Biology Exam - (RNA, RNA, and Proteins)

Moleculer Biology covering (DNA, RNA, and Proteins)

DNA - what is the structure and function

DNA is a molecule that stores the genetic instructions an organism needs for growth, repair, reproduction, and making proteins.

• DNA stands for deoxyribonucleic acid.

• It is found mainly in the nucleus.

• Its shape is a double helix, which looks like a twisted ladder.

• DNA controls inherited traits by giving instructions for protein production.

Nucleotides

Nucleotides are the small repeating units that join together to make up a DNA strand.

• Each nucleotide has three parts: a sugar, a phosphate group, and a nitrogen base.

• DNA is made from many nucleotides linked together.

• The order of the nucleotides forms the genetic code.

deoxyribose

Deoxyribose is the five-carbon sugar found in DNA nucleotides.

• It is part of the backbone of DNA.

• It joins with phosphate groups to form the sides of the DNA ladder.

• RNA has ribose instead, not deoxyribose.

purines

Purines are the larger nitrogen bases in DNA, and they include adenine and guanine.

• Adenine (A) and guanine (G) are purines.

• Purines always pair with pyrimidines.

• This helps keep the DNA molecule the same width.

pyrimidines

Pyrimidines are the smaller nitrogen bases in DNA, and they include thymine and cytosine.

• Thymine (T) and cytosine (C) are pyrimidines.

• Pyrimidines pair with purines in DNA.

• This pairing keeps the DNA structure balanced.

complementary bases

Complementary bases are the specific base pairs in DNA that always match in the same way.

• Adenine pairs with thymine.

• Cytosine pairs with guanine.

• These pairing rules are important for DNA replication and protein synthesis.

 anti-parallel

Anti-parallel means that the two strands of DNA run in opposite directions.

• One strand runs one way and the other runs the opposite way.

• This arrangement helps enzymes copy DNA properly.

• It is an important part of DNA’s structure.

adenine

Adenine is a nitrogen base in DNA that always pairs with thymine.

• Its symbol is A.

• It is a purine.

• In RNA, adenine pairs with uracil instead of thymine.

thymine

Thymine is a nitrogen base in DNA that always pairs with adenine.

• Its symbol is T.

• It is a pyrimidine.

• Thymine is found in DNA, but not in RNA.

cytosine

Cytosine is a nitrogen base in DNA that always pairs with guanine.

• Its symbol is C.

• It is a pyrimidine.

• It follows the complementary base-pairing rule.

guanine

Guanine is a nitrogen base in DNA that always pairs with cytosine.

• Its symbol is G.

• It is a purine.

• It helps complete one of the DNA base pairs.

DNA Replication – steps and enzymes involved

DNA replication is the process where DNA makes an exact copy of itself before the cell divides.

• This happens before mitosis or meiosis.

• It makes sure each new cell gets the same genetic information.

• The process uses enzymes to unzip and rebuild DNA.

Semi-conservative

Semi-conservative replication means that each new DNA molecule contains one original strand and one newly made strand.

• Half of the original DNA is kept in each new copy.

• This helps preserve genetic information accurately.

• It is the accepted model of DNA replication.

parent strand

A parent strand is one of the original DNA strands that serves as a template during replication.

• The old strand guides the building of the new strand.

• New nucleotides are added based on complementary base pairing.

• Each parent strand becomes part of a new DNA molecule.

lagging strand

The lagging strand is the new DNA strand that is built in short pieces during replication.

• It is made in sections because it runs in the opposite direction.

• These short pieces are called Okazaki fragments.

• The fragments must later be joined together.

leading strand

The leading strand is the new DNA strand that is built continuously during replication.

• It is made in one smooth direction.

• DNA polymerase can follow the replication fork easily on this strand.

• It does not need to be built in fragments.

helicase

Helicase is the enzyme that unwinds and unzips the DNA double helix at the start of replication.

• It breaks the hydrogen bonds between base pairs.

• This separates the two DNA strands.

