Mitosis, Meiosis, & Cell Division

• These revision slides contain some key topics to study regarding human cells.

Mitosis

• Mitosis is cell division that results in two identical cells
• Some somatic cells divide via mitosis for growth and tissue repair
• Human somatic cells contain 46 chromosomes, or 2 sets of 23, and are diploid
• The nucleus divides into two new nuclei, each receiving the full set of 46 chromosomes through mitosis
• Cells produced via mitosis have two sets of chromosomes
• Mitosis is a nuclear division process immediately followed by cell division, where one cell divides into two genetically identical cells

Meiosis

• Meiosis is the production of gametes such as sperm and eggs
• During meiosis, a diploid germline cell divides to form gametes, or sex cells, to produce sperm and eggs
• Meiosis enables the production of haploid sperm and eggs
• Division of germline cells result in four nuclei being produced during meiosis
• Each new nucleus receives a single set of 23 chromosomes and becomes a gamete which is haploid. This is meiosis

Cancer

• Cell division is typically controlled by the cell cycle through chemical signals to regulate cell growth rate and division
• Cancer cells do not respond to regulatory signals, resulting in rapid and uncontrolled cell division
• Tumors are a mass of abnormal cells that do not respond to cell signals causing them to divide too quickly
• Benign tumors refer to a discrete group of abnormal cells that may not cause problems and can be removed
• Malignant tumors are cells that lose surface molecules responsible for attachment to the original tumor, leading to the spread of new, secondary tumors, like malignant melanoma and some breast cancers

DNA Nucleotides

• A DNA nucleotide contains three parts: a phosphate, a deoxyribose sugar, and one of the nitrogenous bases
• The four bases are: adenine, thymine, cytosine, guanine
• The phosphate is represented by a circle, and the deoxyribose sugars are represented by a pentagon
• It's important to be able to sketch out a nucleotide

DNA Structure

• The components of DNA structure are bases, sugars(called deoxyribose sugar), and phosphates
• The bonds between bases are hydrogen bonds, which are weak bonds
• A bonds with T, and C bonds with G in the complementary base pairing rule

RNA Structure

• RNA nucleotides contain a phosphate group, ribose sugar, and one of four bases which are: A, U, C, G

RNA Compared to DNA

• RNA contains the bases A, C, G, and U whereas DNA contains the bases A, C, G, and T
• RNA contains ribose as a sugar where DNA contains deoxyribose
• RNA is usually single-stranded and DNA is usually double-stranded

Types of RNA

• mRNA carries a copy of DNA code from the nucleus to the ribosome, and is a linear molecule with codons
• Each tRNA molecules carries its specific amino acid to the ribosome, and is cloverleaf-shaped molecule with anti-codons
• rRNA is a component of the ribosome itself along with proteins

mRNA

• mRNA is a liner, unfolded single strand of RNA that has codons, or a triplet of bases
• mRNA is produced during transcription by copying the code on the appropriate gene on the DNA chromosome
• Before leaving the nucleus, mRNA is spliced and moves to the ribosome to direct translation

Splicing

• Regions of a gene that code for protein are exons, which are expressing or coding regions
• Regions of a gene that are non-coding are known as introns, which are intervening regions that don't code for protein
• The type of modification to mRNA to remove introns from the primary transcript is called splicing

tRNA

• tRNA carries amino acids to the ribosome for polypeptide chain forming
• tRNA has an anticodon, or exposed triplet of bases, and has an attachment site for the amino acid

Translation

• Each triplet of bases, or codon, on the mRNA is complementary to the anticodon on the corresponding tRNA
• There is no T in RNA, or thymine - it is replaced by U (uracil) in complementary pairing: A-U and C-G
• Peptide bonds are formed between amino acids to form a polypeptide chain

Single Gene Mutation

• Single gene mutations are caused by a change to nucleotide sequences, and can occur in three ways: nucleotide substitution, insertion, or deletion
• A missense substitution mutation leads to swapping one amino acid for another
• A nonsense single gene mutation is where a stop codon is reached prematurely
• When a mutation causes a stop codon to be reached too early, the polypeptide chain formed ends up shortened and does not function, and it is called a nonsense mutation
• Splice site mutations are where some introns are retained or some exons are not retained in the mature transcript

Chromosomal mutations

• Chromosome structure mutations cause substantial changes to the chromosome
• Deletion mutation is where part of one chromosome is removed
• Duplication mutation is where a section of a chromosome is added from its homologous partner
• Translocation mutation is where a deleted part from one chromosome attaches itself to a non-homologous chromosome
• Inversion is when a section of a chromosome is reversed

