cells Flashcards
cells
what are the groups of eukaryotic cells?
-fungi
-animal
-plants
-protists
(algal and fungal cell are similar to plant cells)
what are the distinguishing features of eukaryotic cells?
- cytoplasm containing membrane-bound organelles
- so DNA enclosed in a nucleus
what are the structures found in animal cells?
- cell membrane
-mitochondrion
-nucleus
-ribosomes
-rough endoplasmic reticulum (RER)
-Smooth endoplasmic reticulum (SER)
-Golgi apparatus and vesicles
-lysosomes
what are the structures found in a plant cell?
- cell membrane
-mitochondrion
-nucleus
-ribosomes
-rough endoplasmic reticulum (RER)
-Smooth endoplasmic reticulum (SER)
-Golgi apparatus and vesicles
-lysosomes
-chloroplast
-cell wall
-cell vacuole
diagram of a plant and animal cell with labelled structures
describe the structure of the cell surface membrane
- found in all cells phospholipid bilayer embed within and attached on the outside (proteins, carbohydrates and cholesterol)
describe the function of the cell-surface membrane
- selectively permeable so enables control of passage of substance in/out of cell
-molecules/receptors/antigens on surface allows cell recognition/signalling
describe the structure of the nucleus
-nuclear envelope: double membrane that surrounds the nucleus - controls entry/exit of materials
-nuclear pores: allow passage of larger molecules
-nucleoplasm: granular, jelly like material that makes up the bulk of the nucleus
-nucleolus(dense region): site of rRNA production and makes ribosomes
-chromosomes(highly condensed)/ chromatin (condensed) : consists of protein/histone-bound, linear DNA
describe the function of a nucleus
- holds/stores genetic information which codes for polypeptide (proteins) in the form of DNA and chromosomes
-site of DNA replication - site of transcription (part of protein synthesis) producing mRNA
describe the structure of ribosomes
-not a membrane bound organelle
-made of ribosomal RNA and protein ( two subunits)- 80s found in eukaryotic cells, 70s found in prokaryotic cells
describe the function of a ribosome
- site of protein synthesis
describe the structure of rER and sER
-both have folded membranes called cisternae
-rER has ribosomes on cisternae (outer membrane)
-sER lacks ribosomes on surface, more tubular in appearance
- single membrane
describe the function of rER + sER
rER:
● Ribosomes on surface synthesise proteins
● Proteins processed / folded / transported inside rER
● Proteins packaged into vesicles for transport e.g.. to Golgi apparatus
sER:
● Synthesises and stores lipids and carbs
● E.g.. cholesterol and steroid hormones
describe the structure of Golgi apparatus and Golgi vesicles
-Golgi apparatus: flattened membrane sacs, has a single membrane
- Golgi vesicles: small membrane sac
describe the function of Golgi apparatus and Golgi vesicles
Golgi apparatus:
-modifies protein, e.g. adds carbohydrates to produce glycoproteins
- modifies lipids, e.g. adds carbohydrates to make glycolipids
- packages proteins/ lipids into Golgi vesicles
-produces lysosomes (a type of Golgi vesicles)
Golgi vesicles:
-transports proteins/lipids to their required destination
- e.g. moves to and fuses with cell-surface membrane
describe the structure of lysosomes
- bags of digestive enzymes
- has hydrolytic enzymes
- single membrane
describe the function of lysosomes
-release hydrolytic enzymes (lysozymes) to hydrolyse pathogens or worn out cell components (organelles) for reuse of materials
describe the structure of mitochondria
- double membrane that controls the entry/exit of material
- inner membrane is folded to form extension of cristae
- matrix: contains small ribosomes(70s) and circular DNA which allows the mitochondria to control the production of their own proteins
describe the function of mitochondria
- site of aerobic respiration
- to produce ATP for energy release (energy carrier molecule)
-e.g. for protein synthesis/vesicle movement/active transport
describe the structure of chloroplasts in plants and algae
- chloroplast envelope: double plasma membrane that surrounds the organelle- highly selective in what can be entered/exit the chloroplast
-grana: stacks of thylakoid(folded membrane embedded with pigments and is the 1st stage of photosynthesis)
-lamella: thylakoids linking grana
-stroma: fluid filled matrix where the 2nd stage of photosynthesis takes place. contains thylakoid membranes, small 70s ribosomes, circular DNA and within the stroma are a number of other structures e.g. starch granules and lipid droplets
