Proteins and DNA PDF

# Proteins and DNA ## Proteins - **Proteins** are the building blocks of our bodies. - They perform a wide range of functions, such as: - **Structural support**: *e.g.* collagen in skin and bones, keratin in hair and nails. - **Transport**: *e.g.* hemoglobin in red blood cells carries oxy...

# Proteins and DNA ## Proteins - **Proteins** are the building blocks of our bodies. - They perform a wide range of functions, such as: - **Structural support**: *e.g.* collagen in skin and bones, keratin in hair and nails. - **Transport**: *e.g.* hemoglobin in red blood cells carries oxygen. - **Catalysis**: *e.g.* enzymes speed up chemical reactions. - **Defense**: *e.g.* antibodies fight infections. - Proteins are made up of **amino acids**. - **Amino acids** have different chemical properties, and they fold into specific shapes based on their interactions. - This shape determines the function of the protein. ### Levels of Protein Structure 1. **Primary Structure:** The sequence of amino acids. This sequence is unique for each protein and is determined by the organism’s genetic code. 2. **Secondary Structure:** The local folding patterns of the polypeptide chain, such as **alpha-helix** and **beta-sheets**. 3. **Tertiary Structure:** The overall 3D shape of a single polypeptide chain, formed by interactions between different amino acids. 4. **Quaternary Structure:** The arrangement of multiple polypeptide chains in a protein complex. ## DNA - **DNA** stands for deoxyribonucleic acid. - It is the genetic material of all living organisms. - It contains the instructions for building and maintaining an organism. - DNA is stored in the **nucleus** of cells. ### Structure of DNA - DNA is a **double helix**. - Each strand of the helix is made up of a chain of **nucleotides**. - Each nucleotide consists of: - **Deoxyribose sugar** - **Phosphate group** - **Nitrogenous base**: - **Adenine (A)** - **Thymine (T)** - **Guanine (G)** - **Cytosine (C)** - The two strands of DNA are held together by **hydrogen bonds** between the nitrogenous bases. - **A** always pairs with **T**. - **G** always pairs with **C**. ### DNA Function - The sequence of nitrogenous bases in DNA carries the genetic information. - This information is transcribed into **RNA** and then translated into proteins. ## Gene Expression - A **gene** is a segment of DNA that codes for a specific protein. - **Gene expression** is the process of converting genetic information into a functional product. ### Transcription - The process of copying the genetic information from DNA into RNA. - Happens in the nucleus of the cell. - Starts with **initiation**: RNA polymerase binds to the promoter region of the gene. - **Elongation**: RNA polymerase moves along the DNA, using the template strand to build a complementary RNA strand. - **Termination**: When RNA polymerase reaches a termination signal, it detaches from the DNA. ### Translation - The process of synthesizing a protein from the information carried in mRNA. - Happens in the cytoplasm of the cell, on **ribosomes**. - **Initiation**: mRNA binds to ribosomes. The first tRNA carrying the amino acid methionine binds to the start codon AUG. - **Elongation**: Ribosomes move along the mRNA, reading the codons and adding the corresponding amino acids to the polypeptide chain. - **Termination**: The ribosome reaches a stop codon, and the polypeptide chain is released. ## Control of Gene Expression - Gene expression is tightly regulated to ensure that the correct proteins are produced at the right time and place. - Some proteins are always produced, while others are only produced under specific conditions. - **Enhancers:** Bind to activator proteins and stimulate gene expression. - **Silencers:** Bind to repressor proteins and inhibit gene expression. ## Chromosomes - **Chromosomes** are structures made of DNA and proteins. - They are found in the nucleus of eukaryotic cells. - **Chromatin** is the complex of DNA and proteins that makes up chromosomes. - **Euchromatin:** Loosely packed chromatin, where genes are actively transcribed. - **Heterochromatin:** Tightly packed chromatin, where genes are generally inactive. - **Sister chromatids** are two identical copies of a chromosome, joined together by the **centromere**. - During cell division, chromosomes are replicated and separated into daughter cells. ## Summary This document provides a basic overview of proteins and DNA, including: - The structure and function of proteins, - The structure and function of DNA, - The processes of gene expression including transcription and translation, - The regulation of gene expression. - The structure of chromosomes. This information is crucial for understanding the fundamental principles of molecular biology and how genetic information is used to build and maintain living organisms.