Human genomics

• Genomics is the study of the human genome
• The genome of an organism is the entire hereditary information encoded in DNA
• The genome consists of genes and other DNA sequences that do not code for proteins
• Genomics has the potential to allow a more personalised approach to medicine and prescribing drugs, with the use of bioinformatics and pharmacogenetics

Bioinformatics

• Bioinformatics uses computer technology, molecular biology, and statistical analysis
• Genomic sequencing produces huge amounts of data which gets analysed by computers
• Bioinformatics allows identification and analyses of the sequence of a person's DNA
• Genomics has had great advances in recent years with the help of bioinformatics through acquiring genomic sequences faster

Pharmacogenetics

• Pharmacogenetics is the study of effects of pharmaceutical drugs on members of human population via genomic information
• The population is genetically diverse meaning the effects of drugs can be therapeutic, neutral, or adverse
• So pharmacogenetics allows doctor's to decide which medicines to prescribe via genomic information for personalized medicine.

PCR

• PCR, polymerase chain reaction, is the amplification of a DNA fragment
• Amplification is how many copies from a strand of DNA are made
• Temperature in cycles of PCR: -92-98°c to melt DNA by breaking hydrogen bonds -50-65°c to allow primers to anneal or bind to regions on DNA strands -70-80°c allows Taq polymerase to work on building the new strand
• The quantity of DNA doubles after each cycle
• Heat tolerant DNA polymerase is used in the 3rd stage to add new nucleotides and create a new strand
• In the 5'-3' direction, strands extent to add new nucleotides at the 3' end

Metabolic Pathways

• Catabolic pathways break down complex molecules to simpler ones and releases energy
• Anabolic pathways build up more complex molecules and uses up energy
• If a metabolic pathway releases evergy it's catabolic, but if it requires energy it is anabolic

Regulation of metabolic pathway

• Products of a pathway can build up to levels that inhibit earlier stage which causes the pathway to halt until levels reduce
• Increased levels of ATP and citrate regulate Glycolysis
• High levels of ATP inhibit phosphofructokinase so subsequent stages of pathway would not work

Inhibitors

• Inhibitors decrease the rate of enzyme-controlled reactions
• Competitive inhibitors compete with substrates for the active site and prevent the substrates from binding
• Non-competitive inhibitors bind to an area other than the active site like the allosteric site, to alter the enzyme shape so substrate can longer bind to the active site

Aerobic Respiration

• Stage 1: Glycolysis, occurs in the cytoplasm of the cell
• Stage 2: Citric Acid Cycle, occurs in Mitichondrion Matrix and requires oxygen
• Stage 3: The Electron chain occurs on cristae of mitochondrion and requires oxygen
• In Stage 1, glycolysis converts glucose to pyruvate, resulting in a net gain of 2 ATPS.
• Stage 2 is citrate formed by acetyl combining with oxaloacetate is converted to intermediate products to allow for removal of carbon and hydrogen.
• Carbon forms carbon dioxide and hydrogen is removed from dehydrogenase enzymes.
• The coenzyme NAD becomes NADPH, which then transports hydrogen ions and electrons to the Electron Transport Chain

Electron Transport Chain

• The process of Stage 3 occurs on the cristae of the mitochondria
• The ETC is group of proteins that contains the ATP synthase, embedded in the inner mitochondrial membrane including ATP synthase enzyme
• Hydrogen ios are pumped membrane, then flow back across the membrane via ATP synthase which bonds to Pi to produce ATP
• Hydrogen combines with electrons and oxygen to form water
• ETC products are ATP and water

Energy Systems in Muscle Cell

• The table highlights many differences involving both the fast twitch and slow twitch muscle fiber systems

Command Words

• These command words are in the question, paying attention to what you being asked to do
• Compare means discussing both sets of data to find the difference
• Name means just the name needed
• Describe means need an information sentence or if marks are available have 2 pieces of informative sentences

To Calculate Percentage Increase

• Use the formula: percentage increase = to calculate the percentage increase
• If something from 30 units goes up to 40 units, that means the actual increase is 10, the starting value is 30 so percentage increase is 10/10x100 = 33.3%

Graphs

• Level 6 can be tricky, highlight with 2 color pens and appropriate colors to highlight the data lines. The two Y axes will have different sales so take note of the information each represents
• Be precise for the graph reading portion

Test your knowledge of cell division processes including mitosis and meiosis. This quiz covers chromosome numbers, tumor characteristics, and the basics of DNA. Perfect for biology students!