Topic 3 Flashcards
Eukaryote cell diagram
Ngng
Organelles
Parts of the cell
Nucleus
Nuclear envelope = double membrane
Chromatin = DNA + protein
Nucleolus = makes ribosomes
Nuclear Pore = allows movement between nucleus & cytoplasm
Controls cell activities via controlling DNA transcription
Lysosome
Round organelle with membrane
Contains digestive enzymes (seperayed from cytoplasm due to membrane)
- digest invading cells
- break down old cell components
Ribosome
Very small Floats free or attached to rough endoplasmic reticulum No membrane Made of protein + RNA Comprised of small + large subunit
Site where proteins are made
Rough endoplasmic reticulum (RER)
System of membranes
- fluid filled space
- covered with ribosomes
Folds + processes proteins made at ribosomes
Smooth endoplasmic reticulum (SER)
System of membranes
- fluid filled space
Synthesises and processes lipids
Centriole
Small hollow cylinders made IP of microtubules (tiny protein cylinders)
Chromosome separation
- cell division
Somewhat star shaped
Golgi Apparatus
System of fluid filled, membrane bound, flattened sacs
- vesicles seen at edges
Processes + packages new lipids & proteins
Makes lysosomes
Mitochodrion
Oval shaped Double membrane - inner = folded = cristae Inside = matrix - enzymes involved in respiration
Site of aerobic respiration
ATP produced
Found in large numbers in very active cells
Protein production & transport
- Proteins made at ribosomes
- ribosomes on RER make proteins that are excreted or attached to the cell membrane
- free ribosomes in the cytoplasm make proteins that stay in the cytoplasm - New proteins produced at RER are folded + processed in the RER
- RER -> golgi apparatus via vesicles
- Golgi apparatus: may undergo further processing
- Proteins -> vesicles
- transported around cell
- or, extracellular enzymes move to cell surface to be excreted (exocytosis)
Prokaryotic cell diagram
Ngngn
Prokaryotic cells
Cytoplasm = no membrane bound organelles
Ribosomes = smaller than eukaryotic ones
Plasma membrane = protein + lipid bilayer
Cell wall = support (prevents shape change)
- polymer = MUREIN (glycoprotein)
Pili = short hairs
- stick to cells
- transfer genetic material
Capsule = secreted slime (bacteria)
- protects against immune attacks
Mesosome = inwards folds in plasma membrane
- either site of respiration
- or artefacts produced when preparing for microscopic viewing
Plasmids = small loops of DNA
- genes for antibiotic resistance
- pass between pokaryotes
- not always present
Circular DNA = free floating (coiled strand)
- no his tone protein attached
Flagellum = rotating hair like structure (movement)
- not all have
Tissues
Group of similar cells especially adapted to work together to carry out a particular function
Squamous epithelium
A single layer of cells lining a surface
E.g. aveoli on lungs
Cells are accompanied by a basement membrane to anchor them
Ciliated epithelium
Layer of cells covered in cilia
Found where movement is required
E.g. tranchea
Xylem tissue
Transports water around plant
Supports plant
- xylem vessel cells (thickened walls perforated by pits)
- parenchyma cells (fills in gaps between vessels)
Cartilidge
Type of connective tissue Found in joints Shapes + supports - ears - nose - windpipe
Two cells trapped together
Surrounded by a fibre filled matrix
Mitotic Index
Proportion of cells undergoing mitosis
(No. of cells with visible chromosomes)/(total no. of cells observed)
High = lots in mitosis e.g. plant root tip
Organs
Group of different tissues that work together to perform a particular function
Leaf
Lower epidermis = stoma to let air in/out for gas exchange
Spongy mesophyll = spaces to let gas circulate
Palisade mesophyll = photosynthesis
Xylem = carries water to leaf
Phloem = carries sugar away from leaf
Upper epidermis = covered in waterproof waxy cuticle
- reduced water loss
Lungs
Squamous epithelium = surrounds the aveoli
Fibrous connective = helps force air back out of the lungs when exhaling
Endothelium = makes up wall of capillaries (surrounds aveoli)
- lines the larger blood vessels
Mitosis
Parent cell divides -> two genetically identical daughter cells
Growth, repair & asexual reproduction
Part of cell cycle:
- cell growth & DNA replication = Interphase
- mitosis is after interphase
5 stages of Mitosis
- Interphase
- Prophase
- Metaphase
- Anaphase
- Telophase
Interphase
Cell carries out normal function + prepares to divide
Cell’s DNA unravels + replicated
Organelles also replicated -> spare ones
ATP content increased
3 stages: G1, S, G2
Note: chromosomes = two chromatic strands joined in middle via centromere
- two strands as genetic copy made during interphase
Gap phases 1 (G1)
Cells grow
New organelles made
Gap phase 2 (G2)
Cell keeps growing
Proteins needed for division are made
Synthesis (S)
Cell replicates DNA
Prophase
Chromosomes condense -> shorter + fatter Centrioles move to opposite ends of cell - network of protein fibres formed across cell = spindle Nuclear envelope breaks down - chromosomes lie free in cytoplasm
Metaphase
Chromosomes (each = two chromatids) line up along the middle of the cell
Attach to spindle via centromere’s
Anaphase
Centromeres divide
-> separates each pair of sister chromatids
Spindles contract
