Cellmol Reviewer - Biology Past Paper PDF

MODULE 1 Differentiate Prokaryotes to Eukaryotes Prokaryotes 1. Pro- means before= Before the Kernel 2. No membrane bound organelles 3. 3 times less genetic material compared to smallest eukaryotic cell 4. DNA is in the form of singular circular molecules Eukaryotes 1. Eu- means true= T...

MODULE 1 Differentiate Prokaryotes to Eukaryotes Prokaryotes 1. Pro- means before= Before the Kernel 2. No membrane bound organelles 3. 3 times less genetic material compared to smallest eukaryotic cell 4. DNA is in the form of singular circular molecules Eukaryotes 1. Eu- means true= True Kernel 2. Have membrane bound organelles 3. Larger Genomes 4. DNA is contained in chromosomes Similarities: 1. Both are surrounded by plasma membrane 2. Both contain similar macromolecules **Parts of Cell** 1. Cell Wall - Contains cellulose, microfibrils, hemicellulose, pectin, lignin, and soluble protein. - These components are organized into three major layers: the primary cell wall, the middle lamella, and the secondary cell wall. - Primary component of bacterial cell wall is Peptidoglycan/ murein. Consist of alternating NAG and NAM 2. Plasma Membrane - Semi permeable barrier that defines the outer of cell - Allows nutrients to enter the cell and filters unwanted materials - Maintains the osmotic pressure of cell - Also functions to communicate with other cells 3. Nucleus - Contains the chromosome that holds the DNA - Contains 2 membranes: inner defines the nucleus, outer membrane is continuous with RER 4. Cytosol - Contains cytoskeleton which maintain cell shape and mobility - MAJOR SITE OG CELLULAR METABOLISM because it contains large number of enzymes 5. Endoplasmic Reticulum - Most extensive membrane system in eukaryotic cell - RER: Site for Protein Synthesis - SER: Site for Lipid Synthesis 6. Golgi bodies - TRAFFIC POLICE because they play a key role in sorting many of the cell protein - Enzymes in the Golgi vesicles react with and modify secretory proteins passing through the Golgi lumen 7. Secretory vesicles - Transport secretory proteins that have been modified in the in the Golgi vesicles - EXOCYTOSIS: The secretory vesicles seem to bud off the trans side of the Golgi complex and then quickly fuse with the plasma membrane to release their contents in to extracellular space - Can also fuse with other similar secretory vesicles to become a limited storage reservoir. 8. Small vesicles - COATED VESICLES: Surrounded by a protein composed of Fibrous protein clathrin - Determine which membranes to fuse with to deliver their contents 9. Lysosomes - Degrade membranes and organelles that have outlived their usefulness - Also degrade extracellular macromolecules 10. Vacuoles - Functions as storage for water, ions etc. - Protozoans possess vacuoles that function in osmotic pressure 11. Peroxisomes and Glyxisomes - Contain enzymes that degrade fatty acids and amino acids and produce H2O2 - Peroxisome has CATALASE that degrade H2O2 to produce water and oxygen 12. Mitochondria - Powerhouse of the cell - GLUCOSE is the principal source energy in non-photosynthetic cell - The complete aerobic produces CARBON, WATER and ATP - The initial degradation on the CYTOSOL - Terminal degradation those involving oxygen occur in mitochondria - MATRIX and INNER MEMBRANE, sites of enzymes that catayze the final degradation 13. Chroloplasts - Largest organelle of plant cell - STROMA surrounds the thylakoids and grana where CO2 takes place - Contains DNA 14. Cilia and Flagella - Whiplike structures that extend from the plasma membrane - CILIA beat backward and forward - FLAGELLA rotate in screwlike manner - Similar to microtubules that compose the mitotic spindle 15. Plasmid - Naturally seen in bacterial cell but some also in Eukaryotic cell - Used as tools to clone, transfer and manipulate genes - Found in eukaryotes sucj as yeast and fungi - DNA fragments or genes can be inserted to plasmid to create recombinant plasmid that can be introduced by bacterium by process called TRANSFORMATION 16. Sperm Cell - Stripped down cells tasked to deliver DNA to the egg - The head contains a condensed HAPLOID nucleus - Chromosomes of many sperm have dispensed with the histones