Lecture 2 Cells, DNA, mol Flashcards
the cell is
the basic organizational structure of human body
how many cells in body
50 - 100 trillion
differentiation is:
when cells specialize
cells vary in :
size
shape
function
what is a composite cell and its 4 major parts
a typical cell
- nucleus
- cytoplasm
- cell membrane
- organelles
what is function of cell/plasma membrane
- actively participates in cell metabolism
- barrier btw in & out of cell
what is structure of cell membrane
- dbl layer of phospholipids interconnected with other lipids (ex. cholestrol = helps stabilize membrane by reducing phospholipid mobility)
- proteins in membrane can be trans-membrane= integral/integrated or peripheral (on surface)
what is electrochemical gradient
- ELECTRO = charge -/+ inside vs outside of cell, dictates where ions want to go
- CHEMICAL = concentration inside vs outside of cell dictates where mol wants to go
- this is when those two forces move molecules across membrane
proteins in cell membrane function as these 4 things
- transporter
- receptors - signals
- cytoskeleton anchors
- enzyme activity
what is cytoplasm
thick solution that fills cell inside plasma membrane
- Cytosol = water
- organelles = solids
what is mitochondria
powerhouse of cell
-generates ATP for cell to use as energy
what is endoplasm reticulum
- area of protein synthesis
- lipid synthesis
- calcium storage and release
- smooth or rough ER
- rough ER has ribosomes on outer layer to create proteins
what are ribosomes
- made of RNA (make proteins then send to rough ER)
- site of protein synthesis
- on outside of rough ER
- uses mRNA to determine order of amino acids to create given protein
what is golgi apparatus
- process and package proteins and lipids in vesicles
- vesicles usually go to reach cell membrane and help expulsion of the proteins/ lipids outside the cell (preps proteins & lipids to send out of cell
what are centrioles
- tube like things near center of cell
- assist in cell division
what are microtubules
- major component cytoskeleton
- cellular mobility, intracellular transport, maintaing cell shape and structure.
What are microfilaments
- major component of the cytoskeleton
- coordinate contraction and transport of vesicles
What are cilia
Short hair like projections
- propel substances on cell surface
What are flagellum
- long tail like projections
- provide motility to sperm
What are Microvili
- tiny protrusions of the cell membrane
- increase absorption
Ex. Intestine
What is cell nucleus
Control center of the cell
What is nuclear envelope
- porous double membrane
- separates nucleoplasm from cytoplasm
What is nucleolus
- dense collection of RNA and proteins
- site of ribosome production
What is chromatin
- fibers of DNA and proteins
- stores info for synthesis of proteins
What is passive cellular transport and 4 types
Requires no energy
- simple diffusion
- facilitated diffusion
- osmosis
- filtration
What is active cellular transport and 4 types
Requires cellular energy
- active transport
- endocytosis
- exocytosis
- transcytosis
What is simple diffusion
- movement of substances from regions of higher concentration to regions of lower concentration.
- oxygen, carbon dioxide and lipid-soluble substances
What is facilitate diffusion
- diffusion across a membrane with the help of a channel or carrier molecule
- ex. Glucose and amino acids
What is osmosis
- movement of water through selectively permeable membrane from region higher concentration to region of lower concentration.
- water movement toward a higher concentration of solutes.
What is osmotic pressure
Ability of osmosis to generate enough pressure to move a volume of water
- increases as the concentration of non permeable solutes increases.
What is isotonic solution
Cells retain their normal size and shape as same solution/water concentration inside and outside of cell.
What is a hypertonic solution
Higher osmotic pressure (water loss)
What is Hypotonic solution
Lower osmotic pressure ( water gain)
What is filtration
- smaller molecules are forced through porus membrane
- hydrostatic pressure is important in the body
- molecules leaving blood capillaries
What is active transport
- carrier molecules transport substances across a membrane from regions of lower concentration to regions of higher concentration utilizing ATP (energy) to do so
- ex. Sugars, amino acids, sodium ions, potassium ions, etc..
What is sodium-potassium pump
Creates balance by pumping 3 sodium (Na+) out and 2 potassium (K+ ) into the cell.
