Year 12 Biology Notes PDF

There are two basic types of cells : 1. Prokaryotes 2. Eukaryotes - **Prokaryotes (example bacteria) are approximately 1 micrometer in size** - **Genetic material is a single circular piece of coiled DNA** - **No true nucleus (no membrane around DNA)** - **DNA is located in a reg...

There are two basic types of cells : 1. Prokaryotes 2. Eukaryotes - **Prokaryotes (example bacteria) are approximately 1 micrometer in size** - **Genetic material is a single circular piece of coiled DNA** - **No true nucleus (no membrane around DNA)** - **DNA is located in a region called the nucleoid** - **Contain ribosomes** - **No membrane bound organelles** **Eukaryotes** - Genetic material DNA is linear (chromosomes) - Have a true membrane bound nucleus - Region between the nucleus and the cell membrane is called the cytoplasm - Suspended in the cytoplasm are membrane bound organelles that have specialised structures and functions - Large size between 10-100 micrometres **Comparison between eukaryotic and prokaryotic cells q**  Cytoplasmic streaming- movement of cytoplasm which is driven by forces from the cytoskeleton Histones- Histones are proteins that bind to DNA in chromosomes, helping to condense DNA and regulate gene activity **Macromolecules** Large molecules found inside a living organism are called macro molecues They usually have many smaller unites joined together 4 major types of organic compounds in cells and organisms Each macromolecule group (polymer) are made from different types of monomers (subunits): - Proteins -- Amino acids - Lipids -- Fatty acids and glycerol - Carbohydrates/Polysaccharides -- Sugars/Monosaccharides - Nucleic Acids -- Nucleotides There are two types of nuecleic acid DNA- deoxyribonucleic acid RNA- ribonucleic acid **DNA** Deoxyriobucleic acid (DNA) is a macromolecule found in all living cells and controls everything that happens in a cell It is the fundamental chemical of life The structure of DNA was discovered by James Watson and Francis Crick. Watson-Crick model of DNA structure. Discovery of DNA - DNA was first isolated in 1859 by a Swiss chemist called Friedrich **Miescher**, who discovered it was acidic and contained the element phosphorus. - Because it was consistently found in the nucleus of cells, it was called a *nucleic acid*. - In the early 1950s, American biologist James **Watson** and British physicist Francis **Crick** released their famous model of the DNA double helix - DNA was first isolated in 1859 by a Swiss chemist called Friedrich **Miescher**, who discovered it was acidic and contained the element phosphorus. - Because it was consistently found in the nucleus of cells, it was called a *nucleic acid*. - In the early 1950s, American biologist James **Watson** and British physicist Francis **Crick** released their famous model of the DNA double helix **Chromosomes and DNA** DNA is found in structures called chromosomes Chromosomes are used to store and transmit genetic information DNA is stuffed into chromosomes by proteins called **histones** which act as spools which dna winds around The tips of each chromosome are short lengths of DNA called telomeres. Telomeres protect the structure from breakdown and stop the chromosomes from binding to each other. **DNA in prokaryotes** **It is located in the liquid parts of the cytoplasm (cytosol)** **It has a single circular double stranded DNA molecule that is different from a cells chromosomal DNA.** **Plasmids naturally exist in bacterial cels** **Genes carried in plasmids provide bacteria with genetic advantages such as antibiotic resistance** **DNA in eukaryotes** - **Located in the nucleus of the cell** - **Linear strands of DNA** - **Made of chromatin which cannot be distinguished under a microscope** - **When the cell divides, the chromatin condenses to form thicker, more visible structures called chromosomes** **Extra information about DNA** - **Two types of membrane bound organelles also contain DNA: mitochondria (mitochondrial DNA or mtDNA) and chloroplasts.** - **Specific to each organelle and separate from chromosomal DNA** - **MtDNA and DNA found in chloroplasts is double stranded but circular and not bound to proteins.** - **There are theories for the existence of DNA in these organelles -- mitochondria and chloroplasts were once "free-living" unicellular organisms capable of their own existence** - **This supports the idea that simple organisms (ancient versions mitochondria and chloroplasts) came together within a membrane to make more complex cells.** **RNA compared to DNA** **RNA is single stranded while DNA is double** **RNA has the bases A, U, G and C** **RNA has ribose sugar, DNA has deoxyribose sugar** **Uracil is energetically less expensive to produce than thymine** **RNA and DNA are both involved in protein synthesis** **RNA is a temporary store of genetic information before this is passe on for protein synthesis.** **Chromosomes in humans** **In human cells there are 23 pairs of chromosomes (46 individual chromosomes total)** **One pair called the sex chromosomes determines the sex of a human** **The ther 22 pairs called autosomes and determine a variety of other characteristics** **A complete set of chromosomes lined up in ordered pairs is called a karyotype.