Cells Flashcards
Eukaryotic vs prokaryotic cells
- eukaryotic, animal/plant cell has membrane bound organelles
- prokaryotic, bacteria has no membrane bound organelles
2 forms of reproduction
- sexual reproduction, uses 2 parents, gametes combine to form zygote
- asexual reproduction, 1 parent to produce genetically identical offspring
Define stem cell
an unspecialised cell which can form into any other type of cell
How does a zygote develop into an organism
- zygotes are stem cells
- zygotes divide by mitosis to make many stem cells
- each stem cell differentiates into specialised cell
- each specialised cell divides by mitosis to make many copies and form a tissue
- different tissues join to form organs
- different organs join to form organ system
Define tissue, organ and organ system
- tissue = a group of specialised cells
- organ = made up of different tissues
- organ system = different organs working together
Structure of nucleus
- contains DNA
- ## DNA wrapped around histones to form chromatin
Difference between smooth and rough endoplasmic reticulums
- rough has ribosomes, makes proteins
- smooth has no ribosomes, makes lipids/carbohydrates
Role of golgi
modifies and packages proteins, packs them into vesicles for transport
Role of mitochondria
site of aerobic respiration, produces ATP
Structure of mitochondria
-double membrane, inner membrane folded into cristae (increases SA for enzymes of respiration)
- middle portion called matrix
Role of ribosomes
protein synthesis, attached to RER
Structure of chloroplast
- double membrane
- contains discs called thylakoids
- thylakoids contain chlorophyll
- stack of thylakoids called granum
- thylakoids surrounded by fluid called stroma
Features of bacteria
- no nucleus, loose DNA in single loops and plasmids
- no membrane bound organelles, smaller ribosomes
- contains cytoplasm
- contains cell membrane and cell wall
What is a virus made of
- DNA or RNA (if RNA, also has enzyme called reverse transcriptase which converts RNA into DNA)
- protein coat called capsid
- attachment proteins on outside
What is a chromosome
- DNA in coiled form
- formed during interphase of cell division
- made of 2 identical sister chromatids joined by centromere
- carries 2 copies of same DNA molecule
Define homogolous pair of chromosomes
a pair of chromosomes, 1 from mother, 1 from father, which carry same genes but different alleles
2 types of cell division
- mitosis; produces genetically identical cells for growth and repair of tissues
- meosis; produces genetically different haploid cells as gametes for sexual reproduction
What does mitosis produce
2 genetically identical diploid cells
Benefit of mitosis
growth and repair of tissues
Name the 3 stages of cell division
- interphase
- mitosis
- cytokinesis
What happens during interphase
- protein synthesis
- DNA replication
- organelle synthesis
Name the 4 stages of mitosis
- prophase
- metaphase
- anaphase
- telophase
Describe the process of mitosis
- Prophase; DNA coils to form chromosomes, nucleus breaks down, spindle fibres form
- Metaphase; chromosomes line up in middle of cell and attach to spindle fibre via centromere
- Anaphase; spindle fibres pull, centromere splits, sister chromatids move to opposite poles
- Telophase; chromatids uncoil, nucleus reforms (left with 2 genetically identical nuclei
What happens in cytokinesis
cell separates into two, each receives a nucleus and organelles/cytoplasm
What happens to DNA in mitosis
it halves
What happens to chromosome number in mitosis
stays the same (diploid)
What is cancer
formation of a tumour due to uncontrolled cell division/mitosis
How does uncontrolled cell division occur
- due to mutation of DNA
- mutation can only occur randomly or due to mutagens
- cancer cells are rapidly dividing cells
- so they have less time in interphase and more time in mitosis
Treatments for cancer
- surgery, aims to remove tumour
- radiotherapy, radiation used to destroy cancer cells
- chemotherapy, uses drugs which inhibit mitosis in rapidly dividing cells
What does meiosis produce
4 genetically different cells (haploid), half the amount of chromosomes
Benefit of meiosis
produces gametes which will be used in sexual reproduction in animals and plants
What are the stages of meiosis
- interphase
- meiosis I
- meiosis II
- cytokinesis
What happens in interphase
- protein synthesis
- DNA replication
- organelle synthesis
What happens in meiosis I
- prophase I, DNA coils to form chromosomes, nucleus breaks down, spindle fibres form, crossing over occurs
- metaphase I, homologous pair of chromosomes line up at centre of cell and attach to spindle fibre via centromere by random assortment
- anaphase I, spindle fibres pull, homologous pair of chromosomes separate to opposite sides by independent segregation
- telophase I, chromosomes uncoil, nucleus reforms
What happens in meiosis II
- prophase II, DNA coils to form chromosomes, nucleus breaks down, spindle fibres form