-> chromatids pulled to opposite poles of the spindle (centromere first)
- chromatids appear v-shaped
Telophase
Chromatids reach opposite poles on the spindle
-> uncoil -> long + thin = chromosomes
Nuclear envelope forms around each group of chromosomes
-> two nuclei
Cytoplasm divides (cytokinesis) -> two daughter cells
Gametes
Male & female sex cells
- join together at fertilisation (exact moment the nuclei fuse)
- males = sperm
- female = ova
- 23 chromosomes (one set)
- offspring = genetically unique
Ova (mammalian gamete)
- much larger than sperm
- contain huge food reserves to help nourish developing embryo
Follicle cells (protective coating) Zona pellucida = protective glycoprotein layer sperm need to penetrate Cell membrane (attached to which is sperm receptors) Cortical granules (triggers thickening of ZP) Nucleus
Sperm (mammalian gamete)
- respiration takes place in mitochondria (energy = ATP)
- pointed head with tail shape
Acrosome (in head tip) = digestive enzymes required to break down zona pellucida -> penetration
Nucleus (in head)
Cell membrane (surrounds head)
Mitochondria (in between head and flagellum) = lots required for energy to swim
Flagellum = allows swimming
Fertilisation in mammals
- sperm deposited high in vagina, close to cervix entrance
- make their way up the cervix -> uterus -> oviduct
- in the oviduct -> fertilisation
- swim to egg cell
- contact zona pellucida
- acrosome reaction (digestive enzymes released)
- digest zona pellucida - one sperm moves to cell membrane
- head fuses with membrane
- triggers cortical reaction - egg cell releases contents of vesicles (cortical granule) into space between membrane and ZP
- ZP thickens (impenetrable)
- > only one sperm fertilises - nucleus enters -> tail discarded
- gametes fuse (nuclei)
Female sex organs diagram
ngng
Acrosome reaction diagram
ngng
Meiosis
Gametes = genetically different
- DNA replicates -> chromatids (x2)
- DNA condenses -> double armed chromosomes
= sister chromatids
3, chromosomes arrange in homologous pairs - first division = pairs separated -> 1/2 chromosome number
- second division = pairs of sister chromatids separated
- four new genetically different daughter cells = gametes
Meiosis creates genetic variation via:
- Crossing over chromatids
2. Independent assortment of chromosomes
Crossing over chromatids
- Before meiosis’s 1st division, homologous pairs of chromosomes pair up
- Two of the chromatics in each homologous pair twist around each other
- Twisted bits break off from original chromatic & rejoin onto the other chromatic -> genetic material recombined
- Chromatics = same genes, different allele combos
-> 4 new daughter cells = chromatics with different alleles
Independent assortment of chromosomes
- Daughter cells (4) = different chromosome combos
- Half paternal, half maternal = all cells
- Different combos of maternal + paternal chromosomes go into each cell
- Independent assortment = separation
Linked genes
Position of gene on chromosome = locus
- independent assortment
- > genes with loci on different chromosomes end up randomly distributed in gametes
Genes with loci on same chromosome = linked
- stay together during IA
- passed into offspring together (unless crossed over)
Closer together gene’s loci on chromosome:
- closer link
- less likely to be split up
Locus
Position of gene on chromosome
Sex-linked charecteristics
= Locus of allele on sex chromosome
Female = xx Male = xy - y < x (size) -> fewer genes carried Most genes only carried on X chromosome - males > females to show x-linked characteristics for recessive alleles -> only need one copy E.g. colour blindness + haemophiliac = x-linked
Stem cells -> specialised cells
- stem cells -> specialised cells = differentiation
- stem cells = unspecialised
- divide by mitosis -> new cells -> specialised - ability of stem cells to differentiate = potency
- Totipotency
- Pluripotency - Found in:
- embryo
- intestines
- bone marrow
- plants = growth areas
note: adult stem cells = less flexible; less differentiation potency
Totipotency
Ability to produce all cell types (all specialist cells & extraembryonic cells)
Pluripotency
Ability to produce all specialised cells
- lose extraembryonic ability after first few cell divisions in the embryo
Gene expression & differentiation
Stem cell = same genes - expressed only if active mRNA only transcribed from active gene -> translated -> protein Proteins modify cells: - determine cell structure - control cell processes (inc gene activation) Changes to cell via proteins cause differentiation - difficult to reverse - stays specialised
Transcription Factors:
= proteins that bind to DNA
= activate/deactivate genes (expression) by increasing/decreasing transcription rate
Activatiors = increasing factors (help RNA polymerase bind to DNA) Repressors = decreasing factors (prevent RNA polymerase bind to DNA)
Gene expression & differentiation: Red blood cell exp
Red blood cells:
- lots of haemoglobin
- no nucleus
- produced from bone marrow stem cells (type)
- stem cell :
- > cell with gene for haemoglobin production activated
- > nucleus removal gene activated also
- > red blood cell
Transcription Factors: Prokaryotes
Prokaryotes -> TF’s binds to Operons