• It creates the replication fork.

primers

Primers are short RNA sequences that give DNA polymerase a place to start building a new DNA strand.

• DNA polymerase cannot start on its own.

• Primers are laid down before new DNA nucleotides are added.

• They are later replaced with DNA.

primase

Primase is the enzyme that makes the RNA primers needed for DNA replication.

• It adds the short starter sequence.

• This allows DNA polymerase to begin copying the DNA.

• It works on both the leading and lagging strands.

DNA polymerase

DNA polymerase is the enzyme that adds new DNA nucleotides to the growing strand during replication.

• It matches bases using complementary base-pairing rules.

• It builds the new strand in the correct order.

• It also helps proofread for mistakes in some cases.

Ligase

Ligase is the enzyme that joins DNA fragments together by sealing the sugar-phosphate backbone.

• It is especially important on the lagging strand.

• It connects the Okazaki fragments into one continuous strand.

• It acts like a glue for DNA.

SSSBs (Single-strand binding proteins)

Single-strand binding proteins, or SSSBs, are proteins that keep the separated DNA strands from joining back together during replication.

• They stabilize the open DNA strands.

• They help keep the replication process organized.

• Without them, the strands could reattach too soon.

Okazaki fragments

Okazaki fragments are the short pieces of DNA that are formed on the lagging strand during replication.

• They are made because the lagging strand is copied in sections.

• Each fragment starts with a primer.

• Ligase later joins them together.

 RNA – structure, types, function

RNA is a nucleic acid that helps carry and use genetic information to make proteins.

• RNA stands for ribonucleic acid.

• It is usually single-stranded.

• It contains ribose sugar.

• It uses uracil instead of thymine.

mRNA

Messenger RNA, or mRNA, is the type of RNA that carries genetic instructions from DNA to the ribosome.

• It is made during transcription.

• It contains codons that tell the order of amino acids.

• It acts like a message copied from DNA.

tRNA

Transfer RNA, or tRNA, is the type of RNA that brings amino acids to the ribosome during translation.

• Each tRNA has an anticodon.

• The anticodon matches with a codon on mRNA.

• This helps place the correct amino acid in the growing protein.

rRNA

Ribosomal RNA, or rRNA, is the type of RNA that makes up part of the ribosome and helps with protein synthesis.

• It helps hold mRNA and tRNA in place.

• It is part of the structure of the ribosome.

• It also helps form peptide bonds between amino acids.

ribose sugar

Ribose sugar is the five-carbon sugar found in RNA.

• It is different from deoxyribose in DNA.

• Ribose is part of the backbone of RNA.

• It helps make RNA chemically different from DNA.

single helix

A single helix means that RNA usually has only one strand instead of the double-stranded structure of DNA.

• RNA is not shaped like a twisted ladder.

• Because it is single-stranded, it can move more easily in the cell.

• This makes it useful in protein synthesis.

uracil

Uracil is the nitrogen base in RNA that replaces thymine and pairs with adenine.

• Its symbol is U.

• In RNA, A pairs with U.

• Uracil is only found in RNA, not DNA.

codon

A codon is a group of three bases on mRNA that codes for one amino acid or a stop signal.

• Codons are read during translation.

• Each codon has a specific meaning on the codon chart.

• For example, some codons signal start or stop.

anticodon

An anticodon is a group of three bases on tRNA that pairs with a codon on mRNA.

• The anticodon makes sure the right amino acid is brought in.

• It is complementary to the mRNA codon.

• This helps build the correct protein sequence.

Protein Synthesis – steps of transcription and translation, using codon chart

Protein synthesis is the process cells use to make proteins based on the instructions in DNA.

• It has two main stages: transcription and translation.

• It turns genetic information into a working protein.

• Proteins are important for traits, enzymes, and cell functions.

Transcription

Transcription is the process where a section of DNA is copied into mRNA in the nucleus.

• RNA polymerase attaches to DNA.

• It reads one DNA strand as a template.

• It builds a complementary mRNA strand.

introns

Introns are sections of RNA that are removed before the mRNA leaves the nucleus.