describe the function of chloroplasts in plants and algae
- absorbs light energy for photosynthesis to produce organic substances e.g. carbohydrates/lipids
describe the structure of the cell wall in plants, algae and fungi
- composed mainly of cellulose ( a polysaccharide) in plants/algae
- composed of chitin ( a nitrogen-containing polysaccharide) in fungi
describe the function of the cell wall in plants, algae and fungi
- provides mechanical strength to cells
- so prevents cell changing shape or bursting under pressure due to osmosis
describe the structure of the cell vacuole in plants
a large shaped organelle that varies in shape containing cell sap
- single membrane
describe the function of the cell vacuole in plants
- maintains turgor pressure in cell (stopping plant wilting)
- contains cell sap - stores sugars, amino acids, pigments and any waste chemicals
describe how eukaryotic cells are organised in complex multicellular organisms
in multicellular organisms, eukaryotic cells become specialised for specific functions
- tissue: group of specialised cells with a similar structure working together to perform a specific function, often with the same origin
- organ: aggregations of tissues performing specific functions
- organ system: group of organs working together to perform specific functions
what are the distinguishing features of prokaryotic cells? and examples
- cytoplasm lacking membrane-bound organelles
-so genetic material not enclosed in a nucleus - prokaryotic organisms e.g. bacteria and archaea (always unicellular)
what are the structures that are sometimes present in a prokaryotic cell?
- capsule: additional protection, slimy layer made out of proteins which prevents cell from desiccating (drying out)
- plasmids: small rings of DNA
-flagella: rotates to enable the bacteria to move
what are the structures that are always present in a prokaryotic cell?
- cell surface membrane
- cell wall: contains murein, a glycoprotein
- cytoplasm
- small 70s ribosomes
- circular DNA: free in cytoplasm, not associated with proteins
compare and contrast the structure of eukaryotic and prokaryotic cells
- eukaryotic has membrane bound organelles e.g. mitochondria, ER but in prokaryotic there’s no membrane bound organelles e.g. no mitochondria and ER
- eukaryotic has a nucleus containing DNA but the DNA in prokaryotic is free in the cytoplasm instead
- eukaryotic: DNA is long and linear and associated with histone proteins
prokaryotic: DNA is short and circular and isn’t associated with proteins - eukaryotic has larger 80s ribosomes in cytoplasm. prokaryotic has smaller 70s ribosomes
- eukaryotic: cell walls only in plant, fungi and algae containing chitin or cellulose.
prokaryotic: all cells have cell walls containing murein, a glycoprotein - eukaryotic: plasmids/ capsules are never present (sometimes flagella)
prokaryotic: plasmids, flagella and capsules are sometimes present - eukaryotic: larger overall size
prokaryotic: smaller in overall size
describe why viruses are described as acellular and non-living
- acellular: not made of cells, no cell membrane/ cytoplasm/organelles
- non-living: have no metabolism, cannot independently move/respire/replicate/ excrete
describe the general structure of a virus particle
-nucleic acids surrounded by a capsid (protein coat)
- attachment proteins allow attachment to specific host cells
- no cytoplasm, ribosomes, cell wall, cell surface membrane etc.
- some also surrounded by a lipid envelope e.g. HIV ( not all viruses have a lipid envelope but HIVs do)
what’s the difference between bacterial capsules and virus capsids?
- bacterial (‘slime’) capsules provide protection and help with adhesion
- virus capsid (‘protein coat’) protect genetic material
how does prokaryotic cells make ATP?
has no membrane bound organelles so doesn’t have mitochondria but will still perform respiration to make ATP
what is cell fractionation used for?
-cells are broken open to release the contents and organelles are then separated
-used to isolate different organelles so they can be studied. This enables individual organelle structures and functions to be studied
-before cell fractionation can begin, the tissue is placed in a cold, buffered, isotonic solution
-there are 2 stages: homogenisation and ultracentrifugation
what happens in stage 1 of cell fractionation: homogenisation?