-3:2 ratio
What is secondary active transport
- uses the energy stored in a concentration gradient
- the gradient is established through active transport.
- symporters move substances in the same direction
- antiorters move substances in opposite directions
What is endocytosis
- cele engulfs a substance by forming a vesicle around the substance
- net movement is into the cell
What are the 3 types of endocytosis
- Phagocytosis: substance is a solid. Produce phagosome (endocytotic vesicle) which combines with a lysosome
- pinocytosis: substance is mostly water. Produce vesicle
- Receptor-mediated endocytosis: requires the substance to bind to a membrane-bound receptor.
What is exocytosis
- Reverse of endocytosis
- substances in a vesicle fuse with cell membrane
- contents released outside the cell
- ex. Release of neurotransmitters from nerve cells
What is transcytosis
- endocytosis followed by exocytosis
- transports a substance rapidly through a cell
- HIV crossing a cell layer
What is DNA
Deoxyribonucleic acid
- double helix or 2 complementary strands
- Guanine, cytosine, adenine, thymine
What is RNA
Ribonucleic acid
- simple strand
- guanine, cytosine, adenine, uracil
Who were the first to publish a model of DNA structure
In 50’s Watson & Crick
A nucleotide is made up of:
1 phosphate group 1 sugar (deoxyribose=DNA, ribose=RNA) 1 nucleobase (=nitrogen base)
What are the obligatory base pairs of DNA
Adenine and thymine
Cytosine and guanine
What are the 2 processes of protein synthesis
- Transcrption: copying of the DNA code to a RNA strand
- Translation: taking the RNA code and reading it to transfer the information into a protein.
DNA -> RNA -> protein
What happens in transcription
- many enzymes are involves
- the 4 nucleotides dont differ structure, it’s their sequence that makes them unique
- the enzyme DNA polymerase causes the helix to unwind
- Nucleobases of RNA bind to the exposed DNA nucleotides to form mRNA
- mRNA that has undergone transcription is then modified in the nucleus by removing certain segment (INTRONS= non info regions) and then the remaining segments (EXONS= coding regions) are joined (spliced)
- lastly mRNA exits the nucleus and goes into the cytoplasm where the TRANSLATION will occur by the ribosomes to obtain protein
What else does DNA code for in transcription
- rRNA: joins with the ribosomal proteins to give rise to the ribosomes
- tRNA: searches and adds the appropriate codons to mRNA
- one codon (3 RNA base pairs) coded for a single amino acid
What happens in Translation
- mRNA joins 2 ribosome subunits and becomes sandwiched btw them
- protein synthesis begins at the codon AUG on the mRNA
- A tRNA with the matching anti-codon and amino acid will enter the A site of the ribosome
- tRNA will form h-bonds with mRNA
- at site P the peptide bonds are formed btw the amino acids
- at site E the tRNA is released without the amino acid
- this continues until the Stop Codon (UGA, UAA, UAG)
- the polypeptide chain detaches & if there is not another mRNA, the 2 subunits of the ribosome seperate.
