BIOLOGY- U4T1 DNA structure + replication

DNA

DNA (deoxyribonucleic acid) is the hereditary material in all living organisms, responsible for the storage and transmission of genetic information.

RNA

Its principal role is to act as a messenger carrying instructions from DNA for controlling the synthesis of proteins, although in some viruses RNA rather than DNA carries the genetic information.

What is the structure of DNA

Double-stranded, twisted into a double helix. Bases pair A–T and C–G via hydrogen bonds

What is the structure of RNA

Single-stranded and typically shorter than DNA. Does not form a double helix.

Sugar in DNA

Deoxyribose – a five-carbon sugar lacking one oxygen atom compared to ribose.

Sugar in RNA

Ribose – a five-carbon sugar with one more oxygen atom than deoxyribose.

Bases in DNA

A, T, C, and G – the nitrogenous bases are adenine, thymine, cytosine, and guanine. These bases pair specifically: A with T and C with G, contributing to the double-helix structure.

Bases in RNA

Adenine (A), Uracil (U) (instead of Thymine), Cytosine (C), Guanine (G)– the nitrogenous bases include adenine, uracil, cytosine, and guanine.

mRNA, tRNA, rRNA

MESSENGER- A single-stranded RNA molecule that carries the genetic code from DNA to the ribosome, where it is used as a template for protein synthesis.

TRANSFER- A cloverleaf-shaped RNA that brings specific amino acids to the ribosome. It has an anticodon that pairs with codons on the mRNA during translation.

RIBOSONAL- A structural component of ribosomes. It helps form the ribosome and catalyses the formation of peptide bonds between amino acids during protein synthesis.

Location of DNA

In eukaryotes, mostly in the nucleus (bound to histones); also in mitochondria and chloroplasts.

Location of RNA

Synthesized in the nucleus and functions mainly in the cytoplasm.

Histone

A protein that DNA wraps around to form chromatin in eukaryotic cells, helping to compact and organize DNA.

Circular DNA

A form of DNA that is looped and unbound by histones, found in prokaryotes, mitochondria, and chloroplasts.

Nucleotide

The basic building block of DNA, made up of a phosphate group, a deoxyribose sugar, and a nitrogenous base.

Hydrogen bonds

Weak bonds between complementary nitrogenous bases (A–T have 2 bonds, C–G have 3 bonds) that hold the two DNA strands together

Double Helix

The twisted ladder shape of DNA formed by two antiparallel strands held together by base-specific hydrogen bonds.

DNA Replication

The process by which DNA makes an exact copy of itself during cell division.

Helicase

An enzyme that unwinds the DNA double helix and separates the two strands by breaking hydrogen bonds between bases.

DNA Polymerase

An enzyme that builds new DNA strands by adding complementary nucleotides in the 5′ to 3′ direction, using the original strand as a template.

Antiparallel Strands

The two strands of DNA run in opposite directions—one 5′ to 3′, the other 3′ to 5′.

Leading Strand

The DNA strand that is synthesized continuously in the 5′ to 3′ direction during replication.

Lagging Strand

The DNA strand that is synthesized in short fragments (Okazaki fragments) in the opposite direction of the replication fork.

Semi-Conservative Replication

Each new DNA molecule consists of one original (parent) strand and one newly synthesized strand.