue such as the liver in an ice-cold, isotonic, buffer solution using a blender.
–>Isotonic solution prevents the osmotic movement of water in or out of organelles (which may cause them to burst or shrivel)
–>Ice-cold (i.e. low temperature) prevents the action of enzymes within the cells that may cause self-digestion (autolysis) of the organelles
–>A buffer solution will maintain the pH so that the proteins (particularly the enzymes) are not denatured.
How is centrifugation carried out?
1) The suspension is filtered to remove cell debris (such as cell walls or any cells which have not burst)
2) Centrifuge homogenate at low speed, the densest organelles i.e. the nuclei will form a pellet (sediment) at the bottom of the test tube.
3) The supernatant liquid is spun at a higher speed
4) Repeat the process, increasing the speed and duration of centrifugation to obtain a series of pellets containing organelles of decreasing density.
5) Isolate the organelles in order, nuclei chloroplasts; mitochondria; ER; and ribosomes.
Compare Light Microscopes to Electron Microscopes
Electron:
-Uses beams of Electrons
-Much greater resolution
-Focused using magnets
-Much greater detail (/much smaller structures visible)
-Specimens must be dead and dehydrated
-Image is not in colour
-Preparation of specimens is very complex and time-consuming
Light:
-Uses beams of Light
-Relatively low-resolution
-Focused using glass lenses
-Much lower detail (/smaller structures not visible)
-Specimens can be living (movement can be observed)
-Image in colour
-Preparation of specimens is relatively quick and easy.
What are the 2 types of electron microscopes?
Transmission Electron Microscope (TEM): (Internal)
In TEM, electrons are transmitted through a very thin specimen. The electrons interact with the sample, and an image is formed based on how the electrons pass through or are scattered by the material. TEM provides high-resolution images of internal structures of cells, tissues, and materials at the nanometer scale.
Scanning Electron Microscope (SEM): (external)
In SEM, a focused beam of electrons is scanned over the surface of the sample. The electrons interact with the atoms on the sample’s surface, producing secondary electrons that are detected to form an image. SEM provides detailed 3D surface images of the sample, allowing for high magnification of surface features.
What are the advantages and disadvantages of TEMs?
TEM:
(+)
–>High Resolution: TEM provides extremely high resolution, allowing observation of internal structures at the atomic.
–>Detailed Internal Imaging: It can produce detailed cross-sectional images of thin samples, revealing the internal structure of the sample.
(-)
–>Sample Preparation: TEM requires very thin samples (often less than 100 nm), which can be time-consuming and challenging to prepare. Biological samples may require complex staining and fixation processes.
–>Complex Operation: TEM is more technically demanding and requires more specialized knowledge to operate effectively and interpret results.
–>Vacuum Requirement: Like all electron microscopes, TEM requires a vacuum environment, which means that only certain types of samples (especially biological ones) can be studied after special preparation.
What are the advantages and disadvantages of SEMs?
SEM:
(+)
–>Surface Imaging: SEM provides high-resolution, 3D-like images of the surface of samples, which is ideal for examining the morphology of objects like cells, materials, and nano-structures.
–>Speed and Accessibility: SEM generally requires less time for sample preparation and can be easier to use for many types of samples compared to TEM. It’s a good choice for quick analysis of surface features.
–>Depth of Field: SEM has a large depth of field, which allows for detailed imaging of rough and uneven surfaces without losing focus.
(-)
–>Lower Resolution: SEM has a lower resolution than TEM, typically in the range of 1–10 nanometers, which makes it less suitable for viewing internal structures at atomic scales.
–>Surface Only: SEM provides detailed images of the sample’s surface but cannot directly examine internal structures without special preparation, such as making thin sections or using techniques like focused ion beam (FIB) milling.
–>Damage to Samples: As with TEM, SEM can also damage samples with the electron beam, though generally less severely, and the damage can be mitigated by reducing the beam intensity or using cryo-SEM for biological samples.
What is mitosis?
Mitosis is a type of nuclear division that produces genetically identical cells. (during mitosis the parent cell divides to produce 2 daughter cells, each containing an exact copy of the DNA in the parent cell.
What happens in Interphase?
-DNA content is doubled via DNA replication
-(Increase in protein synthesis)
-Cell organelles are replicated e.g. mitochondria and ATP content is increased (as cell division is an active process)
How many stages does the cell cycle have?
The cell cycle has 3 stages:
1) Interphase–>represents the non-dividing cell when cell growth occurs
2) Nuclear division–>nucleus divides into 2 (mitosis)
3) Cytokinesis–> cytoplasm divides into 2 (mitosis)
What happens in Prophase? (1)
-Chromatin Condensation: Chromatin fibres condense into visible chromosomes, each consisting of two sister chromatids joined at the centromere.
-Nuclear Envelope Breakdown: The nuclear envelope begins to disintegrate, allowing spindle fibres access to the chromosomes
-Spindle Formation: The mitotic spindle, a structure made of microtubules, starts to form from the centrosomes, which move to opposite poles of the cell.
-Nucleolus Disappearance: The nucleolus fades as the cell prepares for division.
What happens in Metaphase? (2)
-The centrioles in animal cells form a spindle across the cell. (the spindle consists of protein microtubules)
-Each chromosome moves to the equator of the spindle and attaches to it via its centromere
(Sister chromatids are orientated towards opposite poles of the cell)
What happens in Anaphase? (3)
-The centromere splits and the sister chromatids separate
-The spindle microtubules pull Sister Chromatids to opposite poles of the cells.
What happens in Telophase? (4)
-Chromatids are at opposite poles and now start to uncoil.
(Nuclear membrane also reforms)
–>The 2 cells are genetically identical to each other and to the original parent cell.
What is Cytokinesis?
The splitting of the cytoplasm into 2. (2 new cells form as a cell-surface membrane and in plants, a cellulose cell wall forms)
What is Cancer?
-Cancer is a group of diseases caused by uncontrolled growth and rapid division of cells. (often results from mutation to the genes that regulate mitosis and the cell cycle).
How is Cancer treated?
Cancer treatments often include drugs to inhibit the enzymes, DNA helicase and DNA polymerase (both important in DNA replication) or to inhibit spindle formation.
How do prokaryotes reproduce?
Prokaryotes mainly reproduce by asexual reproduction by a process called Binary Fission (Where one cell divides into 2 daughter cells)
-It includes:
–>replication of the circular DNA and of plasmids
–>division of the cytoplasm to produce 2 daughter cells, each with a single copy of the circular DNA and a variable number of copies of plasmids.
What is the process of Binary Fission?
1) Cell elongates and DNA is replicated
2) Cell wall and plasma membrane begin to divide
3) Cross-wall forms completely around divided DNA
4) Cells separate