of somatic cell and are instead with simple high positively charged proteins called PROTAMINES 17. Ovum - Some eggs can be activated without sperm, process is PARTHENOGENESIS - The cytoplasm of egg can reprogram a somatic cell nucleus so that the nucleus can direct the development of a new individual - Many eggs contain CORTICAL GRANULES in the cortex to prevent POLYSPERMY MODULE 2 Biomolecules 1. Proteins - Working molecules of the cell that catalyze an extraordinary range of chemical reactions, provide structural rigidity, control membrane permeability. - Made up of amino acids - PEPTIDES are polymers of amino acids 2. Nucleic Acids - Store genetic information - Directs gene expression by instructing proteins to synthesize and in what quantities 3. Lipids - A major structural protein component of biomembranes 4. Carbohydrates - Key source of energy (glucose) - Ribose and Deoxyribose are essential constituents of nucleic acids - Glycoproteins and Glycolipids are important constituents of cell membranes 1. Monosaccharides- One sugar molecule ie. Glucose, Fructose, Galactose 2. Disaccharides- two sugar molecules ie. Sucrose, lactose, maltose 3. Oligosaccharides- Two-ten sugar molecules ie. Raffinose, Stachyose 4. Polysaccharides- Ten or more sugar molecules ie. Starch, glycogen, cellulose 1. Sucrose: Glucose+ Fructose 2. Lactose: Galactose+ glucose 3. Maltose: Glucose+ Glucose Raffinose- Found in beans and certain vegetables Fructooligosaccharides: Plant derived oligosaccharides Galactooligosaccharides: Dairy derived oligosaccharides Starches in Plants 1. Amylose 2. Amylopectin Omega-n - Refers to the number of the carbon atom with the first double bond from the METHYL END 1. Omega-3: essential fats for heart, brain and metabolism. Most people don't consume this 2. Omega-6: Provide body with energy. Abundant in the diet 3. Omega-9: Non essential fats produced by body 1. Heart Disease 2. Pancreatitis 3. Type A Diabetes Classification of Amino Acids 1. Primary Structure - Linear arrangement of amino acids residues along a polypeptide chain 2. Secondary Structure - Folding of parts of the polypeptide chain into regular structures such as HELICES 3. Tertiary Structure - The folding of regions between alpha-helices and B pleated sheets as well as the combination of secondary features 4. Quartenary structures - Organization of polypeptide chains into single protein molecule Nucleic Acids - Consist of a Phosphate group, a 5-carbon sugar (Pentose) , and an organic base - Purines: Adenine, Guanine - Pyrimidines: Cytosine, Thymine, Uracil - Leading strand: 5'-3' - Lagging strand- 3'-5' RNA - Can act as an enzyme and genetic materials (eg. Virus) CHAPTER 3 Genome - Entire set of DNA instructions found in cell The Cell Cycle - Dividing cells go through the cell cycle that is marked by a set of events. 1. **G1 phase (gap 1)** is the time when genes are transcribed and translated. 2. **S phase** is when DNA replication occurs. 3. **G2 phase (gap 2)** is the interval during which the cell prepares for the M phase, mitosis. Mitosis- Somatic Cell Meiosis- Sex Cells Meiosis-Mitosis Process (PP everytime) (14113) 1. Prophase 1(early) (1) - Synapsis and crossing over occurs 2. Prophase 1( late) (4) - Chromosome condense and become visible. Nuclear envelope fragments. Spindle forms. Spindle fiber attaches to the chromosome 3. Metaphase 1 (1) - The chromose align along the equator of the cell 4. Anaphase 1 (1) - The chromosome goes to the opposite poles of the cell 5. Telophase 1 (3) - The nuclear envelope partially assemble around the chromosomes. Spindle disappears. Cytokinesis divides the cell into two. - Meiosis in females takes decades to happen while in male it takes a few days 1. The mature cell divides into two: one somatic cell and other one turns into primary spermatocyte through the process of mitosis 2. The primary spermatocyte will undergo meiosis to form 2 secondary spermatoctytes 3. The secondary spermatocyte will again undergo meiosis to form 2 secondary spermatids. 4. Spermatids will undergo differentiation to form tadpole shaped spermatozoa Oogenesis Process 1. The process starts with a diploid oogonium 2. The primary oocyte will undergo meiosis to form a small polar body and a large secondary oocyte. 