1.homogenise tissue/use a blender: disrupts the cell membrane, breaking open cells to release contents/organelles
2.placed in a cold, isotonic, buffered solution:
-cold: reduce enzyme activity so organelles not broken down/damaged
-isotonic: water doesn’t move in or out of organelles by osmosis so they don’t burst
- buffered: to keep pH constant so enzyme doesn’t denature
3. filter homogenate: remove large, unwanted debris e.g. whole cells, connective tissue
what happens in stage 2 of cell fractionation: ultracentrifugation
ultracentrifugation: separates organelles in order of density/mass
- centrifuge homogenate in a tube at a low speed
-remove pellet or heaviest organelle and respin supernatant at a higher speed
-repeat at increasing speeds until separated out, each time the pellet is made of lighter organelles (nuclei → chloroplast/mitochondria→ lysosomes → ER → ribosomes
what is the summarised stages of the cell cycle in the eukaryotic cell?
Stage 1:Interphase
-cell grows and organelles are synthesised
-DNA replicates semi-conservatively (S phase)
-Leading to 2 chromatids (identical copies) joined at a centromere
-chromosomes are not visible
-Number of organelles & volume of cytoplasm increases, protein synthesis (G1 / G2)
Stage 2: Mitosis
-Nucleus divides
-To produce 2 nuclei with identical copies of DNA produced by parent cell
Stage 3: Cytokinesis
-Cytoplasm and cell membrane (normally) divide
-To form 2 new genetically identical daughter cells
what happens in stage 1 of prophase?
- Nuclear envelope breaks down
-Chromosomes condense, becoming shorter / thicker so visible
○ Appear as 2 sister chromatids joined by a centromere - Centrioles move to opposite poles forming spindle network
what happens in stage 2 of metaphase?
-Spindle fibres attach to chromosomes by their centromeres
-Chromosomes align along equator
what happens in stage 3 of anaphase?
- Spindle fibres shorten / contract
- Centromere divides
- Pulling chromatids (from each pair) to opposite poles of cell
what happens in stage 4 of telophase?
- Chromosomes uncoil, becoming longer / thinner and are no longer visible
- Nuclear envelopes reform = 2 nuclei
-chromatids have reached opposite poles - Spindle fibres / centrioles break down
diagram of the different stage of cell cycle
why do some eukaryotic cells not undergo the cell cycle?
-within multicellular organisms, not all cells retain the ability to divide (e.g. neurons)
-Only cells that do retain this ability go through a cell cycle
Explain the importance of mitosis in the life of an organism
Parent cell divides to produce 2 genetically identical daughter cells for:
● Growth of multicellular organisms by increasing cell number
● Replacing cells to repair damaged tissues
● Asexual reproduction
Describe how tumours and cancers form
Mitosis is a controlled process so:
● Mutations in DNA / genes controlling mitosis can lead to uncontrolled cell division
● Tumour formed if this results in mass of abnormal cells
○ Malignant tumour = cancerous, can spread (metastasis)
○ Benign tumour = non-cancerous
Suggest how cancer treatments control rate of cell division
-Some disrupt spindle fibre activity / formation
○ So chromosomes can’t attach to spindle by their centromere
○ So chromatids can’t be separated to opposite poles (no anaphase)
○ So prevents / slows mitosis
-Some prevent DNA replication during interphase
○ So can’t make 2 copies of each chromosome (chromatids)
○ So prevents / slows mitosis
Describe how prokaryotic cells replicate
Binary fission:
1. Replication of circular DNA
2. Replication of plasmids
3. Division of cytoplasm to produce 2 daughter cells
○ Single copy of circular DNA
○ Variable number of copies of plasmids
Describe how viruses replicate
Being non-living, viruses do not undergo cell division
1. Attachment proteins attach to complementary receptors on host cell
2. Inject viral nucleic acid (DNA/RNA) into host cell
3. Infected host cell replicates virus particles:
a. Nucleic acid replicated
b. Cell produces viral protein / capsid / enzymes
c. Virus assembled then released
true or false: mitosis repairs cells?
mitosis creates new cells to replace damaged or dead ones, therefore
repairing the tissue, but not the cells themselves.
when does DNA replication occur?
in the interphase which is before mitosis
what are chromatids?
A chromatid is one of the two identical halves of a chromosome that
has been replicated. These are held together by a centromere.
what’s the difference between centromeres and centrioles?
Centromeres join sister chromatids, while centrioles are organelles
involved in spindle formation.
true or false: “Cytokinesis always happens.”
Some cells (eg. muscle cells) undergo mitosis (nuclear division) without
cytokinesis (cytoplasmic division), so have multiple nuclei.
true or false: “In binary fission in prokaryotic cells,
bacterial chromosomes replicate.”
Chromosomes consist of linear DNA associated with histones and are
only found in eukaryotic cells. Bacteria have circular DNA (no histones).