** **Chromosomes and genes difference** **Gene- a segment of DNA on a chromosome that contains the complete sequence of bases needed t direct the manufacture of a protein or RNA** **Each gene has a specific (fixed location) on a particular chromosome** **recap** **DNA** - **chemical unit of genetic information** **Genes** - **functional units of genetic information** - **Specific DNA sequences** - **determine protein synthesis, physical characteristics and inheritance** **Chromosomes** - **structural units of genetic information** - **short thick linear structures** - **form just before cell division as chromatin condenses** - **many genes on each chromosome** **Chromatin** - **long thread like structure made up of DNA wrapped up with proteins (histones)** - **present when the cell is not dividing** **Chromatids** - **Duplicate copies of chromosomes, only present during cell division (mitosis and meiosis)** - **Sugar molecule** - **Phosphate group** - **Nitrogen base** **Phosphate of one nucleotide is attached to sugar of the next nucleotide** **Reaching across from the sugars , the nitrogenous bases pair up** **Complementary base pairing**  - Adenine Always Binds To Thymine - Guanine Always Binds To Cytosine **DNA replication** **Before a cell divides it must copy its entire DNA in the nucleaus so that each of the new cells have identical copies** **The process of DNA replication must be completed before cell division can occur** **The structure of DNA lends itself easily to DNA replication. Each side of the double helix runs in opposite (anti-parallel) directions to allow the structure to unzip down the middle and each side serves as a pattern or template for the other side (called semi-conservative replication -- one old, one new strand).** A blue circle with yellow lines and red arrow Description automatically generated  **DNA replication process** 1. **The enzyme helicase unzips and splits the DNA double helix into two strands by breaking the hydrogen bonds between the bases.** 2. **The two strands act as templates for new strands of DNA** 3. **Free nucleotides in the nucleus bind to their complimentary base pair on both the template and complimentary strands of the DNA** 4. **Then DNA Polymerases (enzyme) joins free nucleotides together to form a growing DNA strands** 5. **The two pairs of DNA strands then re-twist into two separate (but identical) DNA molecules.** 6. **An enzyme called DNA ligase seals up the fragments into one long continuous strand** 7. **As each DNA molecule contains one old strand and one new strand, the process is called semi-conservative replication** DNA Polymerase Function The replication of DNA occurs under the influence of more than a dozen enzymes including helicases, DNA polymerases and DNA ligases **Enzyme** **Function** ---------------- --------------------------------------------------------- Helicases Unwind/unzip the DNA double helix Primases Initiate replication Polymerases Catalyse the synthesis of new complementary DNA strands Ligase Joins DNA fragments together Topoisomerases Involved in the re-coiling of the DNA - DNA replication is not able to occur an unlimited number of times because every time SNA in chromosomes is replicated, the telomeres at the ends of the chromosome shorten - Every time a cell carries out DNA replication, the chromosomes are shortened by about 25-200 bases per replication. - After a certain number of replications (on average 50-70 times), the telomeres are too short for further replication - This 'critical length' triggers the cell to die by a process called apoptosis, also known as programmed cell death. **Key concepts** - DNA is the genetic material that stores and transmits information and is found in cells - Chromosomes are the structural units of information made up of DNA. In eukaryotic cells, DNA is bound to protein molecules called histones - Chromosomes are either linear or circular and are not visible in non-dividing cells - Most chromosomes in eukaryotic cells are linear and are found in the nucleus of the cell - Chromosomes in prokaryotic cells are circular, not bound to proteins and found in cytosol - DNA is made up of two complementary strands that form a double helix structure - Each DNA strand is made up of repeating units called nucleotides - One nucleotide is made up of three molecules -- a deoxyribose sugar, an organic base (A, T, G, C),and a phosphate group - DNA molecules are copied in a process called semi-conservative DNA replication **1.2 Language of life** **Genes and chromosomes** A gene is a special sequence of DNA nucleotides that code for a specific protein or RNA molecule Each gene has a special location on a certain chromosome Genes are inheritable factors responsible for the physical characteristics or phenotype of an organism It does so by specifying the structure of a protein/RNA molecule \\ **Human Genome** The total number of genes in an organism is its genome A persons genotype with other factors determine their phenotypic traits (appearance) Changes in genes drive evolution and natural selection - When genes mutate, variants (alleles) are formed and this results in differences in phenotypic traits **Genes and proteins** **Genes code for the synthesis of specific proteins** **Many proteins are constructed from2 or more polypeptide chains, with each polypeptide being coded for by a different gene.