Topic 3.1 Flashcards
Organisms
All living organisms are made up of cells and share some common features
Eg:
- Prokaryotes are made up of prokaryotic cells
- Eukaryotes are made up of eukaryotic cells
-> both types contain organelles, which have specific functions
Protein production and transport in cells
Proteins can be made at different ribosomes
. Free ribosomes in the cytoplasm make proteins that stay in the cytoplasm
. Ribosomes on the RER (rough endoplasmic reticulum) make proteins that are excreted or attatched to the cell membrane -> these proteins are folded and processed (adding additional groups + forming secondary, tertiary and quaternary structures) by the RER and the transported in vesicles to the Golgi apparatus where proteins may undergo further processing before entering more vesicles to be transported around the cell
Eg. Extracellular enzymes move to the cell surface and are excreted
Nucleus: description
- Large
- Double membrane with pores (nuclear envelope)
- Chromatin (made from DNA and histone proteins, DNA is wrapped around histone proteins)
- nucleolus
Nucleus: function
. Stores genetic information (DNA)
. Controls cell activity of cell by controlling transcription of genes and translation of these into proteins
Lysosome: description
. Membrane bound
. Little internal structure
Lysosome: function
- Contains digestive enzymes which destroy:
. Invading cells
. Worn out parts
Ribosome: description
. Very small
. Not membrane bound
. Made up of proteins and RNA
. They can be: free floating in cytoplasm + attached to RER
Ribosomes: function
Site of protein synthesis (translation)
Rough endoplasmic reticulum (RER): description
. Fluid filled
. Membrane bound sacs
. Ribosomes attached to surface
Rough endoplasmic reticulum (RER): function
. Fold and processes (folding, adding additional groups) proteins that have been made at ribosomes + packages proteins (sent to Golgi)
Smooth endoplasmic reticulum (SER): description
. Fluid filled
. Membrane bound sacs
Smooth endoplasmic reticulum (SER): function
Synthesises (synthesised from fatty acids and glycerol) and processes lipids + packages (sent to Golgi)
Golgi apparatus: description
. Fluid filled
. Membrane bound sacs
. Often have vesicles at the edges of the sacs
Golgi apparatus: function
. Processes and packages proteins and lipids into vesicles for exocytosis
. Makes lysosomes
Mitochondrion: description
. Oval shape
. Double membrane (inner membrane folded to form cristae)
. Inside is the liquid called the matrix -> which contains ATP involved in respiration
Mitochondrion: function
. Site of aerobic respiration
. Where ATP is produced
Centriole: description
. Very small
. Made up of hollow microtubules (tiny protein cylinders)
. Found in animal cells + some plant cells
Centriole: function
Involved in separation of chromosomes during cell division
Prokaryotic cells: cytoplasm
. No membrane-bound organelles
. Ribosomes smaller than those in eukaryotes
Prokaryotic cells: cell wall
. Supporting the cell preventing it from changing shape
. Made up of glycoprotein called murein
Prokaryotic cells: Pili
. Help prokaryotic cells to stick together and can be used to transfer genetic material between cells
. Short hair like structures
Prokaryotic cells: capsule
. Made up from secreted slime produced by bacteria that protect bacteria from immune cells
. Used for protection
(some prokaryotic cells have them and some don’t)
Prokaryotic cells: mesosomes
Inward folds in the plasma mebrane
Prokaryotic cells: plasmids
. Small loops of DNA
. Can be passed between cells
Prokaryotic cells: circular DNA
. Long-coiled up strand
Prokaryotic cells: flagellum
. Long tail like structure that rotates to make prokaryotic cell move (some prokaryotic cells have them and some don’t)
Tissues
Group of similar cells that are specifically adapted to work together to carry out a particular function
Eg.
- Epithelial cells group together to form epithelial tissue
- Muscle cells group together to form muscle tissue
Organs
Group of different tissues that work together to perform a particular function
Eg.
- Tissues including cardiac muscle tissue, blood vessel tissues and connective tissues group together to form the heart
- Tissues including palisade mesophyll, spongy mesophyll and vascular tissue group together to form leaves
Organ system
Group of different organs that work together to perform a particular function
Eg.
