Cells as the Basis of Life Flashcards
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1
Q
In order to be considered living…
A
an organism needs to meet specific criteria (e.g. grow, reproduce, etc.)
2
Q
What is the smallest unit of structure and function in living things?
A
The cell
3
Q
Describe cell theory
A
- All living things are made of one or more cells. Every organism starts as one cell.
- Cells carry out the life processes of organisms. Metabolic processes in organisms occur within cells.
- All cells are derived from other cells. Cells contain hereditary material that is passed on via cell division.
4
Q
What are metabolic processes
A
Chemical reactions that occur within cells of organisms.
5
Q
What does the cell membrane do?
A
It separates the cell’s interior from the exterior environment. It controls movement of substances in and out of the cell (it is SELECTIVELY permeable).
It also provides attachment sites for the cytoskeleton (which keeps the cell’s shape and organisation)
6
Q
In terms of the cell membrane, proteins can:
A
- Transport substances through the membrane
- Facilitate signalling through the membrane
- Allow cell to cell recognition
- Allow intercellular joining
7
Q
Intercellular vs intracellular
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Intercellular is between cells, intracellular is within cells.
8
Q
How is the cell membrane a barrier if it’s a fluid?
A
The membrane is a fluid, but it can still act as a barrier because of its hydrophilic and hydrophobic structure.
9
Q
How are phospholipids arranged in the cell membrane?
A
They are arranged in a bilayer (meaning two) such that the hydrophobic tails are on the inside and the hydrophilic heads face outwards towards the water environment.
10
Q
What do cholesterol molecules do for the phospholipid bilayer?
A
Prevents from melting and freezing.
11
Q
Common features of ALL cells:
A
All cells arose from a common ancestor.
Modern cells are either prokaryotic or eukaryotic.
All cells have a cell membrane, cytoplasm, and ribosomes.
12
Q
Name the features of prokaryotes:
A
- Typically bacteria and archaea
- Contain ribosomes
- Contain one circular chromosome and can have additional small rings of DNA called plasmids
- Do not have a nucleus or other membrane bound organelles
- Most have a cell wall
13
Q
Name the features of eukaryotes:
A
- Typically all organisms apart from bacteria and archaea
- Contain membrane-bound organelles
- Contain ribosomes
- Only plants and fungi have cell walls (made of cellulose in plants and chitin in fungi)
14
Q
Describe the nucleus:
A
It has a double membrane called the nuclear envelope with nuclear pores.
Contains chromosomes made of chromatin.
Contains a nucleolus (site of rRNA production)
Outer membrane connects to the rough endoplasmic reticulum
15
Q
Describe the mitochondria
A
They manage the final stages of aerobic respiration (conversion of food molecules into usable energy as ATP)
Between 1 and several 1000 are in a cell depending on the type
Independently grow and reproduce in the cell
Have outer and inner membranes (double membrane)
The inner membrane is folded to have a large surface area
Has its own circular DNA
16
Q
Describe chloroplasts
A
The site of photosynthesis in eukaryotic cells
Have their own circular DNA
Are enclosed by a double membrane
Independently grow and reproduce within cell
17
Q
Describe the vacuole
A
It’s a fluid filled space bounded by a membrane
Has a function which varies depending on the cell
Mature plants have a large central vacuole for molecular/ion storage and structural support
Non-plant eukaryotic cells have smaller vacuoles
18
Q
Describe the rough endoplasmic reticulum
A
It is the membrane factory.
The site of protein synthesis (due to ribosomes being attached to the rough ER), modification and secretion
19
Q
Describe the smooth endoplasmic reticulum
A
Has diverse metabolic processes depending on cell type
Enzymes synthesis lipids like oils, phospholipids, and steroids like hormones (especially in adrenal glands)
Other enzymes help detoxify drugs and poisons especially in liver cells
20
Q
Describe the structure of the endoplasmic reticulum
A
It is a network of membranous tubules and sacs.
It channels molecules through the cell’s interior
Two distinct but connected regions that differ in structure and function (smooth and rough ER)
21
Q
Describe the golgi body (including vesicles)
A
The site of manufacture, collection (from ER), packaging, modification, storage and distribution of molecules (like proteins from ER) within and outside of cell
Comprises flattened membranous sacs
Is common in cells designed for secretion
22
Q
Describe ribosomes
A
Are the site of protein synthesis
Each is composed of 2 subunits of rRNA and proteins
Located freely floating in cytoplasm and bound to outside of rough ER and nuclear envelope
Are also found in mitochondria and chloroplasts
23
Q
Describe lysosomes
A
Animal cells contain small specific vacuoles, including lysosomes that contain enzymes for intracellular digestion/recycling.