- many ribosomes line up to translate the same mRNA in multiple copies of the same protein
Where do the newly created proteins go once produced by ribosomes
Into the cytoplasm
- all cells of an organism contain the same genetic package , but not all Gene’s are expressed in all cells
- each type of cell produces proteins necessary for it’s own functions and locations in the organism
What are two types of proteins that are created by ribosomes but then sent directly out of cell and only activates when it get to specific site
- Trypsin: pancreatic enzyme that’s secreted as trypsinogen in small intestine
- Enteropeptidase: (enterokinase) enzyme present in small intestine that activate the trypsinogen to trypsin
- tripsin digests proteins (dont want it to function until in small intestine)
What is an overview of basic cell cycle 4 phases
G1 - Growth 1 (cells that do not reproduce stop here)
S - growth and DNA synthesis
G2 - growth and final preparation for division
- those 3 fall under Interphase
M - Mitotic phase
What are the 2 types of cell division
Somatic (mitosis) = diploid (2n) = 46 (23 pairs) chromosomes -> to repair and replace
Reproductive (meiosis) = haploid (n)= 23 chromosomes -> reproduction
What is Interphase
- where cell spends most time doing norm function
- at start chromosomes are not condensed but form filamentous mass of chromatin
- chromosomes will condense only for cell division; in this state it is formed of 2 chromatids which are 2 copies of the same chromosome
- chromatids are from DNA replication
- when chromatin duplicates, each chromatids remain attached to its copy by the Centromere
- if the cell will divide, DNA & the centrosomes will be be replicated in this phase
- protein & RNA synthesis necessary for cell division is undertaken
- there are 3 sub steps of interphase
What happens in G1 phase
- cell is occupied with its metabolic function and it’s own upkeep
- cells that do not divinde (ex. Nervous & myocytes) remained blocked at G1 (called G0)
- few cell activities are related to cell division here except near the end where centrioles replication occur
- the length of time varies a lot (few minutes to a few days)
What happens in S phase
- here DNA is replicated
- chromosomes replicate & are attached by their centromere & remain at this point in the form of chromatin
- DNA replication cannot be cancelled at this point
- each of the 2 DNA strands is read & a complementary copy is done; DNA-POLYMERASE is involved
What happens during G2 phase
- brief phase of growth
- final prep for cell division (synthesis of certain necessary proteins & RNA)
- this is very important bcs once prophase has begun (chromosomes condensed), mRNA synthesis is no longer possible.
What are the 2 types of cell division
- Nuclear division:
- mitosis (somatic)
- meiosis (gametes) - Cytoplasmic division:
- cytokinesis
What is end result of mitosis
1 mother cell divides into 2 identical daughter cells
what are the 4 steps after interphase of mitosis
- Prophase
- Metaphase
- Anaphase
- Telophase
Describe prophase of mitosis
- Chromatin condenses into chromosomes
- pair of chromatids are held by their Centromeres
- nucleolus & nuclear envelope disappear
- Centrioles: 1. migrate to opposite poles, 2. organize the mitotic spindle (microtubules)
What are the 3 microtubules
- Polar: go beyond chromosomes & go towards opposite poles
- Kinetochore: these microtub. attach to the kinetochores (these attach to chromosomes)
- Aster: go in opposite direction of the mitotic spindle (anchors spindle to plasma membrane)
What happens in metaphase of mitosis
Chromosomes align at the Equatorial plate
What happens in Anaphase of mitosis
- Centromere divide & each chromosome separate from its homologue
- chromosomes migrate twrd the poles by shortening the kinetochore microtubules
- chromosomes migrate in the form of a V & crosses all the cytoplasm
What happens in Telophase of mitosis
- chromosomes return to the state of chromatid
- kinetochore microtubules disappear & polar microtubules elongate
- mitotic spindle dissolves
- nuclear envelope form again
- 2 cells are almost divided
What is cytokinesis
-the cells divide its cytoplasmic content in & becomes 2 cells
What is meiosis
- the cells divide to give 4 half cells
- only done at the level of the ovaries & the testis to form gametes
- interphase is the same as mitosis
What happens in prophase 1 meiosis
Same plus synapsis occurs: homologous chromosomes come tgthr along their length to form tetrads
-during synapsis the arms of homologous chromatids wrap around each other = crossover (trading segments)
What happens in metaphase 1 meiosis
the tetrads align randomly on the spindle equator in prep for anaphase
What happens in anaphase 1 meiosis
- centromeres DO NOT separate, so the sister chromatids (dyads) remain firmly attached.
- the homologous chromosomes do separate from each other & the dyads move twrd opposite poles of the cell
What happens in telophase 1 meiosis
- nuclear membranes re-form around the chromosomal masses
- spindle breaks down
- chromatin reappears as telophase & cytokinesis end
- the 2 daughter cells (now haploid) enter a second interphase-like period, called interkinesis before meiosis ii occurs (no 2nd replication of DNA)
What happens in Meiosis II
- Starts with product of meiosis I (2 haploid daughter cells)
- undergoes mitosis-like nuclear division
- end result is 4 haploid cells each diff than mother