3. The secondary oocyte will again undergo meiosis to form another polar body and now a mature ovum **Explain the processes of Cyclins** Entry into the cell cycle at the restriction point occurs in response to mitogenic stimuli (proteins that bind to cell surface receptors) that set off a cascade of events resulting in stimulation of transcription of Cyclin D. - **Cyclin D** accumulates and interacts with **cyclin-dependent kinases (Cdks) 4 and 6** in **G1 phase**. Checkpoints: 1. Cell size 2. Nutrients 3. DNA Damage - This leads to phosphorylation of the Rb protein, which releases transcription factors from inhibition, leading to synthesis of **Cyclins A and E,** which interact **with Cdk2** to initiate DNA synthesis or the **S phase**. Checkpoints: 1. DNA Damage 2. DNA Replication - Upon completion of the S phase, **mitotic phase cyclins (A and B)** accumulate and interact **with CDK1**, triggering **mitosis** or M phase. Checkpoints: 1. Cell size 2. DNA replication Complexes that highly regulate processes in Meiosis and Mitosis (4) 1. **Mitotic cyclin--Cdk complexes** are involved in directing the dissolution of the nuclear membrane, formation of the spindle, and alignment of chromosomes on the spindle. 2. The sister chromatids are held together at the centromere by the **cohesin protein complex**. 3. Chromosome separation is triggered by activity of the **anaphase protein complex (APC)**, which stimulates inactivation of mitotic cyclin and enzymatic cleavage of cohesion at the centromeres. 4. **Spindle microtubules** function as motors, propelling the sister chromatids (or chromosomes, in the case of meiosis) toward the spindle poles. - Several genetic disorders are associated with mutations in the genes that encode **cohesin proteins** **Uses of Protein Checkpoints such as ATM and ATR** - DNA damage stimulates the proteins **ATM (ataxia telangiectasia mutated) and ATR (ATM and Rad3-related)**, which leads to activation of the **transcription factor p53**. - **p53** stimulates transcription of **p21**, which binds to and inhibits **G1--S/Cdk and S--Cdk** complexes, preventing further DNA replication until damage is repaired. - ATM and ATR also **activate proteins that inhibit M cyclins**, preventing a cell with DNA damage from **entering mitosis**. - If the **DNA damage is too extensive** to repair, p53 initiates programmed cell death, called **apoptosis**. Module 4 Chromosomes - The human karyotype consists of 22 pairs of non-sex chromosomes (autosomes) and two sex chromosomes, XX for females and XY for males. - **Chromatin** is a double stranded helical structure of DNA - DNA is complexed with histones to form **nucleosomes** - **Each nucleosome consists of 8 histones proteins** around which the DNA wraps 1.65 times - **Chromatosome** consists of a nucleosome and H1 histone - Chromosomes are classified according to size and position of the centromere into a standard array referred to as the **karyotype.** **Karyotype** - The complete set of chromosomes of an individual; describes the chromosome number and structure **Karyogram** - is a written description of an organism's chromosomes and allows determination of its karyotype - In human chromosomes, names are **based on size (length)**, hence chromosome 1 is the largest chromosome - By convention, chromosomes are **arranged in a pattern according to size and appearance** **Different Types of Karyotypes/ centrome locations (4)** The centromere divides most chromosomes into a **long arm** (designed the **q arm**, or "q") and a **short arm** (designated the **p arm**, or "p"). 1. **Metacentric** - Centrome in the middle A diagram of a cell Description automatically generated 2. **Submetacentric** - Centromere between middle and end -  3. **Telocentric** - Centrome at the end A purple and blue balloon Description automatically generated 4. **Acroncentric** - Centromere at the end - Chromosmes are 13,14,15,21 and 22 - These regions often remain decondensed, forming stalks, with small knobs at the end referred to as **satellites**.  - The **centromeres** are surrounded by blocks of highly repeated DNA sequences. - A major component, **the alpha-satellite DNA** consists of thousands of copies of a 171bp repeat which remains highly compacted throughout the cell cycle. - The **telomeres** consist of 10--15 kb of a repeat unit GGGATT, with repeated sequences extending for 100--300 kb inside of this region. **SINE vs. LINE Sequences** - **SINE** sequences are **GC rich and tend** to be found in **gene-rich areas**, - whereas **LINEs** are **AT** rich and are found in **gene-poor regions**. - **Chromosome banding** reflects differences in protein binding and chromatin condensation, which **is greater in AT-rich, gene-poor regions** - **Fluorescence in situ hybridization (FISH)** permitted detection of deletions or duplications of about a million base pairs **Autosomes** - are chromosomes that are present in the same numbers in males and females **Gene TDF** - that is present only in Y chromosomes **encodes a protein** that **makes the gonad mature into a testis**; XX embryos do not have this gene and their gonads mature into ovaries by default **Why is Y chromosome called a genetic wasteland?** - Lacking a functional **SRY gene,** mammalian embryos develop as females. - Those definitions refer to the fact that the Y-chromosome, compared to other chromosomes, **has few genes**. **Changes in Chromosome Number** 1. **Aneuploidy** - is the addition or subtraction of a chromosome from a pair of homologs 1. **Monosomy** - The **absence of one member of a pair of homologous chromosomes** is called monosomy and is indicated by **2n-1** 2. **Trisomy** - **There are 3 rather than the normal 2 homologs** of a particular chromosome and the condition is indicated as **2n+1** 2. **Polyploidy** - is the condition in which entire chromosome sets are duplicated; appears to be beneficial in some organisms especially many species of food plants 3. **Monoploids** - in many species of hymenopterans (bees, wasps and ants) males are monoploid and develop from unfertilized eggs; these males do not undergo meiosis to produce gametes, instead sperm is produced after mitosis - Female bees are diploid and are formed when an egg is fertilized by a sperm - If an egg is not fertilized, it can still develop into a male drone - This form of sex determination produces more females -- worker bees, than male bees that are only needed for reproduction - **Haploid-diploid sex determination system** - **Stable polyploids** generally have even number of copies of each chromosome **(diploids 2n=2x, tetraploid 2n=4x, hexaploid 2n=6x and so on)** - Polyploids with an odd number of chromosomes e.g**. triploids (2n=3x)** tend to be **sterile** **Many crop plants are hexaploids or octoploids** - Polyploid plants tend to be larger and healthier than their diploid counterparts - The strawberries sold in supermarkets are octoploids (8x) strains and are much larger than those farmed using wild diploid strains - Bananas, watermelons and other seedless plants are triploid; triploid banana is propagated asexually from cuttings or tissue culture while seedless watermelon is produced sexually by crossing a tetraploid watermelon with a diploid watermelon - By crossing a haploid chromosome, this leads to sterile or seedless plants **Chromosome Abnormalities** Abnormalities that involve changes in a segment of a **single chromosome** 1. **Deletions** - The chromosome fragment breaks down 2. Duplications - The chromosome segments double  3. Inversion - Broken chromosome part joins it again but it is turned 180 degrees A diagram of a diagram of a diagram Description automatically generated with medium confidence Changes that involve **2 non-homologous chromosomes** 1. **Insertion** -- DNA from one chromosome is moved to a nonhomologous chromosome in a unidirectional manner 2. **Translocation** -- the transfer of chromosome segments is bidirectional and reciprocal (reciprocal translocation) - Chromosome breakage occurs infrequently as a result of physical damage (e.g. by ionizing radiation), movements of some types of transposons and other factors Module 5 Central Dogma DNA-DNA: DNA Polymerase - DNA Replication DNA-RNA: RNA Polymerase - Transcription RNA-Protein: Ribosome - Translation **DNA Replication** - Process in which the cell makes an identical copy of itself - The first step