24
Q
Difference between vacuole and vesicle
A
there is none.
25
Describe the cytoskeleton
The cytoskeleton is a network of different proteins that:
1. maintain and change cell shape and movement
2. provide anchorage and facilitate movement of organelles and chromosomes during cell division
26
Prokaryotic vs Eukaryotic
Prokaryotic:
- Generally smaller
- No membrane-bound organelles
- DNA in cytosol
- Circular chromosomes (DNA)
- Simpler internal organisation
- Only unicellular
Eukaryotics:
- Generally larger
- Membrane-bound organelles
- DNA in nucleus
- Linear chromosomes (DNA)
- Complex internal organisation
- Unicellular or multicellular
27
What do all cells require to grow, reproduce, repair and carry out their specific functions?
Energy.
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What is metabolism
All of an organism's chemical reactions (metabolic processes) are called its metabolism.
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How do organisms obtain their energy?
Life depends on the conversion of one energy form to another. Organisms obtain energy from their environment, either in physical (light) or chemical (molecular) form.
30
What is the main source of energy for life on earth?
The sun. Energy from the sun that goes into plants will eventually make it to other organisms through some means of transfer.
31
What are autotrophs?
Autotrophs PRODUCE the organic molecules that store chemical energy (like glucose) from inorganic substances (like CO2 or H2O), typically by photosynthesis.
E.g. plants
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What are heterotrophs?
Heterotrophs obtain their organic molecules that store chemical energy (like glucose) from consuming other organisms.
33
What is photosynthesis?
Photosynthetic organisms (plants, algae, some prokaryotes) convert light energy into chemical potential energy (organic molecules).
In eukaryotic cells this occurs in chloroplasts.
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What is the equation of photosynthesis?
6CO2 + 6H2O -> (light) -> C6H12O6 + 6O2
35
What is energy transformation in terms of cells?
The energy required to break bonds in a molecule like glucose is less than the energy needed to produce the bonds that form it. Therefore you get a net positive of energy from breaking glucose down.
Cells can release and use this energy by breaking down complex molecules.
This energy is temporarily stored in ATP molecules and some is released as heat.
36
What are the two types of cellular respiration?
Aerobic respiration (oxygen is present) and fermentation (oxygen is not present)
37
What is aerobic respiration and its equation?
The most common source of energy for cells in glucose, which is broken down via cellular respiration.
Aerobic respiration is represented as:
C6H12O6+6O2 -> 6CO2 + 6H2O
This is the exact opposite of the photosynthesis reaction.
38
Briefly state the process of aerobic respiration
Starting the cytosol, glucose and oxygen react to produce carbon dioxide and water. This forms ATP molecules and heat along the way.
It starts in the cytosol and finishes in the mitochondria.
39
What is glycolysis and an important feature about it?
Glycolysis is the step by step conversion in the cytosol of glucose to pyruvic acid. If O2 is present, pyruvic acid can be further broken down in the mitochondria into CO2 and water.
Each step in glycolysis is controlled by a specific enzyme producing an intermediate compound and some heat.
Essentially, this process involves many small steps.
40
Why do metabolic pathways in cells involve many small steps?
Many small steps will release small quantities of energy that can be trapped in ATP molecules (large quantities cannot be efficiently used)
The cell can use numerous different enzymes, allowing it to have various ways of controlling the metabolic pathway.
Large steps would create bad conditions (e.g. excess heat and acidity)
Small steps can provide useful intermediate compounds for other metabolic processes
41
What is fermentation and its equations?
Fermentation is an anaerobic (non-O2) variant of cellular respiration. It occurs in the cytosol ONLY.
Lactic acid fermentation:
C6H12O6 -> 2C3H6O3
Alcohol fermentation
C6H12O6 -> 2C2H5OH + 2CO2
C6H12O6 is glucose.
42
What is an example of aerobic respiration and fermentation being used?
If you’re physically exerting yourself too much that your cells don’t have enough oxygen for energy through aerobic respiration, purely glucose can be used in fermentation for energy which produces lactic acid, which gives a burning sensation.
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Endergonic vs exergonic reactions
Endergonic:
- Require an input of energy from the surroundings (store energy)
- Produce products that contain more potential energy than their reactants (photosynthesis)
Exergonic:
- release energy
- produce products that contain less potential energy than their reactants (cellular respiration)
Basically "build up" vs "break down"
44
What is ATP?
Adenosine triphosphate is a molecule made up of adenine, ribose and 3 phosphate groups.
Complex molecules (e.g. glucose) are broken down so that the energy is transferred to and stored in ATP molecules.
