Section D- Synthesis and release of proteins.
Content
A. The role of DNA, RNA and cellular organelles:
LO 1. Know the functional variety of proteins.
LO 2. State the elements which proteins contain and explain why proteins have a unique shape and structure.
LO 3. Explain the bonding that are involved in protein structure.
Notes
Proteins are composed of carbon, hydrogen, oxygen and nitrogen, they can often contain sulphur. Proteins are made from chains of amino acids, joined by peptide bonds. They are also called polypeptide chains.
There are 20 different types of amino acids. The structure and properties of each protein depends on the length of the amino acid chain, and the order of the amino acids that form the chain.
Weak chemical bonds known as hydrogen bonds form between certain amino acids in a polypeptide chain causing the chain to become coiled into a spiral.
Several polypeptide chains can also become linked together by a variety of cross-connections including: sulphur bridges and additional hydrogen bonding.
Extra

LO 4. Explain the functions of proteins in plants and animals as enzymes, hormones, regulating proteins and structural proteins, and give examples of each group.
Proteins can be classified as either fibrous or globular.
Fibrous proteins (e.g. collagen) are insoluble structural proteins from which many body tissues such as bone, ligament, muscle and hair are built. They are formed by several spiral-shaped polypeptide chains becoming linked together in parallel by cross bridges.
Globular proteins are not truly soluble.
They form suspensions in water and can have a variety of functions, for example as enzymes, membrane proteins, some hormones and antibodies.
They are formed by several polypeptide chains folded together into a roughly spherical shape.
Some proteins you should know:
Enzymes, Membrane proteins, Hormones and Antibodies.
Conjugated proteins consist of globular proteins with a non-protein part,
Examples: Glycoprotein and
Haemoglobin.

B. DNA: structure, in particular the double helix, nucleotides and bases; pairing of named bases; genes as regions of chromosomal DNA; the processes of DNA replication and its importance.
LO 5. State that chromosomes are made of
DNA, and that genes are small sections of
DNA which code for a particular protein.
LO 6. Describe the structure of DNA.
LO 7. Describe the structure of a nucleotide and explain why there are 4 nucleotides.
LO 8. Explain base pairing in DNA and give the base pairs.
LO 9. Explain DNA replication and state what this process needs.
LO 10. Explain DNA replication and state what this process needs.
Chromosomes are thread like structures made of Deoxyribonucleic acid (DNA).
DNA is a double helix made of units called nucleotides.
A nucleotide is made of a deoxyribose sugar, a phosphate and one of the four bases: adenine (A), thymine (T), guanine
(G) and cytosine (C).
A strong chemical bond joins the phosphate group of one nucleotide to the deoxyribose sugar of the nucleotide above it to form a chain, or backbone.
There are two strands of DNA chains opposite each other. They are joined with weak hydrogen bonds between the bases that pair up in the middle.
The bases pair up: A-T and C-G.
These two strands coil around each other to form a helix.
For DNA to replicate there must be a supply of free nucleotides, the correct enzymes and energy from ATP.
DNA polymerase links the nucleotides in the chain.

LO 11. Explain why DNA replication is essential.
LO 12. Explain the triplet code.
C. RNA: single strand structure; replacement of thymine with uracil and deoxyribose with ribose; mRNA transcription; functions of mRNA and tRNA in synthesis of proteins; triplet code; codons and anti-codons.
LO 13, Name two forms of RNA.
LO 14. Describe the structure of messenger
RNA
Replication produces two identical DNA molecules consisting of a new strand and an old strand. This is called semi- conservative replication.
DNA replication ensures that an exact copy of the species genetic information is passed from cell to cell.
The sequence of bases on the DNA is arranged as genes. These are pockets of information. Each gene codes for a protein.
The bases are read in groups of three called triplets.
Ribonucleic acid (RNA) is the second type of nucleic acid. An RNA nucleotide consists of ribose sugar, a phosphate and one of four bases. The bases are the same as the bases in DNA except
Thymine. This is replaced by Uracil (U).
RNA is single stranded.
Messenger RNA (mRNA) is formed in the nucleus using the DNA as a template. This is called transcription.

LO 15. Give three differences between mRNA and DNA.
LO 16. Describe the stages of transcription.
LO 17, Describe a codon.
Transcription: a short length of DNA uncoils and unzips, this requires enzymes and energy from ATP. Free RNA nucleotides bond to the exposed bases on one DNA strand by complementary base pairing. Adjacent RNA nucleotides join to form a sugar-phosphate backbone. mRNA molecule peels off of the DNA which zips back up. mRNA molecule moves out of the nucleus to attach to a ribosome for protein synthesis.
The mRNA strand is also read in triplets called a codon.
A second type of RNA is found in the cell’s cytoplasm called transfer RNA
(tRNA). Each molecule of tRNA is only three bases at one end, called an anticodon. and an amino acid at the other end.
The tRNA pairs with the mRNA and brings together the amino acids in the correct sequence so that they can be joined into the polypeptide chain. Once the amino acid is joined the tRNA leaves the mRNA and collects a free amino acid to repeat the process.

D. Cellular organelles: ribosomes and rough endoplasmic reticulum. Distribution within the cell and function as site of transplantation in protein synthesis; role of endoplasmic reticulum in transporting proteins; role of
Golgi apparatus in processing molecules for secretion.
LO 18. State the functions of ribosomes in protein synthesis.
LO 19, Describe the process of translation in the ribosome involving mRNA, tRNA and amino acids.
LO 20. Describe the processes of packaging and secretion of enzymes,
LO 21. Explain the function of the Golgi apparatus.
Ribosomes are the site of protein synthesis where the sequence of mRNA triplet codes are translated into proteins.
Some ribosomes are attached to the endoplasmic reticulum, some are free in the cytoplasm.
Endoplasmic reticulum is a continuous network of membranes throughout the cell, it functions as a transport system for proteins.
Most proteins are used in the cell which produces them, some proteins such as hormones and digestive enzymes are secreted for use elsewhere.
Proteins are processed or ‘packaged’ for secretion from the Golgi apparatus.
Golgi apparatus attaches various carbohydrates to the protein molecules, making them glycoproteins.
Vesicles pinch off the ends of the Golgi body and carry the protein to the plasma membrane of secretion.