is to "unzip" the double helical structure of DNA catalyzed by the enzyme **helicase** which breaks the hydrogen bonds holding the complimentary bases of DNA - The unwinding of the 2 single strands of DNA results in a **replication fork** 1. **3' to 5' direction** - **Leading Strand** - (towards the replication fork) - Continuous - Template Strand - Antisense strand 2. **5' to 3' direction** - **Lagging strand** - (away from the replication fork) - Discontinuous - Coding strand - Sense Strand  **In the leading strand:** - A **primer binds** to the end of the leading strand and acts as the starting point for DNA synthesis - **DNA polymerase** binds to the leading strand and "walks" along the strand adding new complimentary nucleotide bases to the strand of the DNA in a 5' to 3' direction; - **replication is continuous** **Lagging strand** - Numerous **primers** bind at various points along the lagging strand - these act as starting points for the addition of complimentary bases in the 5' to 3' direction producing fragments called **Okazaki fragments** - replication in the lagging strand is **discontinuous** - Once all the complimentary bases are in place, an enzyme called **exonuclease** will catalyze the removal of the primer sequences - The gaps are then filled with complimentary bases - The enzyme **ligase** joins the fragments to make 2 continuous double stranded DNA - The product of DNA replication are 2 DNA molecules consisting of one new and one old chain of nucleotides, hence semiconservative - Following replication, the new DNA winds up into a double helix **Transcription** - is the process by which the information in a strand of DNA is copied into a new molecule of messenger RNA (mRNA). - Transcription is carried out by an enzyme called **RNA polymerase** and a number of accessory proteins called **transcription factors**. - **Bacteria and archaea have only one RNA polymerase**. - Eukaryotes have at least three classes of polymerases 1. (Pol). **Pol I synthesizes the large ribosomal RNA (rRNA) precursor.** 2. **Pol II transcribes all the messenger RNAs** (mRNAs). 3. **Pol III catalyzes the synthesis of small untranslated RNAs such as the transfer RNAs (tRNAs) and the 5S rRNA.** - Although the mRNA contains the same information, it is **not an identical copy of the DNA segment**, because its sequence is **complementary to the DNA template**. - the RNA molecules produced by transcription are released from the DNA template as **single strands**. - **Transcription factors (TF**) can bind to specific DNA sequences called **enhancer and promoter sequences** in order to recruit RNA polymerase to an appropriate transcription site. - Together, the TF and RNA polymerase form a complex called the **transcription initiation complex**. - This complex initiates transcription, and the **RNA polymerase** begins mRNA synthesis by matching complementary bases to the original DNA strand. - The mRNA molecule is elongated and, once the strand is completely synthesized, transcription is terminated. The newly formed mRNA copies of the gene then serve as blueprints for protein synthesis during the process of translation. Steps in RNA Transcription 1. **Pre-initiation** - Transcription is catalyzed by the enzyme **RNA polymerase.** RNA polymerase and cofactors bind to DNA causing it to unwind and creating an initiation bubble. This creates a space for RNA polymerase to access a single strand of DNA. 2. **Initiation** - Initiation of transcription in bacteria begins with the binding of RNA polymerase to the **promoter region** (PR) in DNA. - The **promoter** is a segment of DNA that signals which DNA strand is transcribed and the direction of transcription. - The PR of DNA **indicates the starting point of transcription**, and there may be multiple promoter sequences within a DNA molecule. **Promoter Region** - are DNA sequences that define where transcription of a gene by RNA polymerase begins. - **Promoter sequences** are typically located directly upstream or at the 5\' end of the transcription initiation site. - RNA polymerase and the necessary transcription factors bind to the promoter sequence and initiate transcription. - Many eukaryotic genes have a conserved promoter sequence called the **TATA box,** located 25 to 35 base pairs upstream of the transcription start site. - In eukaryotes, genes transcribed into RNA transcripts by the enzyme RNA polymerase II are controlled by a **core promoter.