Science 9th grade honors DNA & Protein Synthesis

DNA

Deoxyribose Nucleic Acid

What is DNA held together by?

Two hydrogen bounds

What is DNA made of?

A phosphate, pentose (5C) sugar and a nitrogenous base.

What are the four nucleotides

A, Adenine T, Thymine G, Guanine C, Cytosine.

Purines

A nucleotides that have a double ring in their nitrogenous base (A and G).

Pyrimidines

They have a single ring (C and T)

Complementary base pairs

A binds to T & G binds to C

Chargaff's rule

%A = %T & %G = %C

Anti-parallel strand

The head of one strand (5' end) is opposite to the tail of the other strand (3' end).

Suger-phosphate back bone

Forms the strands

Where are the hydrogen bounds in DNA?

Forms between nitrogenous base and holds the strands together.

Chromatin

DNA is condensed by wrapping around histone proteins, which form nucleoside which combine to form chromatin.

Chromosome

Chromatin being further condensed.

When does DNA replication take place?

Occurs during the (S)ynthesis phase of the Cell Cycle.

DNA helicase

Unravels the DNA molecule.

DNA polymerase

Adds DNA nucleotides to developing DNA strand.

Topoisomerase

Stabilizes the unraveled DNA molecule.

DNA primase

Adds RNA primer.

DNA ligase

Stitches together Okazaki fragments.

What do all chromosomes have?

Origin of replication (ori).

Two replication forks

DNA replicates in both directions.

Steps of DNA replicaton

1. Replication fork

2. DNA Helicase (breaks hydrogen bonds), primase DNA polymerases (adds nucleotides), DNA ligase glues together Okazaki fragments.

Leading strand

Pointing in the

"correct" direction for replication..

Lagging strand

Is in the "wrong"

direction.

Okazaki fragments.

Synthesis of the lagging strand occurs in small, discontinuous stretches.

Templet strand

A model, to produce the new strands.

What is the RNA nucleotide that replaces Thymine?

Uracil replaces Thymine.

What type of RNA are there?

rRNA, mRNA, and tRNA

What is mRNA?

Messenger RNA, carries genetic

code to ribosome during protein synthesis.

What is rRNA?

rRNA: ribosomal RNA, used to build

ribosomes.

What is tRNA?

tRNA: transfer RNA, delivers amino

acids to ribosome during protein

synthesis.

Protein Synthesis

Process of building proteins that occurs at the ribosomes (both free

ribosomes and those on the ER).

What are the two major steps in protein synthesis?

Transcription & Translation.

When does protein synthesis occur during the cell cycle?

Occurs during G1 and G2 phases of the

cell cycle.

Transcription

Copy the message of DNA into RNA (specifically mRNA).

Initiation in Transcription

DNA unwinds at the initiation site due to the promoter.

Elongation in Transcription

RNA polymerase creates antiparallel transcript using RNA nucleotides (no proofreading).

Termination in Transcription

Specified by a specific DNA base sequence.

Translation

The goal of translation is to convert the

message of the mRNA 🡪 protein.

Genetic code

Specifies which amino acids will be used to build a protein.

Codon

A sequence of three bases on

mRNA. Each codon specifies a particular

amino acid.

Start codon

AUG—initiation signal for translation.

Stop codons

UAA, UAG, & UGA—stops translation and polypeptide is released

What does EPA sites stand for?

Amino acid, Polypeptide, & Exit.

A site

Binds with anticodon of charged tRNA.

P site

Where tRNA adds its amino acid

to the growing chain.

E site

Where tRNA sits before being

released.

Initiation

Begins with Start Codon (AUG).

Elongation

Codons from mRNA are matched to anticodons on tRNA via complementary base pairing. Amino acids are combined in a specific order to form a polypeptide chain.

Termination

Ends with Stop Codon (UGA, UAG or UAA). Release factor detaches polypeptide chain from ribosome.

TATA Box

The TATA box is a specific DNA sequence

within the promoter region, usually consisting of

a repeating TATA sequence.

Where is the tata box located?

It's located about 25-35 base pairs upstream of

the transcription start site in many eukaryotic

genes.

Splicing

Introns (non-coding regions) are removed,

and exons (coding regions) are joined together by a

complex called the spliceosome to create a

continuous coding sequence.

5' Capping

A modified guanine nucleotide is added

to the 5' end of the mRNA, protecting it from

degradation and helping it bind to the ribosome

during translation.

3' Polyadenylation

A string of adenine nucleotides (the poly-A tail) is added to the 3' end, stabilizing the mRNA and aiding in its export to the cytoplasm.

Base substitutions

Correct nucleotide is replaced with another nucleotide.

Insertions

An extra nucleotide(s) is added to the sequence.

Deletions

Nucleotide(s) is/are removed from the sequence.

Point mutations

Only affect a single nucleotide in a DNA/RNA sequence.

Frameshift

mutations alter the entire reading frame of the DNA/RNA sequence.

Silent mutations

Does not change the amino acid coded for by the codon.

Nonsense mutations

Convert the codon to a stop codon.

Missense mutation

Change the amino acid coded for by the codon.