** **A polypeptide is a single chain of amino acids** **Amino acids are the monomers of protein molecules** **The unique DNA base sequence of a genes actually codes for the sequence of amino acids in a polypeptide chain** **Amino acids** **There are 4 DNA bases but 20 amino acids** **Triplets of DNA bases code for 1 amino acids** - **(e.g. AAA codes for phenylalanine)** - **4^3^ = 64 possible combinations of 3 bases** **More than 1 triplet can code for an amino acid** **The information coded in DNA is transcribed on to a mRNA molecule.** - **On mRNA a triplet of bases (e.g.UUU) is called a codon.** **codon chart\ ** **example question** A screenshot of a test Description automatically generated **DNA to protein** DNA is like a manual for the building of different proteins a cell needs to operate and survive - DNA is a long molecule and lies tangled inside the nucleus - Nucleus has a membrane which selectively allows molecules in - Synthesis of proteins occurs outside the nucleus at organelles called ribosomes but DNA cannot leave the nucleus A copy, mrna of the segment of DNA (gene) needed to construct the desired polypeptide is made within the nucleus and brought out to the cytoplasm (transcription) The information carried within this copy of the gene is then translated to direct the building of the desired polypeptide from free amino acids in the cytoplasm This process is called protein synthesis **Protein synthesis** The production of protein is called protein synthesis -protein sysnthesis is the process by which cells build proteins Protiesn are long strings of amino acids Protein synthesis occurs in 2 stages 1. Transcription (in the nucleus a temporary copy of a DNA segment is made= mRNA) 2. Translation (in the cytoplasm, the copy is decoded to construct a polypeptide)  **RNA and protein synthesis** There are 3 types of RNA molecules involved in protein synthesis - rRNA (ribosomal RNA)- works with proteins to form ribosomes the site of protein synthesis - tRNA (transfer RNA)- carriers of amino acids during protein synthesis (anticodon) - mRNA (messenger RNA) -- transcribed from DNA to carry the gene message out to ribosomes for translation into an amino acid sequence **RNA vs genes** RNA is different from DNA for 3 reasons: Oxygen in the sugar (ribose vs [deoxy]ribose) DNA is double stranded, RNA is single stranded There is a base change in RNA, Uracil (U) not Thymine (T) **Transcription** Happens first in protein synthesis and its purpoe is to transcribe DNA into a message to create proteins Occurs in the nucleus The genetic information is carried on only one of the two strands of the DNA. This is known as the ***coding strand***. The other strand is known as the ***template strand*** Since mRNA is a complementary copy of the **template** DNA segment. What will it be the same as? Transcription 1. The enzyme RNA polymerase separates the two strans of DNA to expose the bases 2. Free nucleotides inside the nucleus bind to the bases on the exposed template strand of DNA (A to T / U to A/ C to G/ G to C) 3. RNA polymerase enzyme joins free nucleotides to for a mRNA strand 4. Once transcription is complete, mRNA strand is **modified** to remove **non-coding regions**. 5. The mRNA then moves out of the nucleus and into the **cytoplasm** through pores in the **nuclear membrane.** 6. Unzipped segment of the DNA strand **re-joins** to reform the double stranded helix. Hydrogen bonds reform.  **Introns and exons** DNA contains coding and non-coding segments Exons= coding DNA (expressed) -transcribed into mRNA then translated into protein Introns= non-coding (inbetween exons) -tnracribed into an RNA molecule but doesn't code for a protein \- cut out after transcription to produce mature mRNA  **Translation** Translation is the process of translating the sequence of a mRNA molecule to a sequence of amino acids. Polypeptide chain is built using a sequence of codons in mRNA molecule Transfer RNA molecules are required to transfer AA from the cytosol to the mRNA strand **Ribosomes**: made of rRNA and is the site where amino acids are joined to form polypeptides **tRNA**: cloverleaf shaped molecule with 3 exposed bases (anticodon) and an amino acid attachment site. Carries specific amino acids to the ribosome A diagram of a plant tissue Description automatically generated mRNA feeds through a ribosome 2 codons at a time. **Tranlsation** **Transfer rna, brings free floating amino acids found in the cytoplasm to the ribosome** **Each tRNA positions itself along the mRNA strand in accordance to the mRNA codons** **A peptide link is created between each amino acid** **The tRNA is able to move away and find another amino acid once it has dropped the old amino acid off.** **Once a stop codon is attached to the ribosome, the protein has been made** **The mRNA can be used to make many proteins or can be dissolved If not needed.** **Trnaslation can be broken down into 3 stages** 1. **Initiation: the start codon AUG starts the process** 2. **Chain elongation: the building of the AA sequence from the coodns** 3. **Termination: the completion of the mRNA sequence with a stop codon (UAG, UAA, UGA)**