- Respiratory system made up of all the organs, tissues and cells involved in breathing i.e lungs, trachea, nose, mouth, larynx and diaphragm
Cell cycle
Period of cell growth and DNA replication called interphase followed by mitosis
Cell cycle: interphase
During interphase the cell carries out normal functions whilst it prepares to divide:
. Cell’s DNA is unravelled and replicated to double its genetic content
. Organelles are replicated so it has spare ones
. ATP content is increased to provide energy for cell division
Cell cycle: interphase growth stages
. Gap phase 1: cell grows and new organelles and proteins are made
. Synthesis: cell replicated DNA ready to divide by mitosis - cell prepares to divide but it also continues to carry out normal processes
. Gap phase 2: cells keep growing and proteins needed for cell division are made
Mitosis
Parent cell divides to produce two genetically identical daughter cells
-> mitosis is needed for growth of multicellular organisms, for repairing damaged tissues and for asexual reproduction
-> when DNA divides during mitosis, chromosomes double to form two identical arms, each called chromatid and collectively called sister chromatids - held together by a centromere
Division stages of mitosis (PMAT): prophase
. Chromosomes shorten + condense
. Nuclear envelope breaks down
. Centrioles move to opposite ends of cell and form spindle fibres (threads of protein that form a kind of web over cell)
Division stages of mitosis (PMAT): metaphase
. Spindle fibres form between the two centrioles
. Chromatids line up at the equator attached to spindle fibres to which centromeres are attached to
Division stages of mitosis (PMAT): anaphase
. Spindle fibres contract and pull apart chromosomes of the centromere
. Sister chromatids are pulled toward opposite centrioles by spindle fibres
Division stages of mitosis (PMAT): telophase
. Chromosomes form as DNA uncoils and become long and thin again
. Nuclear envelope reforms around each set of chromosomes
. Cytoplasm divides by process called cytokinesis
Gametes
Gametes are female and male sex cells found in all organisms that produce sexually that join together during fertilisation to form a zygote which divides by mitosis to form and embryo
-> gametes have a haploid nucleus so they only contain one set of chromosomes (23 in total for humans)
Adaptations of egg cells
. Follicle cells -> form protective coating
. Zona pellucida -> protective glycoprotein layer that sperm have to penetrate
. Egg cells are much larger than sperm cells
. Contain huge stores of nutrients to nourish developing embryo
Adaptations of sperm cells
. Flagellum -> allows sperm cell to swim towards egg
. Acrosome -> contains digestive enzymes t break down the egg cell’s zona pellucida and enable sperm to penetrate egg
. Contains lots of mitochondria to provide energy for tail movement
Fertilisation: acrosome reaction
- Sperm makes contact with zona pellucida
- This causes acrosome to fuse with sperm cell membrane which releases its digestive enzymes
- Enzymes digest the zona pellucida and sperm can now reach egg cell membrane
Fertilisation: cortical reaction
- Sperm cell membrane fuses with egg cell membrane
- Egg cell releases contents of vesicles called cortical granules into the space between the cell membrane and zonal pellucida
- The contents react with the zona pellucida causing it to harden preventing polyspermy (more that one sperm entering the membrane)
Fertilisation: fusion of nuclei
- Only the sperm nucleus enters the egg (tail is discarded)
- Nucleus of sperm fuses with nucleus of egg cell -> this is fertilisation
Meiosis
Cell division that produces four genetically different types of haploid gametes
-> occurs in ovaries and testes only -> produces gametes for reproduction
-> meiosis ensures genetic variation n the production of gametes through crossing over and independent assortment
. Has TWO cell division stages
Meiosis process
- The DNA replicates so there are two identical copies of each chromosome - chromatids
- DNA condenses to form two sister chromatids
- Chromosomes arrange themselves into homologous pairs
- 1st division- homologous pairs are separated,halving chromosome number
5 .2nd division- pairs of sister chromatids separated - Four new daughter cells that are genetically different from each other are produced - these are the gametes
Homologous pair
A pair of chromosomes of same length + contain the same genes at the same loci
Diploid
Contains 2 copies of each autosomal (non-sex) chromosomes
Crossing over
- The process that takes place before the first division in meiosis
1. Homologous pairs of chromosomes pair up
2. Two of the chromatids in each homologous pair twist up around each other
3. RECOMBINATION: the twisted chromatids break off their original chromatid rejoining onto the other chromatid
4. Chromatids still contain the same genes but have a different combination of alleles
Independent assortment
Different combinations of chromosomes in different gametes due to random arrangement/orientation of each homologous pair during cell division
Linkage of genes
Locus: locations of a gene on a chromosome
. Genes with loci on the same chromosome are said to be linked to
-> the closer together the loci of two genes on a chromosome the more likely they are to be linked because crossing over is less likely to separate them, therefore they are likely to be inherited together
Sex linkage
A characteristic is sex-linked when the locus of the alleles that codes for it is on a sex chromosome
. Females: XX. Males: XY
. Y chromosome is smaller than X (because it has fewer genes) so most genes in sex chromosomes are only carried on the X chromosome (X-linked genes)
. Males are more likely than females to show recessive phenotypes for genes that are sex-linked
-> this is as males only have one X chromosome they often only have one allele for sex-linked genes and so they express the characteristic of this allele even if its recessive
. Genetic disorders caused by faulty alleles on sex chromosomes are known as sex-linked disorders
-> colour blindness and haemophilia are X-linked disorders because both these disorders are caused by faulty alleles carried on the X chromosome