** **TATA Box** - is a DNA sequence that indicates where a genetic sequence can be read and decoded. - It is a type of promoter sequence, which specifies to other molecules where transcription begins. **DNA Replication** - Process in which the cell makes an identical copy of itself - The first step is to "unzip" the double helical structure of DNA catalyzed by the enzyme **helicase** which breaks the hydrogen bonds holding the complimentary bases of DNA - The unwinding of the 2 single strands of DNA results in a **replication fork** 3. **3' to 5' direction** - **Leading Strand** - (towards the replication fork) - Continuous - Template Strand - Antisense strand 4. **5' to 3' direction** - **Lagging strand** - (away from the replication fork) - Discontinuous - Coding strand - Sense Strand **In the leading strand:** - A **primer binds** to the end of the leading strand and acts as the starting point for DNA synthesis - **DNA polymerase** binds to the leading strand and "walks" along the strand adding new complimentary nucleotide bases to the strand of the DNA in a 5' to 3' direction; - **replication is continuous** **Lagging strand** - Numerous **primers** bind at various points along the lagging strand - these act as starting points for the addition of complimentary bases in the 5' to 3' direction producing fragments called **Okazaki fragments** - replication in the lagging strand is **discontinuous** - Once all the complimentary bases are in place, an enzyme called **exonuclease** will catalyze the removal of the primer sequences - The gaps are then filled with complimentary bases - The enzyme **ligase** joins the fragments to make 2 continuous double stranded DNA - The product of DNA replication are 2 DNA molecules consisting of one new and one old chain of nucleotides, hence semiconservative - Following replication, the new DNA winds up into a double helix **Process of Transcription** - **Not all of the DNA sequence is used to make protein.** - Following transcription, new, immature strands of messenger RNA, called **pre-mRNA,** may contain both introns and exons. - **Introns** are non-coding sections of an RNA transcript, or the DNA encoding it, that are spliced out before the RNA molecule is translated into a protein. - **Introns** are referred to as **intervening sequences.** - The sections of DNA (or RNA) that **code for proteins** are called **exons**. **RNA Splicing** - The pre-mRNA molecule thus goes through a modification process in the nucleus called **splicing** during which the non-coding introns are cut out and only the coding exons remain. - Splicing produces a **mature messenger RNA** molecule that is then translated into a protein. **Process of RNA Splicing** 1\. A group of 5 snRNPs are needed to attach to the intron of pre-mRNA and remove it, leaving only the exons. 2\. The snRNPs attach to the intron and make it fold, bringing the ends of the intron closer together to form a loop. The ends of the exons also come together to connect. 3\. The intron comes off, and the splice sites join to create a mature mRNA. The snRNPs detach from the intron and can be used again for more splicing. **Spliceosome** - is a large RNAprotein complex that catalyzes the removal of introns from nuclear premRNA. - The pre-mRNA which has been transcribed will also undergo processing to convert it into the mature RNA Processing includes: 1. **5' Capping** - Capping involves the addition of a methylated guanine cap to the 5′ end of mRNA. Its presence is vital for the recognition of the molecule by ribosomes, and to protect the immature molecule from degradation by RNAses. 2. **3' Polyandenylation** - Polyadenylation involves the addition of a poly(A) tail to the 3′ end of mRNA. The poly(A) tail consists of multiple molecules of adenosine monophosphate. This helps to stabilize RNA, which is necessary as RNA is much more unstable than DNA. **Mature mRNA** - By the end of transcription, mature mRNA has been made. - This acts as the messaging system to allow translation and protein synthesis to occur. - Within the mature mRNA, is the **open reading frame (ORF**). This region will be translated into protein. It is translated in blocks of three nucleotides, called **codons**. - At the 5' and 3' ends, there are also **untranslated regions (UTRs).