Energy stored in ATP can be used for almost all endergonic processes
45
Describe the ATP-ADP cycle
Bonds between the end phosphate groups of ATP can be broken by hydrolysis (breaking down using water). This converts ATP to ADP and is exergonic, releasing usable energy for cells.
Energy from breaking down complex molecules can then be returned to an ADP molecule along with a new end phosphate group, creating ATP again.
46
How do cells use ATP
Cells use the release of energy from the exergonic reaction of ATP to ADP for endergonic reactions that require an energy input.
47
What is diffusion?
The natural net movement of material from an area of high concentration to low concentration (moving down the concentration gradient).
This is passive and does not require energy.
Net diffusion will occur until the concentration gradient is gone (equilibrium of concentration)
48
What are the molecules that diffuse through cell membranes?
Gases (oxygen, carbon dioxide) easily travel through cell membranes (they are non-polar)
Water (small polar molecule) diffuse through aquaporins, which are channel proteins for water to go through hydrophobic membranes.
Large polar molecules, amino acids, and charged molecules are rejected
49
What is osmosis?
Osmosis is the net movement of water across a semi-permeable membrane towards a region of higher SOLUTE concentration. It is a type of diffusion and does not require energy.
Water will try to reach equilibrium when the solute cannot via diffusion, so water will always travel up the solute concentration gradient because it is going down its own concentration gradient.
50
In terms of osmosis, what is a hypotonic solution?
Where the solute concentration is lower outside the cell compared to inside.
Due to osmosis, this causes animal cells lyse and plant cells to become turgid.
51
In terms of osmosis, what is an isotonic solution?
Where the solute concentration is equal outside the cell and inside the cell.
Osmosis will not occur and the cells will remain normal.
52
In terms of osmosis, what is a hypertonic solution?
Where the solute concentration is higher outside the cell compared to the inside.
Due to osmosis, this causes animal cells to shrivel and plant cells to become flaccid.
53
What is facilitated diffusion?
Molecules that cannot easily diffuse through the phospholipid bilayer will passively pass through specific transport proteins down their concentration gradients.
Channel proteins provide a corridor for a specific molecule or ion.
Carrier/transport proteins change shape as a result of a specific solute binding to the protein.
These proteins are embedded in the cell membrane.
54
What is active transport?
Transport of solute material against the concentration gradient. This requires an input of energy from ATP and occurs at carrier proteins.
55
What is exocytosis?
Secretion of molecules via the fusion of vesicles with the cell membrane (from transport vesicles that have budded off from the Golgi body).
It requires energy input.
56
Endocytosis
Importing of molecules and other matter (e.g. bacteria & viruses) by the formation of new vesicles from the cell membrane
It requires energy input
57
What affects movement across membranes?
1. The concentration gradient
2. Temperature (molecules move faster in higher temp)
3. Surface area to volume ratio.
4. Type of molecule or ion being diffused
58
What single cell do all humans grow from?
The zygote. They grow into a complex system of organs, tissues and cells that have genetically identical DNA to that zygote.
(Remember cells are different because of gene expression and not their actual DNA)
The only time DNA would be different is a mutation or if they're gametes.
59
Describe binary fission
Prokaryotes divide to produce new cells by binary fission.
1. Circular chromosome is copied (DNA replication)
2. Each chromosome attaches to cell membrane at opposite ends of cell
3. Cell extends, pulling the two chromosomes apart
4. The cell divides into two daughter cells with identical DNA
60
Briefly describe the cell cycle
1. Interphase: Growth and DNA replication
2. Mitotic phase: Mitosis (division of nucleus and DNA) and cytokinesis (division of cytoplasm)
61
Describe the steps of interphase
G1: Growth of organelles and cell membrane, energy storage, etc.
S: Synthesis/DNA replication
G2: More growth, preparing for mitosis
62
What are the two ways eukaryotes can divide?
Mitosis: A cell dividing its DNA to form 2 identical cells
Meiosis: Production of gametes (e.g. egg and sperm cells), resulting in 4 cells with half the parent cell's genetic info
63
Describe the mitotic phase
G2: Last stage before mitosis, DNA has been replicated.
Prophase: Nuclear envelope disappears, chromatin condenses into chromosomes with sister chromatids, centrosomes move to ends of the cell and begin growing microtubules
Metaphase: Chromosomes align in the middle of cell, microtubules attach to chromosomes
Anaphase: Microtubules separate sister chromatids, moving them to opposite ends of the cell
Telophase: Mitosis is complete. Two daughter nuclei form and cytokinesis begins.
USE PMAT
Cytokinesis: Division of cytoplasm and formation of 2 separate cells. Chromatin becomes uncondensed.
