DNA Structure: Double Helix

DNA Structure

Double Helix

• Description: A double-stranded helix where two complementary strands of DNA are twisted together.
• Key features:
  • Right-handed spiral staircase structure
  • Sugar-phosphate backbone forms the outer rails
  • Nitrogenous bases project inward and pair with each other
  • Distance between each turn: 34 angstroms (Å)
  • One full turn: 10 base pairs
• Importance:
  • Allows for compact storage of genetic information
  • Provides a mechanism for replication and transcription

Nucleotides

• Definition: The building blocks of DNA, composed of three components:
  1. Sugar molecule (deoxyribose): Forms the backbone of DNA
  2. Phosphate group: Links sugar molecules together, forming the backbone
  3. Nitrogenous base: Projects inward from the backbone and pairs with other bases
• Types of nitrogenous bases:
  • Purines: Adenine (A) and Guanine (G)
  • Pyrimidines: Cytosine (C) and Thymine (T)
• Base pairing rules:
  • Adenine (A) pairs with Thymine (T)
  • Guanine (G) pairs with Cytosine (C)
• Importance:
  • Nitrogenous bases encode genetic information
  • Base pairing rules ensure complementary strands are formed during DNA replication

DNA Structure

Double Helix

• Double-stranded helix with two complementary DNA strands twisted together
• Right-handed spiral staircase structure with sugar-phosphate backbone forming outer rails
• Nitrogenous bases project inward and pair with each other
• Distance between each turn is 34 angstroms (Å) with 10 base pairs per full turn
• Importance: allows for compact storage of genetic information and provides mechanism for replication and transcription

Nucleotides

• Building blocks of DNA, composed of sugar molecule (deoxyribose), phosphate group, and nitrogenous base
• Sugar molecule forms backbone of DNA
• Phosphate group links sugar molecules together, forming backbone
• Nitrogenous base projects inward from backbone and pairs with other bases
• Types of nitrogenous bases: purines (Adenine (A), Guanine (G)) and pyrimidines (Cytosine (C), Thymine (T))
• Base pairing rules: Adenine (A) pairs with Thymine (T), Guanine (G) pairs with Cytosine (C)
• Importance: nitrogenous bases encode genetic information, base pairing rules ensure complementary strands are formed during DNA replication

Kāna and its Sisters

Verb Conjugation

• Kāna and its sisters are a group of Arabic verbs that convey a sense of being or existence
• These verbs are irregular and do not follow the usual patterns of Arabic verb conjugation
• Conjugation patterns for Kāna:
  • was/were
  • he was: كَانَ (Kāna)
  • you (m.) were: كُنتَ (Kunta)
  • you (f.) were: كُنتِ (Kunti)
  • we were: كُنَّا (Kunnā)
  • you (pl.) were: كُنتُم (Kuntum)
  • they were: كُنَّ (Kunna)

Sentence Structure

• Kāna and its sisters are used to form sentences that describe a state or condition
• Basic sentence structure: Kāna + subject + predicate
• Example sentence: كَانَ زيدٌ مريضًا (Kāna Zaydun marīḍan) - Zayd was sick
• The verb is usually in the third person singular (he/she/it) form, followed by the subject and then the predicate

Irregular Verb Forms

• Kāna and its sisters have irregular forms in the past tense
• Other irregular verbs that belong to this group:
  • أصبح (Aṣbaḥa) - to become
  • أضحى (Aḍḥā) - to become
  • ظَلَّ (Ẓalla) - to remain
  • أمسى (Amsā) - to become
• Each of these verbs has its own unique conjugation pattern

Tense Usage

• Kāna and its sisters are used to describe completed actions in the past
• They can also be used to express a state or condition that existed in the past
• The verb is often used in combination with other verbs to form more complex sentences
• Examples of sentence usage:
  • كَانَ زيدٌ يَدرُسُ (Kāna Zaydun yadrusu) - Zayd was studying
  • كَانَتِ فاطِمَةُ تَكْتُبُ (Kānat Fāṭimatu taktubu) - Fāṭima was writing