** These are not translated during protein synthesis. **Translation** \- The way information in messenger RNA (mRNA) is turned into proteins. \- This process happens in the cytoplasm on a structure called the ribosome. \- Amino acids used to make proteins are first linked to transfer RNA (tRNA). Each tRNA matches specific groups of 3 nucleotides in the mRNA, called codons. \- The nucleotides in the mRNA are read in groups of 3 based on the genetic code. \- tRNA molecules act as helpers -- one end reads the triplet code in the mRNA, and the other end attaches to a specific amino acid. \- Ribosomal RNA (rRNA) helps attach each new amino acid to the chain being formed. \- The first tRNA, with the amino acid methionine, attaches to the P site of the ribosome. The A site is ready to match with the next codon using the next tRNA. The ribosome has three sites for tRNA to attach: 1\. A (amino acyl) site \- This is where the tRNA matches its anticodon with the mRNA codon to add the right amino acid to the growing chain. 2\. P (peptidyl) site \- This is where the amino acid moves from its tRNA to the growing chain. 3\. E (exit) site \- This is where the empty tRNA waits before going back into the cytoplasm to pick up another amino acid and start again. **Steps in Translation** \- To start translation, a small part of the ribosome attaches to the mRNA at the start codon (AUG) recognized by the first tRNA. \- A large part of the ribosome attaches to finish forming the ribosome and start the next stage. \- During this stage, tRNAs with specific amino acids attach one by one to the matching codon in the mRNA by pairing with the tRNA anti-codons. \- Each amino acid is added to the end of the growing chain by repeating the steps of tRNA binding, making a bond, and moving the ribosome. \- This goes on from the 5' to 3' direction until one of the three stop codons (TAA, TAG, TGA) is reached. \- A release factor then attaches to the ribosome, ending translation and freeing the finished protein. The cell reads the DNA code in groups of three bases. Each group of three bases, known as a codon, stands for specific amino acids. **HSP70 System** \- The HSP70 chaperone system includes the main chaperone HSP70 and many helpers. It helps proteins fold properly, fix their shape, and break down damaged proteins. \- It acts like a watchful system that catches proteins that are not shaped correctly. \- HSP70 grabs and releases proteins using energy from ATP. \- The work of HSP70 in folding and breaking down proteins is controlled by helper proteins like HSP40 and HIP, and by other partners like the enzyme CHIP. \- BAG1 and BAG3 also connect to HSP70 and adjust its work, linking it to the process that destroys proteins (BAG1) and to another method of breaking down proteins called macroautophagy (BAG3). **Post-translational modification (PTM)** - of proteins refers to the chemical changes that occur after a protein has been produced. It can impact the structure, electrophilicity and interactions of proteins. 1. Phosphorylation Addition of phosphate group to a protein, typically by kinase to **regulate protein function** 2. Methylation - Addition of methyl group to **modify protein activity or stability** 3. Sulfation - Addition of sulfate group for **structural changes and protein-protein interactions** 4. Acetylation - Addition of acetyl group affecting **protein function or stability** 5. Ubiquitination - Attachment of ubiquitin molecules **for degradation or regulating protein** 6. Prenylation - Addition of lipid groups for **membrane targeting** 7. SUMOylation - Attachment of small ubiquitin like modifier (SUMO) proteins affecting **localization or protein function** 8. Palmitoylation - Attachment of palmitate ( a lipid molecule) to proteins for **membrane association** 9. Glycosylation - Addition of sugar molecules to proteins, **influencing protein folding, stability and function**