- metaphase II, chromosomes line up at centre of cell and attach to spindle fibres via centromere by random assortment
- anaphase II, spindle fibres pull, sister chromatids move to opposite sides by independent segregation
- telophase II, chromatids uncoil, nucleus reforms, left with 4 genetically different nuclei
What happens in cytokinesis (meiosis)
cell separates into 4, each receives a nucleus and organelles/cytoplasm
How does meiosis create variation
crossing over and independent segregation
What is crossing over
- occurs in prophase I of meiosis I
- homologous pair of chromosomes wrap around each other and swap equivalent sections of chromatids; produces new combination alleles
What is independent segregation
- occurs in anaphase I of meiosis I
- occurs in anaphase II of meiosis II
- produces a mix of alleles from paternal and maternal chromosomes in a gamete
What happens to DNA in meiosis
quarters
What happens to chromosomes in meiosis
number halves (haploid)
How do bacteria do cell division
- binary fission
- copy their DNA
- then separate into 2 new genetically identical bacteria (asexual reproduction)
Name 2 types of microscope
- light
- electron (TEM and SEM)
How do you judge a microscope
by magnification and resolution
What is magnification
how much larger the image size is compared to the actual size
Which has higher magnification
TEM>SEM>light
Formula for magnification
magnification= image size/actual size
Conversions
- 1mm= 1000 micrometres (pm)
- 1mm= 1000000 nanometres (nm)
Why can organelles appear different in images
viewed from different angles and at different levels
What is resolution
minimum distance at which two very close objects can be distinguished
Which has the highest resolution
TEM>SEM>light
Why do electron microscopes have a higher resolution
they use electrons which have a shorter wavelength
Advantages and disadvantages of TEM
- advantage; highest magnification and resolution
- disadvantages; can only observe dead specimens, specimen needs to be thin, black and white image, 2D image
Advantages and disadvantages of SEM
- advantage; produces 3D image
- disadvantages; can only observe dead specimens, black and white image
Describe cell fractionation
- break down tissue into cells by cutting a small sample and using a pestle and mortar
- add cold, isotonic, buffer solution to the sample
- homogenate the sample to break open cells releasing organelles
- filter the solution to remove large debris and inact cells
- add solution to a centrifuge, spin at low speed, heaviest pellet present at the bottom
Simple vs facilitated diffusion
- simple; molecules move directly through the phospholipid bilayer
- facilitated; molecules pass through transport proteins (large use carrier, charged use channel)
Factors that affect rate of diffusion
- surface area; increase= increase in ROD
- concentration gradient; increase= increase in ROD
- thickness
- temperature; increase means more kinetic energy, molecules move faster, faster ROD
- size of molecules; smaller = increased ROD
What is Fick’s law
(surface area x concentration)/thickness
Define osmosis
movement of water molecules from an area of high water potential to an area of low water potential through a partially permeable membrane
Which liquid has the highest water potential
distilled water
What happens if you surround an animal cell with pure water
cell swells and bursts due to osmosis
What happens if you surround a plant cell with pure water
swells but doesn’t burst, becomes turgid, cell wall prevents it from bursting since cellulose is a strong material
What happens if you surround an animal cell with concentrated sugar/salt solution
cell shrinks, water leaves by osmosis
What happens if you surround a plant cell with concentrated sugar/solution
water leaves by osmosis, cell wall prevents cell from shrinking, keeps it rigid, cell is plasmolysed
Define active transport
movement of molecules from an area of low to high concentration against a concentration gradient using ATP and carrier proteins
Describe the process of active transport
- molecules in area of low concentration bind to carrier protein
- ATP breaks down to ADP and Pi and energy
- the Pi and energy cause carrier protein to change shape
- carrier protein releases molecules on opposite side in area of high concentration
- carrier protein releases the attached Pi to return to its original shape
Enzymes of carbohydrate digestion
- amylase; converts starch/glycogen into maltose
- maltase on lining of small intestine; converts maltose into glucose
- lactase on lining of small intestine; converts lactose into glucose and galactose
- sucrase on lining of small intestine; converts sucrose into glucose and fructose
Where can amylase be found
salivary gland and pancreas
Enzymes of protein digestion
- endopeptidase in stomach; hydrolyses peptide bonds in middle of polypeptide chain into smaller chains
- exopeptidase in small intestine; hydrolyses peptide bonds at end of chains to leave dipeptides
- dipeptidase on lining of small intestine; hydrolyse dipeptides into amino acids