64
How does mitosis differ in plant cells?
There are no centrosomes and vesicles fuse to form a new cell wall instead of cleaving cytoplasm.
65
What are stem cells?
Stem cells are constantly dividing to grow and replace old and damaged cells in multicellular bodies
Stem cells are undifferentiated cells that can produce new cells that undergo specialisation
66
What is cell cycle regulation?
Specific molecules in the cytoplasm determine if a cell can pass each checkpoint in the cell cycle.
Most body cells are unable to pass these checkpoints and will never divide
These cytoplasmic molecules are controlled by external and internal signals.
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In terms of cell cycle regulation, what are internal signals?
Internal signals report whether crucial cellular processes that should have occurred by that point have occurred.
E.g. the G1 checkpoint can is only passed (leads to DNA synthesis) if the cell has enough energy stored (ATP, glucose)
68
In terms of cell cycle regulation, what are external signals?
External signals report whether crucial environmental conditions are present.
Anchorage dependence: Normal cells only divide if anchored to a surface.
Density-dependent inhibition: Normal cells stop dividing when crowded.
Cancerous cells don't exhibit these signals.
69
Why is cell cycle regulation important?
Because loss of control can form cancerous cells, dividing excessively and invading other tissues.
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How can cell cycle regulation be bypassed?
Carcinogens can cause mutations in DNA, leading to formation of faulty proteins which don't properly control checkpoints.
Treatment of cancer uses chemotherapy drugs to interrupt the cell cycle.
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How do genetics differ between mitosis and meiosis?
Mitosis: Genetically identical daughter cells
Meiosis: Each of the 4 cells has half the parent cell's chromosomes. Gametes fuse during fertilisation to form a zygote (restoring them from their haploid no. of 23 to diploid no. of 46).
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How do eukaryotes asexually reproduce?
Some plants reproduce asexually by budding, creating bulbs, or sending out runners.
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How do eukaryotes sexually reproduce?
Haploid sex cells (gametes) are produced by meiosis
Gametes fuse (fertilise) to form diploid zygote
This results in higher genetic variation compared to asexual reproduction
74
Describe the human life cycle
Mitosis is for growth and repair, while meiosis is to reproduce
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Haploid vs Diploid
Haploid: Gametes (sperm or egg cells) contain half the number of chromosomes (23). This is called the haploid number.
Diploid: Somatic (body) cells contain the chromosomes from both the sperm and egg (46). This is called the diploid number.
76
Describe meiosis
Interphase: Before meiosis, DNA is replicated. If there is a pair of homologous chromosomes, they will be duplicated to have two sister chromatids (THEY ARE STILL 2 CHROMOSOMES)
Meiosis 1: Duplicated homologous chromosomes separate into different cells via process similar to mitosis.
Meiosis 2: Each chromosome separates its sister chromatids into different cells.
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What are homologous chromosomes?
Homologous pairs are pairs of chromosomes that have identical genes. One chromosome is from father and the other from the mother.
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How does genetic variation differ between mitosis and meiosis?
Mitosis results in two diploid daughter cells with identical genetic information.
Meiosis results in four haploid daughter cells with genetic variation.
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What causes the genetic variation from meiosis?
Independent assortment and crossing over.
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What is independent assortment?
When homologous pairs line up during Meiosis 1, they do it randomly.
Each pair lines up in an orientation that is independent of other pairs. This results in gametes with some chromosomes from the mother mixed with some from the father.
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What is crossing over?
During meiosis 1, homologous chromosomes pair up and line up, and non-sister chromatids exchange segments of DNA. This results in a mixture of maternal and paternal genetic information on each chromatid.
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Note about sister chromatids
Whether a chromosome has one or two sister chromatids, it is still ONE chromosome.
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What is cell culture?
Cell culture involves the growth of cells outside of their native environment. This allows scientists to easily study aspects of cell biology under controlled conditions without harming anything sentient.
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Cell culture conditions
- Sterile
- Suitable growth medium
- Suitable pH
- Suitable temp
- Oxygen (for aerobic respiration)
- Essential nutrients (e.g. glucose)
- Hormones/growth factors
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uses of cell culture
- Biotechnology
- Testing for mutagenic substances (instead of on animals)
- Researching biochemical processes (instead of on animals)
- Testing novel medicines (without harming animals)
- Tissue growth from stem cells to treat patients with tissue damage
- Creating clones (usually plants)
86
What are the limitations of cell culture?
Cell culture models lack physiological relevance, as monolayers of the same cell type poorly mimic the complexity of human tissues, organs and systems.
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Ethics of cell culture
Do we have the right to use cells, from a person that has died, for medical research?