• Introns do not code for amino acids.

• They are cut out during RNA processing.

• They are not used in the final protein message.

exons

Exons are the sections of RNA that remain after introns are removed and are used to code for proteins.

• Exons stay in the final mRNA molecule.

• They contain the instructions for amino acid order.

• They are joined together before translation.

poly-A tail

The poly-A tail is a string of adenine bases added to the end of mRNA after transcription.

• It helps protect the mRNA from breaking down.

• It helps the mRNA leave the nucleus.

• It also helps the ribosome recognize the mRNA.

translation

Translation is the process where the ribosome reads mRNA and builds a protein from amino acids.

• It happens at the ribosome in the cytoplasm.

• tRNA brings amino acids in the correct order.

• The ribosome links them together to form a protein.

ribosome

A ribosome is the cell structure where translation happens and proteins are made.

• It reads the codons on mRNA.

• It works with tRNA and rRNA.

• It joins amino acids together in the right sequence.

amino acids

Amino acids are the small molecules that join together to make proteins.

• They are the building blocks of proteins.

• The order of amino acids determines the protein’s shape and function.

• Each codon on mRNA codes for a specific amino acid.

 polypeptide bonds

Peptide bonds are the chemical bonds that join amino acids together in a growing protein chain.

• These bonds form during translation.

• The ribosome helps create them.

• A chain of amino acids joined by peptide bonds is called a polypeptide.

RNA polymerase

RNA polymerase is the enzyme that builds mRNA during transcription by using DNA as a template.

• It attaches to a gene on the DNA.

• It reads the DNA sequence.

• It puts together a complementary RNA strand.

Using a codon chart

A codon chart is used to match each mRNA codon to its correct amino acid during translation.

• You read the mRNA codon, not the DNA strand.

• Every 3 bases gives one amino acid.

• Some codons are start codons and some are stop codons.

Gene mutations – define and identify different types

A gene mutation is a change in the DNA base sequence of a gene.

• Mutations can happen during replication or because of outside factors.

• Some mutations have no effect, while others can change proteins.

• Mutations can be small or large.

Point mutation

A point mutation is a mutation that affects only one nucleotide or one base pair in the DNA sequence.

• It usually involves a substitution.

• It changes only one position in the code.

• It may or may not affect the protein.

 neutral mutation

A neutral mutation is a mutation that does not significantly affect the function of the protein.

• The protein may still work normally.

• Sometimes the amino acid change does not matter much.

• Neutral mutations do not usually cause noticeable effects.

silent mutation

A silent mutation is a mutation where the DNA base changes but the amino acid stays the same.

• This happens because some amino acids are coded for by more than one codon.

• The protein does not change.

• It is usually harmless.

missense mutation

A missense mutation is a mutation where one base changes and causes a different amino acid to be placed in the protein.

• This can change the protein’s shape or function.

• Some missense mutations have small effects, while others are serious.

• It depends on which amino acid is changed.

nonsense mutation

A nonsense mutation is a mutation where a base change creates a stop codon too early.

• This causes translation to stop before the protein is finished.

• The protein is usually shorter than normal.

• It often makes the protein nonfunctional.

 substitution

A substitution is a mutation where one base is replaced by another base.

• It is a type of point mutation.

• It can cause a silent, missense, or nonsense mutation.

• Only one base is switched.

Frameshift mutation

A frameshift mutation is a mutation that changes the reading frame of the genetic code by adding or removing a base.

• It affects every codon after the mutation.

• It usually has a major effect on the protein.

• Insertion and deletion are the main types of frameshift mutations.

deletion

A deletion is a mutation where one or more nucleotides are removed from the DNA sequence.

• If the number removed is not a multiple of three, it causes a frameshift.

• This can completely change the amino acid sequence after that point.

• It often causes serious protein changes.

insertion

An insertion is a mutation where one or more nucleotides are added into the DNA sequence.

• If the number added is not a multiple of three, it causes a frameshift.

• This changes the codon grouping.

• It can greatly affect the final protein.