Molecular and Cellular Biology Lecture 2

Questions and Answers

What is a defining feature of eukaryotic cells?

Rolling DNA structure

Single-celled structure

Presence of a nucleus (correct)

Absence of membrane-bound organelles

Which statement is true regarding prokaryotic cells?

They are typically multicellular organisms.

They have a well-defined nucleus.

They are seen in most complex life forms.

They contain rolling pieces of DNA. (correct)

What is the primary role of DNA in living organisms?

Forming structural components of the body

Transporting information throughout the cell

Providing templates for protein synthesis

Holding information on how the cell functions (correct)

Which characteristic distinguishes eukaryotic cells from all living forms?

Presence of chromosomes inside the nucleus Signup and view all the answers

How do RNA molecules function within a cell?

They transfer short pieces of information and provide templates for protein synthesis. Signup and view all the answers

What are the three parts that make up a nucleotide?

A nitrogenous base, a phosphate group, and a five-carbon-atom sugar Signup and view all the answers

Which of the following bases is found exclusively in RNA?

Uracil (U) Signup and view all the answers

What is the significance of the double hydrogen bond between A and T in DNA?

It provides stability to the DNA structure. Signup and view all the answers

What role does the helicase enzyme play during DNA replication?

It unwinds the double helix structure of DNA. Signup and view all the answers

How does DNA replication maintain its semi-conservative nature?

One strand is newly created while one strand is conserved from the parent DNA. Signup and view all the answers

Study Notes

Cells and Their Types

Cells are the fundamental units of all living systems.
Specialization leads to the formation of tissues, which consist of groups of cells for specific functions.
There are 14 major tissue types including bone, muscle, nerve, and fat.
Over 200 different cell types exist with a common genetic code.

Eukaryotic vs. Prokaryotic Cells

Eukaryotic cells can be single or multicellular, possess a nucleus, and have membrane-bound organelles.
Prokaryotic cells are single-celled organisms lacking a nucleus and membrane-bound organelles; they typically contain a single, rolled-up DNA strand.

Nucleic Acids Overview

Life relies on three critical molecules: DNA, RNA, and proteins.
DNA stores cellular information, RNA transfers information and synthesizes proteins, while proteins perform vital cellular functions and form structural components.

Nucleotides and Their Components

Nucleic acids like DNA and RNA are polymeric chains composed of nucleotides, which include:
- A nitrogenous base
- A five-carbon sugar
- A phosphate group.

DNA (Deoxyribonucleic Acid)

DNA carries genetic instructions and has a double helix structure, discovered by Watson and Crick.
It consists of two complementary antiparallel strands running 5' to 3' and 3' to 5'.
The structure comprises nitrogenous bases (A, C, G, T), deoxyribose sugar, and phosphate groups.
Adenine pairs with thymine via double hydrogen bonds, while guanine pairs with cytosine through triple hydrogen bonds.
DNA is more stable than RNA due to its deoxyribose sugar.

DNA Replication Process

Initiation: Helicase unwinds DNA, creating a replication fork; primase synthesizes an RNA primer.
Elongation: DNA polymerase adds nucleotides complementary to the template strand; lagging strand forms in fragments (Okazaki fragments).
Termination: Exonuclease removes RNA primers, DNA polymerase fills gaps, and DNA ligase seals the strands.
DNA replication is semi-conservative, retaining one original strand in each new DNA molecule.

RNA (Ribonucleic Acid)

RNA functions in protein coding and acts as a carrier.
RNA is structured as a single helix and runs from 5' to 3', including components similar to DNA.
It contains nitrogenous bases (A, C, G, U) with adenine pairing with uracil, and guanine pairing with cytosine.
RNA is less stable than DNA because of its ribose sugar.

Major RNA Types

Messenger RNA (mRNA): carries the genetic message from the nucleus to the ribosome for protein synthesis.
Transfer RNA (tRNA): transfers specific amino acids to the ribosome to build proteins.
Ribosomal RNA (rRNA): combines with proteins to form ribosomes.
Non-coding RNA: does not translate into proteins; examples include tRNA and rRNA.
Catalytic RNA: catalyzes chemical reactions.
Double-Stranded RNA: has complementary strands like DNA and can influence gene expression.

Description

Dive into the fascinating world of cells as we explore Eukaryotes and Prokaryotes, and uncover the structures of DNA and RNA. This lecture addresses crucial concepts in molecular biology including nucleic acids and their role in life. Perfect for students in the field of biology or related studies.