- OPERON = dna section that contains a cluster of structural genes that are transcribed together alongside control element + (usually) regulatory gene
– structural gene = useful protein e.g. enzymes (code for)
– control elements = promoter (DNA sequence before structural gene that RNA polymerase binds to)
= Operator( DNA sequence TF binds to)
– regulatory gene = codes for activator or suppressors
Transcription Factors: Eukaryotes
Eurkaryotes -> TF bind to specific DNA sites
-> near start of target genes ( genes they control expression of)
Transcription Factors: E.coli -> Lac operon
- E.coli = bacterium -> respires glucose, or lactose if glucose unavailable
- genes to respire lactose (e.g. produce enzymes) -> lac operon
- Lac operon = 3 x structural genes (LacZ, LacY, LacA)
- produce proteins to help digest lactose
- > Beta-galactosidase
- > lactose permease
Transcription Factors: E.coli -> Lac operon
Lactose not present
Regulatory gene (lacL) produced Lac repressor (TF)
- > binds to operator site
- > blocks transcription (RNA polymerase cannot bind to promoter)
Transcription Factors: E.coli -> Lac operon
Lactose present
Lactose binds to repressor
-> changes repressor shape -> no longer can bind to operator
RNA polymerase begins structural gene for transcription
Treating disease with stem cells
- stem cell -> specilaised cells; replace damaged tissues
- stem cell therapies:
- leukemia (kills bone marrow stem cells) -> bone marrow transplants - researching:
- spinal cord injuries -> nerve tissues
- heart disease + heart attack damage -> damaged heart tissue - benefits:
- many people die waiting for organ transplants -> stem cells could grow organs
- improve quality of life e.g. the blind
Adult Stem Cells
Adult body tissues (bone marrow) Relatively simple operation: - low risk - lot of discomfort Donor anesthetised Needle inserted into bone center (Hip) Small bone marrow quantity removed Adult stem cells aren't as flexible -> develop into limited range Own cells can be used -> less risk of rejection
Embryonic Stem Cells
Early embryos IVF (labatory) 4 to 5 days old - stem cells removed - rest of embryo destroyed Can develop into all cell types
Embryonic Stem Cells: Ehtical Issues
Destruction of viable embryo
Many believe fertilisation = genetically unique individual
- right to life
Fewer objections = unfertilised egg cells -> artificially divided
- could not last past a few days anyhow
Society has to consider arguments before use
Regulatory Authorities process
- Research proposals -> deciding if allowed
- ethical issues (research carried out for a good reason)
- no research uneccessarily repeated - licensing + monitoring centres involved in research
- trained staff -> understand implications
- no resource waste
- no unregulated work - guidelines + codes of practice
- work in similar manner (comparision)
- acceptable source of stem cells (e.g. maximum age of embryos + extraction method) - monitoring developments
- up to date guidelines
- changes in field regulate appropriately - info + advice -> Government + professionals
- promote science involved
- helps society understand
Phenotype variation: Continious
Individuals within population vary within a range - no distinct categories E.g.: - height -mass -skin colour
Phenotype variation: Discontinuous
Two+ distinct categories
E.g.:
- blood groups
Variation in Genotype
-> variation in phenotype
- Controlled by one gene = monogenic
- usually discontinuous - No. of genes at different loci = polygenic
- continious
Environmental Influence
- Height = polygenic
- nutrition - Monoamine Oxidase A (MAOA) = enzyme
- breaks down monoamines
- low levels -> mental health issues
= monogenic
- reduced by smoking + antidepressants - Cancer = genetic
- diet
- location - Animal hair colour = polygenic
- decreasing temperature triggers change
Environmental change -> Changes in gene expression
Eukaryotes: epigenetic control determines gene expression -> alters phenotype
- does not alter base sequence if DNA
- attaches/removes chemical groups to/from DNA
- > alters how easy it is for enzymes + proteins needed for transcription to interact with transcribed genes
Epiginetic changes play a role in normal cellular processes
Also occur in response to environmental changes e.g. lack of food, pollution
Increased methylation of DNA
-> represses a gene = epiginetic control
Methylation of DNA = attachment of methyl group to DNA coding for a gene
- always attaches at CpG site ( = cytosine + guanine next to one another)
- increased methylation -> changed DNA structure
- > proteins + enzymes (transcription) cannot bind to gene -> repressed
Histones
= proteins that DNA wraps around -> chromatin; makes up chromosomes
Chromatin can be highly or less condensed -> affects DNA accessibility (+ binding sites)
Histone modification (Epiginetic)
- Histone = Acetylated
- chromatin = less condensed
- > proteins (transcription) can bind - Acetyl groups removed
- chromatin = highly condensed
- no transcription -> genes repressed
How can epiginetic changes be passed on after cell devision?
Methyl groups usually removed during gamete production
- some escape & end up in gametes
- carry on epigenetic changes (repression/activation)
- equipped to deal with changed environment