Enzymes of lipid digestion
lipase in small intestine leaves monoglyceride and 2 fatty acids
Adaptations of small intestine for absorption
- cells lining SI have microvilli which increase surface area
- wall of SI is thin, short diffusion distance
- rich blood supply, maintains concentration gradient
- cells lining SI have transport proteins, enzymes and many mitochondria
Describe the absorption of glucose and amino acids in the SI
- sodium ions are actively transported from cells lining SI into the blood
- this lowers the sodium ion concentration in the cell
- therefore sodium ions move from lumen of SI to the cell
- this pulls in glucose and amino acids via a cotransport protein
- therefore glucose and amino acids build up in the cell and move into blood via diffusion
Describe the absorption of monoglyceride and fatty acids
- lipids emulsified by bile into micelles
- micelles digested by lipase into monoglyceride and 2 fatty acids
- monoglyercide and fatty acids absorbed by cells lining SI by simple diffusion
- this forms a chylomicron which enters the blood
What is lactose intolerance
- person doesn’t produce lactase enzyme
- lactose remains undigested
- leads to diarrhoea and flatulence
What is a pathogen
a microorganism which causes disease
Examples of pathogens
virus, bacteria, fungi
How do bacteria cause disease
by producing toxins
How do viruses cause disease
by dividing inside cells causing them to burst
Name the body’s 3 forms of defence against pathogens
- barriers
- phagocytes
- specific response
Name examples of a barrier
- skin, an impermeable barrier
- mucus and cilia in lungs
- stomach acid denatures pathogens
Describe the process of phagocytosis
- pathogen releases chemicals
- this attracts the phagocyte
- phagocyte binds to the pathogen
- phagocyte englufs the pathogen
- this forms a phagosome around the pathogen
- lysosomes inside the phagocyte release digestive enzymes into the phagosome
- this breaks down the pathogen by hydrolysis
Describe the cell-mediated response
- phagocytes perform phagocytosis without destroying the antigen, they place antigens on their surface
- t cells bind to the antigen and become stimulated
- they divide by mitosis to form 3 types of cells, t helper, t killer and t memory
- t helper cells stimulate b cells
- t killer cells kill infected cells
- t memory cells provide long term immunity
Role of t helper cells
stimulate b cells
Role of t killer cells
kill infected cells
Role of t memory cells
provide long term immunity
Describe the humoral response
- b cells engulf and present antigens on their surface
- t helper cells bind to this
- b cells become stimulated and divide by mitosis to form plasma cells and b memory cells
- plasma cells produce antibodies
- b memory cells provide long term immunity
Role of plasma cells
produce antibodies
Role of b memory cells
provide long term immunity
What is an antigen
a protein on the surface of a pathogen that stimulates an immune response
How does the immune response lead to the production of antibodies
- phagocytes stimulate t cells
- t cells form t helper cells
- t helper cells stimulate b cells
- b cells form plasma cells
- plasma cells make antibodies
What is an antibody
a protein specific to an antigen secreted by plasma cells
How do memory cells work
if a person is reinfected with the same pathogen, memory cells recognise the pathogen, produce antibodies rapidly and to a large amount
How does a vaccine provide immunity
involves giving an injection that contains dead/weakened pathogens that carry antigens which stimulate the immune response leading to the production of antibodies and memory cells
Active vs passive immunity
- active; person has memory cells, makes their own antibodies and provides long term immunity
- passive; person given antibodies, these work then die, no long term immunity, no memory cells
How does active immunity occur
- naturally; by primary infection
- artificially; vaccination
How does passive immunity occur
- naturally; from mother to baby
- artificially; by injection
Features of a successful vaccination programme
- produce effective vaccine, makes memory cells without major side effects
- low cost
- easily produced
- herd immunity
What is herd immunity
when a large proportion of the population is vaccinated so most people will be immune, increases chance of non-immune person coming into contact with immune, so pathogen won’t spread
What is antigenic variability
pathogen mutates, antigen changes shape so memory cells no longer complementary, so pathogen can reharm
Describe how HIV is replicated
- attachment protein attaches to receptors on t helper cell
- RNA enters cell
- reverse transcriptase converts RNA into DNA
- enzymes are produced
- virus particles are assembled then released
Describe how HIV is replicated once inside a T helper cell
- RNA is converted into DNA using reverse transcriptase
- DNA is inserted into t helper cell’s nucleus
- DNA is transcribed into HIV mRNA
- HIV mRNA is translated into new HIV
